---

InspectAPedia ^® Home

AIR CONDITIONING & HEAT PUMP SYSTEMS

A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE EFFICIENCY RATINGS

BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books

CAPACITORS for HARD STARTING MOTORS
CAPILLARY TUBES
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS

DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY

ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS

FAN LIMIT SWITCH
FAN NOISES

GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS

HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEAT PUMPS
HEATING SMALL LOADS

INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS

LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST

MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK

OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING

REPAIR GUIDE, AIR CONDITIONERS / HEAT PUMPS
REPAIR & DIAGNOSTIC FAQs for A/C

SWAMP COOLERS

THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES

WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS

More Information

How to Diagnose a Burned-out Air Conditioning Compressor       How to diagnose a burned-out air conditioning compressor When is a compressor at or near end of its life? Criteria for deciding that an air conditioner, heat pump, or refrigeration compressor needs to be replaced Hard starting air conditioner compressor Increased air conditioning electrical bills Air conditioner compressor defect diagnosis & repair guide Air conditioning condenser unit fan diagnosis/repair When to replace a failing or failed A/C or heat pump compressor Common causes of A/C or heat pump compressor motor failure Questions & Answers about air conditioning and heat pump compressors: diagnosis, failure, repair, replacement References

Click to Show or Hide Related Topics

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This air conditioning repair article discusses the how to diagnose and replace a burned out air conditioner compressor, including evaluation of air conditioner compressor noises, hard starting, lost cooling capacity, and detection of a burned out compressor or A/C compressors at or near end of their life. Here we catalog and describe the causes of air conditioner or heat pump compressor failures and we suggest compressor motor diagnostic steps. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution

Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.

How to Diagnose a Burned-Out Air Conditioning Compressor

Air conditioner failure warning signs: Before an air conditioning compressor fails solid you may notice that the unit is hard-starting, particularly when starting against a head pressure (someone switched the system off while the compressor was running, then tried turning it right back on). See CAPACITORS for HARD STARTING MOTORS and see MOTOR OVERLOAD RESET SWITCH.

Another sign of a failing air conditioning compressor is noisy motor operation, such as buzzing or clanking sounds coming from the outside unit housing the compressor motor. See NOISES, COMPRESSOR CONDENSER.

Another sign that might indicate a failing air conditioner compressor motor is an increase in the building's electrical bills even though the air conditioning system "on" time has not changed. See TIGHT or SEIZED AC COMPRESSORS where we provide additional details about examining and measuring A/C and heat pump compressors to continue compressor condition diagnosis.

When a sealed compressor motor has "burned out" this means that the internal wiring of the motor has become irreparably damaged: the compressor motor windings may be burned and shorted together or shorted to the steel shell of the motor, or the windings may have burned and simply become "open" or disconnected. If the motor has burned out in either of these ways it needs to be replaced.

When an air conditioner / heat pump compressor can no longer develop proper pressures, even if its electric motor has not burned out, the unit will still need to be replaced. Below we give refrigerant pressure details that help make this decision.

Basic Diagnostic Clues Indicating a Failed A/C or Heat Pump Compressor Motor

Watch out for shock hazards or equipment damage: see USING DMMs VOMs SAFELY.

The compressor won't start, perhaps just hums, and the motor star/run capacitor(s) are ok or you've tried replacing that part

As soon as the compressor tries to start the circuit breaker trips or fuse blows. The compressor motor has burned out, is internally shorted or gounded. A service technician will use a VOM and typically will find low resistance (low Ohms) between one or more compressor terminals and ground.

A VOM connected to the compressor circuit indicates that no current is being drawn, but the condenser fan is running properly.
Watch out: before assuming that the compressor motor is bad, when the unit won't start at all, check for a loose or disconnected electrical connection or a bad contactor relay. An overheated motor may also leave the compressor motor "off" due to a tripped internal overload switch or a switch that has simply failed. If this is the problem, the motor should start normally once the unit has cooled down. (Some readers describe spraying water on the condenser unit to speed cooling - (don't wet electrical switches & components.)

Basic Electrical Tests on Air Conditioner or Heat Pump Compressor Motors

Watch out for shock hazards or equipment damage: see USING DMMs VOMs SAFELY.

When an air conditioning compressor has "burned out" by shorting of internal components - it will fail to start at all. This failure is detected by disconnecting all power and wiring from the unit and measuring resistance (ohms) between the motor start/common and run/common terminals.

Zero resistance: If there is zero resistance the winding is open or broken.

Infinite resistance: If you measure the resistance across a compressor winding and your meter's needle is stuck over at infinity, or "OL"/"OVER" on a digital meter, that would indicate the compressor winding is open (burned through). The same effect can be observed from simply connecting the meter to absolutely nothing. Typically if just one widing is "open" you'll see infinite resistance at one check point and in contrast (for the non-open windings) you will read zero resistance ("continuity") between the Common terminal and the Start or between the Common terminal and Run terminal.

Low resistance: If the resistance measured across the air conditioning compressor winding is too close to 0 ohms, it's shorted. The compressor should blow the fuse or trip the circuit breaker when power is turned back on. But watch out: we get field reports of equipment burn ups and even fires when the air conditioning circuit breaker for the compressor happens to be an old FPE Stab-Lok or Zinsco unit.

