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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 DIAGNOSIS & REPAIR
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
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
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
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
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 GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
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
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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 DMMs VOMs SAFE USE OF.
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 for shock hazards or equipment damage: see DMMs VOMs SAFE USE OF.
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 there is (probably) no break in the wire or circuit being tested.
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.
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 DMMs VOMs SAFE USE OF. 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
Continue reading at CAPACITORS for HARD STARTING MOTORS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
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.
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
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
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
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
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
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
Linda: you are describing the indoor air handler unit for your air conditioning (see the article link at the "More Reading" links at the bottom of this article titled BLOWER FAN OPERATION & TESTING]
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
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
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
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
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 the "More Reading" links at the bottom of this article 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
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
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.
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
Cindy check out the diagnostic article titled DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP (link at the "More Reading" links at the bottom of this article ) 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
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
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 the "More Reading" links at the bottom of this article )
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
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
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.
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
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
Waqar why don't you try a hard-start capacitor kit
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.
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
Nancy, See NOISES, COMPRESSOR CONDENSER (article link at the "More Reading" links at the bottom of this article ) to diagnose various A/C system sounds,
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
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.
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
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
You need a service call from an experienced diagnostician. We don't have enough information about your case to specify a fix.
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
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
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
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
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 the "More Reading" links at the bottom of this article )
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,
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.
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
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:
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....
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.
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
Agree, though some TEVs can be adjusted within an operating range for most equipment in residential applications
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.
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
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
Question: zero resistance test on AC compressor wiring
(Feb 11, 2014) Jerry Walch said:
I have always thought of this site as providing accurate information and have used it as a reference when writing technical articles. I'm having second thoughts. This (Zero resistance: If there is zero resistance the winding is open or broken) mistake appears in this article on How to Diagnose & Fix a Burned-out Air Conditioning. Zero resistance indicates a short circuit not an open circuit.
You are quite correct that zero resistance means a connection is made and good, not open and broken' infinite resistance would indicate an open circuit. We've published nearly five thousand technical articles and are grateful for careful readers who occasionally find and help us fix a mistake. I trust that an error that slipped by in an article would not be enough to toss out the work of our many editors and contributors.
We welcome content critique, corrections, or suggestions by this comment form or by email. I have corrected the text, added a warning, and would welcome further comments. We've included a thank-you to you in our References section at the end of this article, keeping your ID private - let us know if you want to be identified by name in that part of the document. Thanks again,
Question: AC compressor dead short to ground - rusty start capacitor
(Mar 7, 2014) Ricky Thompson said:
I recently had a compressor failure on my homes heat pump, the warranty sent a rookie out to inspect it. When the repair man shows up he asks me what kind of system I had, i told him a Trane heat pump. He then tells me he knows nothing about HP's.
Anyways he tells my warranty company that the start capacitor is completely rusted which is untrue it is rusty on top but surface rust, he also tells them that lady bugs and spider webs shorted out my board and tells them and improper installation of the cover let the water in to rust the cap. The cap tests fine, will this cause my compressor to short out?? The compressor is dead short to ground.
Ricky I'm not sure about your message, but in general if a compressor measures as dead shorted to ground it's time for a new one; the compressor motor windings might burn out if the unit could not start because it lacked a working start capacitor. I'm curious about the capacitor test involved; in any case the compressor windings could short independent of the capacitor status as well.
Question: causes of repeated AC or heat pump compressor burn-out
(June 1, 2014) Voscar said:
I got unit complit burn, all the wire, contactor, i rewire the all. But i notes at list that is the 3'time happens. Firts time i believe the 30 amps breaker never open because, i can. See one left was burn in the electrict box. Somebody put two separate breaker each 20 amps. Is how i finded. I revomed does breaker instead i put only one of 30 amps.
This time the breaker wont open. But the main breker outside open, only one side i still got only 120 in the place instead 240. I disconect the unit sistem. To fixed that. Why only would open the breaker in one side. Not complit.
Repeated compressor burn-out certainly means that there is another problem with the system that has not been found.
In addition to the burned out compressor you have faulty circuit breaker(s) that need to be replaced: tell me the circuit breaker and panel brand and I can comment further.
But the compressor burn-up is probably not caused by the circuit breakers but by an operating problem in the system - improper charge, setup, or control board. Possibly low voltage or a start capacitor problem.
Question: how do I know if a new AC or heat pump compressor is really needed?