If there is resistance but not infinite resistance between the motor terminal and the motor casing, the motor has become shorted to ground internally and the unit needs to be replaced. If there is no resistance between the start and run terminals to common, but there is resistance between the start and run terminals, this means that the internal motor overload protection circuit is open. In this last case, allow the motor to cool and re-test it before replacing it. See REPLACING A COMPRESSOR.

For details about measuring RLA / FLA, and definitions of RLA, FLA, and LRA, see see TIGHT or SEIZED AC COMPRESSORS

Other (Non-Electrial) Refrigeration Compressor Failure Modes

Watch out: for a mechanically frozen compressor: a compressor may pass all of these electrical tests and still require replacement. The tests above only test electrical connections and windings. An air conditioner or heat pump or refrigeration compressor that has jammed up mechanically internally will still refuse to start (perhaps will hum) when all of the electrical tests, contactor relay, start capacitor, etc. are tested as perfecliy fine.

A compressor with broken internal parts may also not be frozen, that is its internal electrical motor may start and run, but the compressor fails to produce any refrigerant pressure at its outlet side. In this case internal parts or valves in the unit have broken without jamming the motor itself. In this case, all of the electrical components and tests will look "OK".

A compressor with broken internal motor mounts may make a rattling or clanking sound and needs replacement. It will continue to run but could become shrapnel at any time.

A compressor with bad internal valves will continue to run but is inefficient and should be replaced. The symptom is very quick equalization of high and low side pressure as soon as the motor stops.

When to replace a sealed-unit air conditioning or heat pump compressor?

Burned up electric motor in the HVAC compressor

Some compressor motor failures are so apparent that there's no question: an electric motor burnout that draws high amps or is internally shorted, for example.

Abnormal HVAC compressor pressures

But what about a compressor motor that may be just "worn" ? An HVAC compressor should be able to pull at least 15" of vacuum against 100 psi head pressure or else it is inefficient. Of course to make this test you must be able to isolate the compressor from the rest of the cooling or heat pump system, so this test is not rapidly made in the field.

Bad HVAC compressor refrigerant valves

Bad air conditioner reed valves will be unable to pull pressure down on the low side of the system. A leaky discharge reed valve (on the compressor output side) pulls hot gases back into the compressor cylinder and recompresses them, causing abnormally high head pressures at the compressor motor. And as a result the compressor won't be able to move vapor.

In sum, HVAC compressors do fail and need replacement, but only when you have tested and ruled out the other 80% of the causes of common air conditioning, heat pump, or refrigeration problems (usually electrical in nature) do you go ahead and replace the compressor unit.

General advice: Electrical Tests to Check HVAC Blower Fan Motor or Outdoor Compressor Fan Motor Winding on Heating or Cooling Equipment or on Other Electrical Motors

Air Conditioner Compressor/Condenser Fan Not Working?

Details of compressor/condenser unit fan inspection, diagnosis, and repair are at FAN, COMPRESSOR/CONDENSER UNIT. Basic advice follows:

A failed compressor/condenser fan can cause the air conditioning system to shut down due to an overheating compressor or excessive pressures developed inside the compressor. If your compressor/condenser unit does not include a safety override switch to perform this shutdown and if the condenser unit fan is not working, your compressor motor may be permanently damaged. At NOISES, COMPRESSOR CONDENSER we include some condenser fan noise problems are traced to the cooling fan motor, bearings, fan blades, obstructions, etc.

Watch out: if your compressor/condenser unit motor is running but the fan itself is not blowing air, the system will not work and may be seriously damaged. The outdoor cooling fan or condenser unit fan is needed not only to cool high pressure, high temperature refrigerant in gas form so that it can condense back to liquid form.

That cooling step also cools down the compressor itself and keeps the compressor internal pressure from becoming too high. Most modern compressor / condenser units include an overpressure sensor that will shut the equipment down if compressor pressures become too high. Some older models and some modern economy air conditioner compressors may lack this function.

See USING DMMs VOMs SAFELY. Example: testing a blower fan motor winding: referring to the electrical diagram for your equipment, unplug electrical connectors at the fan motor. Measure the resistance between each lead wire with a multimeter or VOM. The multimeter should be set in the X1 range. For accuracy, don't measure when the fan motor is hot, allow it to cool off.

When the resistance between each lead wire are those listed in the specifications for your equipment the fan motor should be normal. Zero resistance or infinite resistance are indicators of a problem. More examples of checking wiring: see BURNED-OUT COMPRESSOR. See HARD STARTING COMPRESSOR MOTORS also TIGHT or SEIZED AC COMPRESSORS for more details about old or failed compressor motors. Also see Test a Motor Starting Capacitor

Common Causes of Burned Out Air Conditioner Compressors

• Contamination of refrigerant, piping, or devices in the refrigeration system: contaminants, including air, moisture carried in by air, and dirt can enter the refrigeration system as contaminants due to a leak on the suction side or improper service procedures such as mis-handling of service port valves or opening the system for repairs without adequately drawing a vacuum and without proper use of filter/dryer canisters. Air in the system can also lead to refrigerant flooding discussed above.
• Cooling problems - compressor motor overheats: a compressor motor that keeps on running when the compressor/condenser fan has failed or when air flow through the condensing coil has become blocked by debris or damage can cause abnormally high compressor head pressures and operating temperatures. If the condenser fan is running but airflow is impaired the system may continue to "run" but at reduced cooling capacity and shortened compressor life. We found a stack of nine A/C compressors improperly installed without adequate cooling air flow at a wealthy client's home in Pawling, NY. Compressor motors were being replaced every year or two because the owner installed a stockade fence to "hide the ugly equipment". A compressor may also run too hot due to too-high temperatures at the suction line and low-side of the compressor system. Under-charged refrigerant levels or lack of insulation on the suction line piping can cause these problems as might a TEV that is not quite flooding the system but is releasing refrigerant too fast through the cooling coil. [2]
• Refrigerant Pressure problems - excessive high side pressure may be caused by a restriction or blockage such as in the condensing coil, refrigerant metering device, or even at the cooling coil. Excessive high side pressure causes hot compressor operation, lost cooling capacity, and ultimately damage.
• Refrigerant flooding - sending liquid refrigerant into the compressor motor is a quick way to destroy its moving parts or valves. We discuss refrigerant flooding and six common causes of liquid refrigerant slugging the compressor at THERMOSTATIC EXPANSION VALVES, and aside from TEV (TXV in some literature) problems, a mistake like overcharging the system can lead to liquid refrigerant can end up in the compressor bottom where only refrigerant gas is expected - causing the same failure problems. Christopherson, [2]
• Refrigeration oil lubricant - lost due to system leaks (most likely you'll know there has been a history of refrigerant leakage too); also refrigeration oil can travel in the refrigerant lines where it reaches a capillary tube or TEV , clogging it and causing abnormal system pressures that can damage the compressor. On commercial refrigeration systems that us a separate oil pump to deliver lubricant to the compressor motor, an oil pump failure also leads to compressor motor failure.
• Electrical problems that can damage A/C or heat pump motors are cited by Christopherson, including improper voltage (hooking up to an incorrect voltage level supply (110V to 220V or 230V applied to a 208V motor), poor power quality delivered to the system such as at homes subject to significant fluctuations in actual voltage levels in the incoming mains, loss of voltage on one phase of a three-phase electrical hookup (more common on commercial than residential refrigeration equipment), and finally, unbalanced current across the individual phases of a three-phase electrical hookup. [2]
• Worn out compressor internal parts - a compressor motor may fail due to mechanical wear, though in our OPINION and having seen some refrigeration compressor motors that ran for decades with no trouble, we think mechanical wear is likely to be traced to a refrigerant, lubrication, contamination, or perhaps mounting problem. See our contamination comments above.

The text above describing causes of refrigeration compressor damage is indebted to HVACR experts Norm Christopherson [2] and Joe Marchese [6], as well as Warren Hilliard [1].

Frequently Asked Questions (FAQs) about how to diagnose and fix air conditioning and heat pump compressors

Question: My air conditioner compressor blew, the new system is icing up, what's going on?

I am a 100% service-connected disabled veteran who just spent over $3700. to replace a 4 ton trane xr12 air conditioner condenser and coil. My old condenser compressor blew up and the HVAC guy said it wasn't worth replacing since the unit was a 9 yr old r-22 system.

He talked me into a new trane xr13, 4 ton, r-410 condenser and a 5 ton evaporative coil for an extra $400. saying I'd get 10% more cooling capacity than the 4 ton coil. this was 5 weeks ago. three techs have been here since trying to figure out why the evaporative coil keeps icing up. the best cooling we get with the thermostat set at 72 degrees is only 15 degrees cooler than it is outside.this is with the front panel off the furnace.

With the panel in place, in 2 or 3 days the coil turns into a block of ice. even with the panel off, as the day wears on and the outside temperature drops, the inside temperature increases. right now, the thermostat is at 72, it's10:15 p.m. it's 73 degrees outside and 76 degrees inside.

The HVAC guys tried to blame my ductwork as unable to handle the airflow, then inadequate air returns, then too small a hole (10x12) above the coil going to the plenum. all solutions of course would require a 2nd mortgage. My response was . BULL. It's something they did wrong because before the compressor blew, if the outside temperature was 100 degrees, inside it was 78 degrees.(with the thermostat set at 72.

Not once in 9 years did it ice up or did I ever have to remove the front panel of the furnace to increase the airflow., It has to be one or both of the things they installed, like maybe a defective evaporator coil. Do you have any suggestions? Thanks - B.H.

Reply:

Cooling coil icing can be due to an improper refrigerant charge, inadequate air flow across the cooling coil, or a problem with a refrigerant metering device (or something else we haven't thought-of). Your HVAC guys might be right that your old duct system is not moving enough air across the coil, allowing it to ice up, but if that's the problem I'd ask them why they didn't think of that before selling you that extra big evaporative coil in the air handler. In a good-working air conditioner or heat pump system the components need to be in balance: compressor/condenser, air handler/evaporator, and ductwork.

If we hold off on the blame game for a bit, let's see if you can increase the airflow across the coil. Often I find on older cooling systems that the return air opening was too small or the connections from return register to the air handler small or cramped or twisty. A very crude "test" that I do NOT RECOMMEND for more than a few minutes of test operation is to see if the coil ices up if someone leaves the air handler blower compartment door off - to maximize the return air opening. Take a look under DUCT SYSTEM & DUCT DEFECTS for the article: RETURN AIR REGISTERS & DUCTS, and also take a look under COOLING COIL or EVAPORATOR COIL at the article: FROST BUILD-UP on AIR CONDITIONER COILS for more help.