(June 3, 2014) Dana said:
I have a 22 yr old 3 ton Goodman unit at my home in Dallas, Tx. It recently stopped cooling the house although the inside fan & outdoor unit seemed to be running fine. There was some cool air blowing inside but not enough to cool the house & temps inside kept increasing.
Didn't seem to be blowing as hard as normal thru the inside vents either. Turned unit off since it was doing no good anyway & to prevent possible additional damage.
Nothing was iced up on the outside unit and there was no moisture on visible lines. Prayed it just needed a Freon charge since I had just cancelled my AHS 1 month prior(Murphy's Law!). Friend hooked me up with a friend of theirs who works for AC company but moonlights on the side since I'm presently out of work. Guy comes out, tests something on side of house that is connected to outside unit then opens the side of the unit, tests a few things with a metering device & immediately says my compressor is shot. Shows me a wire running from compressor that is burnt up on the end as evidence.
I read that a clanking noise is a sign of compressor going out & it has been making a clanking noise for a while. Guy recommended replacing entire unit as the most cost-effective way to go since replacing the compressor, cleaning coils, etc would be almost as much as new unit. Said he can get the new unit with his discount for approx. $1,000 & will include warranty. Is he taking me for a ride or does he sound legit? Thanks in advance for your feedback!
(June 19, 2014) ken said:
bad compressor on 22 year old unit should i replace entire outside unit or just the compressor
From what you describe I think the that you probably do need a new compressor/condenser unit.
Thanks! That's exactly what I did =)
Question: shorted, melted wires on Goodman AC unit
(June 19, 2014) Nick said:
I also have a Goodman central air unit. It was running fine but the wires going into the compressor corroded and shorted and melted the compressor terminals. My plan is to replace the compressor. Do I have to worry about burnt freon? And also my model H23B223ABCA compressor is obsolete. There is a replacement for it but do you know if I will have to change any of the plumbing? Or should it be pretty much plop it in kinda thing? I plan on having a tech doing the work.
Question: loud compressor noises
(July 5, 2014) dan said:
my heater started making a loud noise while the air conditioner was running , the air unit stills runs but no air comes thru the vents and the heater makes all kinds of noise
Watch out: I would TURN OFFall electrical power to the system promptly to avoid further damage or hazards.
It sounds as if the blower assembly is damaged.
Question: circuit board replacement on AC unit, now compressor needed
(July 14, 2014) Wendy said:
Second repair call in a month. First, not cooling--a board needed replaced, no additional freon added. Now HP compressor has a short and needs replaced. Trying to determine if it is better to replace entire outdoor unit. What are the chances that other components were damaged due to whatever caused this short before the unit started popping the breaker, whether from a power surge or attempting to run without enough freon or whatever?
Indeed the compressor is such a large part of the cost of the compressor/condenser unit that often it makes sense to replace the whole unit of an older installation. But we'd be more comfortable with some report on the cause of the compressor failure. For example a power surge may indeed have damaged other controls & parts.
Question: AC runs but air not cool at all registers, "blown to ground" (i.e. a short circuit)
Aug 8, 2014) Jennifer said:
Hi. My AC was running but not blowing at every vent and air was cooler on some vents then others . Technician saw ice and then came back and did a leak test and found no leaks. Then AC worked for a day but began to turn on and off periodically . Technician came back out and AC compressor turned on and off while he was here.
He put a booster on it and cold water because it was hot and then tested something and said it was blown to the ground. Home warranty won't pay for blown to the ground diagnosis. But it wasn't blown to the ground initially....right? Just trying to figure out if this makes sense or if warranty company is trying to get out of it. Thanks for your time.
If the evaporator coil is icing over the system is not operating properly and may be low on refrigerant ( a leak someone has not yet found) or may have a failing refrigerant metering device.
Iced over coils can indeed also reduce air flow - but ALL of the air flow would be reduced not just air at some registers.
So I'd also look for open, loose, leaky, disconnected ductwork.
I have no idea what was meant by a "booster" added to the air conditioner, I don't know what "blown to the ground" means, but that sounds a bit like a short circuit and maybe the addition of a start capacitor to a compressor motor.
IF the AC compressor motor is not starting normally it may be damaged, at or near end of life.
Question: why does a blown compressor motor burn out wires?
11/13/2014 Deddy said:
About compressor burn out, i have outdoor unit Daikin VRV III RXQ16PAY1 and the compressor was burned out at cable lug compressor. how can it possible happen? (sorry for bad english)
Deddy, a failing compressor motor can draw very high current (Amps) that in turn can certainly show up at a wire connector.
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