Finally, at RETROFIT SIZING for A/C or HEAT PUMPS we touch on the importance of balancing the system components during a retrofit or upgrade of an air conditioner or heat pump system.

Let us know what you find - we'll both learn something.

Question: what does it mean if the outside compressor seems to work ok if I cool it with a garden hose?

If my fan blade had slipped (now fixed) and the compressor was overworked, is it normal for a technician to cool it off with a garden hose? Thank you - Audra 6/12/11

Reply:

Audra, we've seen techs or homeowners cool down a compressor with a garden hose, but of course if the compressor is overheating because it's worn or damaged that fix is not at all lasting. In the case you describe, as long as the compressor/condenser fan was fixed, I am guessing that the tech just wanted to get things moving quickly again and didn't want to wait for the system to cool down normally.

Question: air conditioner air flow is reduced and air is not cold - cooling fan not running?

Blower fan running but reduced air flow (Dirty filter?) Air is not cold. System was on for a couple of hours when I noticed condenser fan. It was not running. Turned system off, waited a while, turned system on. Condenser fan hummed but was not turning. Used a BBQ fork (ok, not smart but I’ve never been accused of being too bright) to hit fan and it started. Still no cold air, ran for an hour, compressor fan motor and compressor VERY hot (Burned my fingers twice to confirm, that "not so bright thing again.”) Suggestions? - William 6/21/11

Reply:

William: when the outside compressor motor runs but the cooling fan does not, I suspect a bad start/run capacitor on the fan motor (if yours uses one) or a bad fan motor; sometimes it's a bad control board circuit. If (with power turned off for safety) the fan spins freely if pushed, the motor is probably not frozen; in that case also see if there is a motor overload reset switch that can be pressed.

Question: my A/C compressor trips the circuit breaker, what might be wrong?

my compressor shorts out my breaker, I tested the compressor with an ohm meter and reads voltage. what can it be? - Chico 7/1/11

Reply:

Chico: if your air conditioner compressor shorts out and trips the circuit breaker I'm afraid the compressor motor may be seized.

Question: squealing compressor fan, fan motor replaced, now unit is blowing hot air

Late last week, the fan on my outside unit began making a squealing sound and next morning the unit was blowing very warm air inside. I walked outside and found the
Fan had stopped but the motor seemed to still be running. I then shut the unit off and called a repair service to fix or replace the fan motor. Motor was replaced and seemed
to be working properly. Now, after 5 days of use, the fan has again stopped and the unit
is once again blowing hot air. Anyone have any suggestions? - Ronnie 7/3/11

Reply:

Ronnie: if your fan motor was replaced and the new motor has also burned up I wonder if there is a fan bearing problem or an obstruction that is causing a mechanical resistance that is overloading the fan motor?

Question: A/C unit has put an inch of water on the basement floor - what might be wrong?

Our unit seemed to not be working so I just checked in the basement sound the furnace. There is about an inch of water on the floor. I shut the unit off, will Be calling the repairman soon, but am curious what you think the problem may be. - Linda 7/9/11

Reply:

Linda: you are describing the indoor air handler unit for your air conditioning (see the article link at Related Topics titled BLOWER FAN OPERATION & TESTING]

Water on the floor near your HVAC blower unit (or fan/coil unit or "indoor air handler" - all synonyms) could be from a condensate pump/drain that has stopped working or gotten clogged. Water in a condensate overflow pan will on some systems turn off the system by activating a float switch in the pan.

But another completely different condition - icing of the cooling coil - could also lead to water on the floor around the air handler when the system cycles off and the ice melts.

If your unit continued to run but was no longer cooling, I suspect this latter cause. Let us know what you find - it will help other readers.

Question: indoor fan runs, outdoor compressor won't turn on, thermostat not calling for cooling

Our fan is working on the inside, but the compressor unit will not turn on at all, so the air blowing is not cool. I've called multiple service techs, so far none can come out today (it is in the 90s!!), one MIGHT be able to come out tomorrow and I am waiting on a call back from another. Of course our house is on the market and we are supposed to have an open house tomorrow. Right now I have the whole system off at the thermostat, but keep hearing the inside system begin to start for about 5-10 seconds and then stop. Any tips to check? We've thrown the breaker to the furnace and the compressor. Our furnace is a dinosaur (but a strong one!!), the compressor unit is maybe 8 years old. - Laura 7/9/11

Reply:

Laura, I'm a little surprised that you are hearing the inside air handler running if your thermostat is not calling for cooling - could be a control problem. When a compressor won't start I first make sure there is power to the unit, which you seem to have done. Try the steps outlined in the article linked to at left of this page and titled LOST COOLING CAPACITY

Question: indoor fan runs but outdoor compressor is not spinning

My central air unit turns on, but the fan to the compressor is not spinning. Help!! - Robyn 7/26/11

Reply:

Robyn take a look at the compressor diagnostic steps suggested above: if the unit has power and your thermostat is calling for cooling but it doesn't turn on, the problem could range from a bad relay (minor expense) to a bad compressor (costly). You need a service call. But first be sure everything is turned on.

Question: noise from A/C compressor - fan had fallen off and therew was a burning smell

I investigated a noise coming from my compressor & found that the fan had fallen off and was lying at the bottom of the unit. There was a slight burning smell, but the motor still appeared to be running. I turned off the unit...Do you think the fan just needs to be reattached or does the entire motor need to be replaced? - Janet C 7/11/11

Reply:

Janet:
Good going on a commonsense investigation and diagnosis of a serious problem. Provided that the fan blades didn't damage any system components when the fan came off of the shaft, it MAY be possible to replace the fan and tighten the allen screw that holds it in place. But I'd want an expert inspection of the system before turning it back on. I'm worried that a spinning fan blade flopped around and cut a wire or damaged something.

Question: outside compressor runs but no air is coming out of air conditioning supply registers

my outside unit is running but there is no air being put out inside the house - Monica 7/20/11

Reply:

Monica,

If the compressor/condenser is running but the indoor air handler blower fan won't run you want to start diagnosing with the article linked to at Related Topics titled

BLOWER FAN OPERATION & TESTING

Check for power on at the air handler
Check for a loose fan belt or pulley
Check for a blower fan motor that is off on thermal reset

Question: air conditioner was not blowing cold air, turned it off, now it is running again, then chugg chugg sounds

Its near 100 degrees again today. Last night the A/C to the bedrooms wasn't blowing cold air so I turned it off and everyone was uncomfortable sleeping. This morning I went outside to the compressor unit (I'd turned the system on inside) to find the fan blowing normally and the compresser trying to start but not getting there. It would "chugg-chugg" for a few seconds then stop. It retried after a little bit with the same "chugg-chugg then stop." Its a York System that came with the house. Any ideas? - Will Pollock 7/22/11

Reply:

Will: you are describing a hard starting A/C compressor. A hard start kit (capacitor) might get it going again; keep in mind though that a hard starting compressor may also be near end of life.

Question: old Lennox compressor died, glowing red pipe - is there a contamination worry in the A/C system?

I have a very old Lennox compressor unit that died 2 days ago. WHen trying to determine what was wrong I turned on the unit from inside the house and when I went outside to inspect it the smell of burnt oil was in the air. Then, when I looked at the condenser, the pipe looked like it was glowing red. So, it's now time to change the unit. My question is would the pipe to my furnace and the A unit be contaminated with oil and other chemicals from the compressor? Do I have to change the complete system, or can I simply replace the compressor unit? Thanks. - Pat 7/23/11

Reply:

Pat, in short, yes.

Your description of burnt oil smell and very hot A/C compressor parts is sure evidence of a motor burnup. And you're right to worry about contaminants in the refrigeration system after a compressor motor crashes. Even the smallest amount of debris can clog the refrigerant metering device - thermal expansion valve or capillary tube.

A proper repair that involves replacing a compressor includes drawing a vacuum on the system for long enough to get as much contaminated material out as possible, and also the installation of a special compressor burnout drier filter on the system to catch remaining debris that would otherwise be circulating around in the refrigerant piping and coils.

This drier is discussed in more detail at the article REFRIGERANT DRIERS & FILTERS (links at Related Topics )

Question: trailer air conditioner not kicking in

Our air conditioner in our trailer is malfunctioning. The fan still blows wonderfully but the unit won't kick in. It tries and tries it just won't kick in. Any suggestioins - Cindy 7/27/11

Reply:

Cindy check out the diagnostic article titled DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP (link at Related Topics ) and focus on compressor/condenser no-start problems. Could be a bad relay, start/run capacitor, or motor.

Question: AC unit not cooling, very hot high pressure refrigerant line

our AC unit is not cooling, the high pressre line is VERY hot and the low pressure line is not much colder than room temp. last year we put in a new evap coil.. any ideas - Rusty 7/31/11

Reply:

Rusty, you need an expert on site to diagnose the problem. There are several problems that can give excessive pressure/temperature on the compressor outlet side of the system (the high side). Sounds like a blockage, maybe clogged dryer or bad refrigerant metering device, sometimes a clogged condensing coil.

Question: Outside AC turns on but no cool air is delivered inside. What's the cause?

our AC outside turns on but it does not blow any air inside what can be the cause of this? - Veronica 8/2/11

Reply:

Veronica if the outside compressor/condenser is working but the inside air handler/fan unit is not, take a look at the diagnostic article BLOWER FAN OPERATION & TESTING (links at Related Topics )

It could be as simple as a fan drive belt that has broken in an air handler, or a dirty air filter.

Question: can't get up to working refrigerant pressure level

The discharge line from my condenser is giving only 100 PSI, even after adding R-22 to the low side. Is my compressor defective? - Carlos 8/11/11

Reply:

Carlos, could be a bad compressor but it could also be a bad thermostatic expansion valve that is not closing.

Question: new AC unit, has trouble starting up

my air conditioner is new. its been hardly four month since i purchased it. most of the times it tries to start 2 to 3 time and then get started and some times unable to start. i dont have stablizer in my house for ac. when it runs it runs smooth and when it trips same case occur like starting can you please comment the possible casuse - Waquar Zaidi

Reply:

Wagar I'm surprised to read that a new A/C system compressor is not starting, but I suppose it could be a bad start capacitor or another bad control such as the Thermostatic Expansion valve. There are perhaps a few mistakes that could happen during installation that could destroy even a new A/C compressor such as dirt in the system or an improper refrigerant charge or a bad TEV that slugged the comprssor with liquid.

I'm unclear about the second and third sentences of your question.

Reader followup:

2nd and 3rd sentence i would like to elaborate: when compressor starts its working fine i mean it cools the room i use to run it on 26 degree centigrade and when thermostat trips and after 10 to 12 mints when compressor again tries to start same problem comes. and some time with out problem, compressor starts in first attempt. is this a compressor problem what will happen if i continue to run my ac in this situation. thanks in advance

Reply:

AHA Wagar,

I can't pretend we can really diagnose by e-text Q&A, but if I understand more clearly, you are saying that the A/C compressor starts and runs OK the first time, but after the thermostat is satisfied and stops the cooling system compressor/condenser, when the temperature in the building rises and the TT calls for cooling a second time, the compressor is having trouble starting.

A simplistic view would be to treat it as a "hard starting compressor" and install a hard start capacitor kit. But since the compressor starts OK cold, it might be a different trouble.

If the compressor is trying to re-start against high head pressure that is more difficult than starting "cold" when the refrigerant pressures are the same on both high side and low side of the system.

So I'd look into what would cause head pressure to remain high after the compressor stops running. In many HVACR systems, as soon as the compressor stops running the pressures begin to equalize on the two sides of the system.

For more diagnostic help see the article PRESSURE READINGS, COMPRESSOR (link at Related Topics under the main link heading titled: COMPRESSOR & CONDENSING COIL, A/C

Reader followup:

Hi DanJoe, it even having same problem in first time start and now these days after its thermostat satisfies its not restarting after several attempts. what i am concerned is: is it a compressor problem? or capacitor. or possibly some thing else when ac start it works fine i am as far as cooling is concerned there is no problem with cooling once it get success in starting. - Waqar

Reply:

Waqar why don't you try a hard-start capacitor kit

Reader followup:

Thanks DanJoeFriedman i will definitely try actually i am away from my home town will reach in 15 days. i would like to thanks you for your support you provided and will let u know the results.

Question: start/run capacitor changed, but now nothing works

I changed equivalent capacitor after that it was ok to startup.
Now i need to turn on back, but it di dnot startup. i need to turn off siwtch then tunr on back switch in order to startup again.
Why is it?
Thanks, CHang - 8/26/11

Reply:

I'm not sure, Chang. Double check your capacitor to see that it's matched in rating to the original and that you wired it correctly.

Question: outside fan won't run, A/C is making a hissing noise

fan on outside unit does't run the ac runs but does not cool makes hissing noise - Nancy 9/7/11

Reply:

Nancy, See NOISES, COMPRESSOR CONDENSER (article link at Related Topics ) to diagnose various A/C system sounds,

Watch out: If you hear a loud high pitched noise at the compressor, turn off electrical power to the unit immediately.

Other more quiet hissing noises from the air conditioner compressor motor may (if the motor is a reciprocating compressor) be due to leaky internal valves. The compressor motor makes a hissing sound all during the time the compressor is running; when the motor stops the hissing dies down fairly quickly as the high side and low side pressures equalize. In this case the condition may not be dangerous, just an inefficient system that is costly to operate.

Question: air conditioner compressor shuts down after 30 minutes or less

My compressor shuts down after only 30 minutes or less, it starts fine, but cooling seems to be a bit less then before, and none at all once it shuts down. I open the breaker for a short time and it will run again, then shut down. - Darrell M 9/8/11

Reply:

Darrell, it sounds as if a compressor motor may be overheating; when you leave power off for a time the motor cools down enough that its own internal thermal reset in fact resets itself. I'd call a service technician for more thorough diagnosis.

By no cooling, if you mean there is airflow but the air is not cool, that's consistent with above.

Question: the Haier AC unit is forming frost or ice on the coil

my question is i have turned off my 1 ton haier ac its inner unit is shut off but not outer unit due to which it it creates ice in inner unit can you let me know what is the issue. Thanks !! - Asim Niaz 9/15/11

Reply:

Asim, if the indoor blower unit is not running and the outdoor compressor is running the lack of air movement across the evaporator coil will lead to frost and ice formation on the coil. Under COOLING COIL or EVAPORATOR COIL you'll find diagnosis of ice or frost blocked cooling coils.

Question: I filled up my air conditioner with gas but now what?

So what is the solution of this problem as i have already filled gas recently. Thanks !! - Anon 9/16/11

Reply:

You need a service call from an experienced diagnostician. We don't have enough information about your case to specify a fix.

Or take a look at LOST COOLING CAPACITY for more diagnostic guides
(article link is at Related Topics )

Question: replaced air conditioner compressor, new syste is icing up

Question: My air conditioner compressor blew, the new system is icing up, what's going on? add another return to it . may have to change duct size maynot if indoor unit is close to returns . hope that helps a bit - Chris 3/15/12

Reply:

Rooster said:

Sounds like you may have put a 1500HP Blown Hemi in a Volkswagen. One thing to try...did the installer select the proper fan speed for the air handler? If the fan is running in a slower speed (usually for heating, not A/C), air flow will be inadequate. But I'm betting on inadequate duct capacity. Probably should have stuck with the 4 ton evaporator coil. Sounds like an oversight or ignorance on the installers part to me. Also see COOLING COIL or EVAPORATOR COIL for our article on causes of cooling coil ice problems. Something as simple as a dirty filter or blower fan can cause the trouble.

Question: my central AC unit is blowing out black particles

My central ac unit is spewing out black particles. I got the blower and the duct cleaned for my whole apartment, but the ac is still blowing the black particles. Does anyone have any idea what it is and how I can get rid of it. Thanks - Amsa 5/6/12

Reply:

Amsa: about A/C blowing out black debris particles, check for damaged duct insulation, say from a mechanical cleaning operation, and of course be sure you've got a new clean air filter in place; The inspection in the air handler ought to include a check of bearings and moving parts for damage;

Question: My A/C capacitor burned up

My capacitor on my Trabe XL13i burned up along with all the wiring above it into the compressor area, it appears to have caused a fire, because it melted part of the outside of the unit case. Is it worth getting the wiring fixed and seeing if the rest of the machine still works or should we just call it quits and replace it? The air conditioner is 9 years old. - Shana5/16/12

Reply:

Shanna, about a burned up capacitor: it is possible for a capacitor to itself be the point of a failure; I'd try replacing the capacitor and any questionable wiring or connectors; let us know how that works.

Question: no cool air is blowing inside the house but outside compressor unit is running

No cool air blowing inside the house. The fan running outside is blowing cool air not hot/warm air. Not sure if it's a compressor issue. - Orios 5/29/12

Reply:

Orios, if the compressor motor never runs, but the air handler unit is running and the thermostat calls for cooling, the problem is at the compressor / condenser unit. See the diagnostics under "COMPRESSOR & CONDENSING COIL, A/C" (article link at Related Topics )

Question: my 15 year old central air conditioner is running fine but I was advised to replace it to avoid risking refrigerant line contamination if the old compressor fails

I have 15 years old central AC unit. It is working fine. I was advised to replace it with a new one because there is a danger of refrigerant contamination of pipes if the old unit fails. If it happens,
to clean/replace pipes would cost additional 2000 dollars. How serious is it? - Salve 5/31/12

Reply:

Salve I think you should get advice from a different and more experienced HVAC tech. Like many a good lie, this one has some truth in it: if a compressor motor fails, burned oils in the refrigerant can contaminate the refrigeration piping - that's why when a burned out unit is replaced the tech will pull a vacuum on the system, do his/her best to clean the lines, and a special compressor burnout-filter or two will be installed on the refrigerant lines to protect the new motor and other parts from damage or debris clogging.

But a system can fail in a variety of ways, and as I explained there are well known means of dealing with debris in the system. What you were told would make me look elsewhere for my HVAC maintenance and repair services.

Question: My air handler works but the outside AC unit doesn't come on all the time - bad compressor?

my air handler works, but the outside ac unit does not come on all the time. It's intermintent. My HVAC guy did pressures and said I have a bad comprresser (20 year old unit) and I'm better off getting a new ac unit. Sometimes it will come on and stay on. Other times it will not come on at all. - JPI 6/16/12

Reply:

JPI, I'm in no position to second guess the expert who was on the scene - s/he sees clues and performs test way beyond what we can do in a text Q&A. But here are some thoughts:

a failing compressor motor can become increasingly hard to start; the tech can install a hard-start capacitor to get the motor running again - for a time - and it might be worth a try: that's an inexpensive part and usually fairly straight-forward to install.

Question: 8 year old TempStar Air conditionre troubleshooting

We had a service tech out for a inspection check up of our 8 yr old tempstar unit because we cannot seem to get the the house temp to the low 70s even when unit runs for 5+ hrs strait....
the tech said the coil needed cleaning or replaced and our compressor was not starting and that it was just humming & clicking when trying to start and recommended to us 2 options to remedy the problem...new compressor or new system and both were not cheap.

while he was testing the equip outside I was in my office and could hear and feel the vibration of the unit trying to start...

My son-in-law came over and we removed the coil and cleaned it thoroughly and then checked all the wiring on the outside unit compressor and found a green wire disconnected and stuffed into a hole (Hmmmmm!).
we reconnected the wire and fired the unit up and the compressor seemed to start with no problem ( no humming or clicking).

So, if it is 98F outside we cannot get the inside house temp below 79f,,I put a refrigerator thermometer in front of an air duct and left it there for 30+ minutes and then checked it....it read 61F...I am at a loss of what to do....also the blowing air pressure does not seem to be strong.......what to do??? - Doug S 6/24/12

Reply:

Doug the green wire is probably a ground that needs to be connected, but I'm doubtful that that will fix a humming compressor - more likely the compressor start/run capacitor is bad or the compressor motor itself is bad. It sounds as if there may be some risky do-it-yourself work going on - I'd call a trained HVAC tech at this point.

Question:

THE METERING DEVISE NEED TO MACH CONDENSER IF IS 4 TON SET A 4 TON METERING DEVISE EVEN ON A 5 TON EVAPORATOR. - Anon 7/11/12

Reply:

Agree, though some TEVs can be adjusted within an operating range for most equipment in residential applications

Question:

I am troubleshooting a 7500BTU Danby portable air conditioner (the tall vertical unit with ducting out the back via flexible hose). It appears that the compressor itself is at fault, but I would like to be sure before replacing the unit. The start capacitor measures OK (meaures 46uF for a 45uF +/-5% unit) and appears in good condition. I measured the resistance between the three compressor terminals and they seem to be OK (C-S=2.8ohms, C-R=1.0ohms, S-R=3.7ohms) and there is high resistance between all terminals and ground. I applied 117Vac directly to the compressor (bypassing the control circuits) and the compressor just hums - the current draw was 30A. Being a protable unit, everything is jammed into the compartment and I don't see any way to access the compressor at all. I'm about to give up on the unit and look for a new one, but just wanted to see if there are any other things to try. The unit is probably about 9-10 years old, but has only seen regular use in the summer over the last 3 years.
Thank you for any help or advice.
Mike - 7/14/12

Reply:

I agree with your suspicion about the compressor. Often though a tech will just try swapping in a new start/run cap as a cheap simple test.

Question: air conditioner just blows hot air

air conditioner blowing hot air - Ann 8/4/12

Reply:

Ann,
with just the info you provided - blowing hot air - first make sure your thermostat is set to COOLING mode - and presuming it is and that all of the equipment inside and out are turned on, check

DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP

the article link found at Related Topics - for a starting point in diagnosing why an air conditioner is not working.

Question: split system air conditioner stopped working - electric wires keep burning up at the terminals

My AC split unit stop working ,because the terminal wires connecting the compressor to the capacitor always burn this happen several times ,and the remedy was to replaced the burned wires,please can you advise what the reason that keep the terminal wire burn, the compressor is newly installed, Mohamed al lababidi -8/29/12

Reply:

Mohamed,

If the terminal wires keep burning up I suspect that the problem is one of

- an overcurrent - high amps draw because a motor is seizing and needs replacement - most likely it's this problem

- bad electrical connections, possibly involving alumnum wiring or loose connectors
- improper electrical wiring - such as undersized wires for the length of run, or mis-placed connections
- abnormal voltages in the system or voltage surges

...

Ask a Question or Search InspectApedia

Questions & answers or comments about air conditioning and heat pump compressors: diagnosis, failure, repair, replacement

 

Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' home inspection education products include
  • The ASHI-adopted Home Inspection Training Program, and Commercial Building Inspection Courses
  • The Home Inspection Home Study Course, and publications such as
  • The Home Reference Book, a reference & inspection report product for building owners & inspectors.
    Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a ten percent discount on any number of copies of the Home Reference Book purchased as a single order. Just enter HRBUS10 in the order payment page "Promo/Redemption" space. Note: InspectAPedia.com ^® editor Daniel Friedman is a contributing author.
  • The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones
  • Home Inspection Report writing materials, including the Horizon Software System that manages business operations, scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
  • The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors
• Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
  
• Thanks to Scott at SJM Inspect for suggesting this EPA document and for technical editing remarks regarding our air conditioning website, SJM Inspection Service LLC, serves the entire state of CT, sjminspect.com 203-543-0447 or 203-877-4774 5/16/07
• Thanks to Diaz, Domingo I. CIV NAVAIR Bldg.2118, rm. 131: domingo.diaz@navy.mil - Ming Diaz, Great Falls, MD for editing help with the text about discharging air conditioning compressor capacitors - 3/07 DF]
• Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
• John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
• Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
• Air Diffusion Council, 1901 N. Roselle Road, Suite 800, Schaumburg, Illinois 60195, Tel: (847) 706-6750, Fax: (847) 706-6751 - info@flexibleduct.org - www.flexibleduct.org/ -
  "The ADC has produced the 4th Edition of the Flexible Duct Performance & Installation Standards (a 28-page manual) for use and reference by designers, architects, engineers, contractors, installers and users for evaluating, selecting, specifying and properly installing flexible duct in heating and air conditioning systems.
  Features covered in depth include: descriptions of typical styles, characteristics and requirements, testing, listing, reporting, certifying, packaging and product marking.
  Guidelines for proper installation are treated and illustrated in depth, featuring connections, splices and proper support methods for flexible duct. A single and uniform method of making end connections and splices is graphically presented for both non-metallic and metallic with plain ends."
  The printed manual is available in English only. Downloadable PDF is available in English and Spanish. 
• Owens Corning Duct Solutions - www.owenscorning.com/ductsolutions/ - provides current HVAC ductwork and duct insulating product descriptions and a dealer locator. Owens Corning Insulating Systems, LLC, One Owens Corning Parkway, Toledo, OH 43659 1-800-GET-PINK™
• "Flexible Duct Media Fiberglas™ Insulation, Product Data Sheet", Owens Corning - see owenscorning.com/quietzone/pdfs/QZFlexible_DataSheet.pdf
  "Owens Corning Flexible Duct Media Insulation is a lightweight, flexible, resilient thermal and acoustical insulation made of inorganic glass fibers bonded with a thermosetting resin."
• [1] "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author].
  Warren Hilliard was an HVACR instructor as well as operator of an HVACR repair company in Dutchess County, New York.
• [2] Christopherson, Norm, "Preventing Premature Compressor Failures, An Ounce of Prevention for Years of Service", web search & reader TN Goose referral, 08/12/2011, original source: http://www.hvacfun.com/a-once-prevent-years-service-comps.htm
  Quoting: Norm Christopherson, CM, is a long-time hvacr instructor at San Jose City College, San Jose, CA
• [6] Determining Compressor Amperage Ratings, Joe Marchese, Air Conditioning, Heating, Refrigeration News, 31 July 2003, web search 08/12/11, Joe Marchese is owner of Coldtronics of Pittsburgh. He can be reached at 412-734-4433, www.coldtronics.com, or joe@coldtronics.com. Original source: http://www.achrnews.com/Articles/Feature_Article
  /c229b8960ac5a010VgnVCM100000f932a8c0____ - quoting:
  

Books Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author. Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

• Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
• Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
• "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
• Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
• Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
  
• Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard
• Asbestos HVAC Ducts and Flues field identification photos and guide
• Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation

...