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This Air Conditioning Troubleshooting & Diagnosis FAQ (list of frequently asked questions about air conditioners) lists
the major areas of investigation to be followed in diagnosing all types of problems with air conditioning systems and heat pump equipment.
Typical air conditioner concerns include compressor or blower assembly noises, failure of air conditioners to start or to keep running,
inadequate cool air flow or air quantity, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply,
or even loss of air flow entirely.
Also discussed are various electrical wiring, fusing, overcurrent, and thermostat or control defects
on air conditioners.
The air conditioning system will not operate at all: power may be off, controls may be improperly set, or the system may be inoperative. (Confirm that the system has electrical power and that all of its control switches and thermostat are set to on and cooling positions.
see CONTROLS & SWITCHES
The air conditioning system operates but does not produce cool air, or not enough cool air.
see LOST COOLING CAPACITY
The air conditioning system operates but there is not enough cool air flow at the registers.
see DUCT SYSTEM DEFECTS.
The compressor was short-cycling, that is, turning itself on and off rapidly, perhaps every few seconds or minutes rather than producing a normal on-cycle of 10 minutes or longer.
see COMPRESSOR CONDENSER
The compressor was noisy, during startup, indicating an operating problem.
see COMPRESSOR NOISES.
The compressor squealed at startup, indicating that service may be needed promptly to prevent possibly costly damage to the system. This repair/maintenance item should not be deferred.
see COMPRESSOR NOISES.
Inside cooling or evaporator coil defects that can be seen by eye: dirty coil, blocked coil, frost on the coil, improperly sized evaporator coil, improper evaporator or cooling coil placement in the system.
see AIR HANDLER / BLOWER UNITS.
Air flow across the air conditioning evaporator coil: if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty
blower squirrel cage fan), the air conditioning system will not operate properly.
Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity.
One ton = 12,000 BTUH so if your AC unit is a 24,000 BTUH unit it is a "two ton" unit and needs to see 700 to 800 CFM of air across the evaporator coil.
Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy.
The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.
Evaporator coil cleaning often requires cutting refrigerant lines, removal of the coil and other components for cleaning, and reinstallation, pulling a vacuum on the refrigerant lines, and recharge with refrigerant. Such service and repair may involve significant expense, although there are some "in place" cleaning methods using foams and sprays that are a simpler procedure.
See DIRTY COIL CLEANING PROCEDURES, FROST BUILD-UP on AIR CONDITIONER COILS and OPERATING TEMPERATURES.
Dirty air conditioning filters, - a source of increased operating costs. Very dirty filters can eventually block the fan itself, leading to more costly repairs. The filters should be changed monthly when the system is in use. Failure to properly filter dust from the return air supply can load the fan or evaporator coil with dust and prevent proper system operation. Installing a filter is normally a minor expense. Dirty, blocked evaporator coils can result in improper system operation, very low output temperatures, low air flow (compensated sometimes by increased fan speed), and sometimes frost on the coil and failure of system components.
See AIR FILTERS for HVAC SYSTEMS, and also AIR HANDLER / BLOWER UNITS. See OPERATING TEMPERATURES.
The air conditioner fuse keeps blowing or the circuit breaker trips: could mean a compressor which needs repair or replacement, or it could mean a problem with the unit's electrical wiring, such as use of aluminum wiring combined with bad electrical connections. Have your service technician check the condition of the electrical circuit first (that's cheaper than a new air conditioning compressor) and then check the condition of the compressor.
see COMPRESSOR CONDENSER for air conditioner compressor diagnosis and repair; and if your air conditioning system electrical wiring is aluminum, review the aluminum wiring hazards at ALUMINUM WIRING HAZARDS & REPAIRS since a serious fire hazard could be present.
LOST COOLING CAPACITY explains how to diagnose & repair an Air Conditioner system which has lost cooling capacity
OTHER AIR CLEANERS - how effective are other air cleaners such as free-standing air purifier units? Are some of them dangerous? Maybe. Are claims exaggerated? Usually.
CLEANING & Legionella BACTERIA how to remove or prevent bacterial growth in air conditioning systems, cleaning condensate trays, cooling towers, use of chlorine, bromine, disinfectants in air conditioners
How to diagnose and fix an air conditioning system that is not working
Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply,
or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or
air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.
If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
The motor checks ok no ohn reading on each leg of 110v side of motor, capacitor has ohms of resistance no swelling. Either the mother board or the relay.
With power off, check first for shorted electrical wiring, next for a seizing motor or a motor with a bad start capacitor.
Question: AC blower short cycling on-off betweeen heating and cooling
(July 29, 2011) Charles Gullette said:
I recently had a new 3 ton 13 seer unit installed. It included a new compressor, condenser, and cooling coils and digital non programable thermostat. The existing 3 ton blower and heater unit were reused.
After installation the blower unit starts, runs about 15 sec and then restarts. there is no effect on the compressor unit. My tech. says the blower is starting on the heater relay and then shifting to the cooling relay on the blower control board. He claims this is not a problem but that the board may need changed in the future. I did not have this problem prior to the new unit installation. Could it be the thermostat wiring or is my control board going bad??
Charles, I wonder if the new thermostat was wired exactly the same as the old one? And I agree that the circuit board could otherwise be the problem. I also agree that it's curious to have to change a circuit board after other components were swapped out unless either there is a compatibility issue (sounds wrong) or an accidental short circuit, or some mechanical disturbance that just pushed a failing component over its edge.
Question: AC making revving up sounds
(Aug 27, 2011) AC making "revving up" sounds ev said:
When my AC (Trane) is running is sounds like someone is revving an engine every few minutes. The indoor part of the system is in the attic and when the "revving" noise happens the sound below, in the house, is like a "Blue Northern" strong wind.
Any thoughts? Thank you! NF
Singer incremental under window electric unit.
Compressor over heated and has seized. Tried Super Capacitor with no effect.
Replaced compressor. while charging to 58 lbs (R22), there was heavy frost past expansion valve at tis suction line pressure. No sweating of suction line. Compressor overheating. Changed filter/dryer installed a few years earlier. Retested. No change. Resting pressure was 250 psi. Changed expansion valve for new one. Much less frosting, but still evident at 58 lbs pressure after recharging. Now has new compressor, filter/dryer and expansion valve. No other components to change other than C coil. What's going on?
Dave, contamination may be fouling the TEV causing it to open or close erratically.
Question: air conditioner turns off without cooling down the house
(July 12, 2014) Anonymous said:
My central air will go on than turn off in about an hour without cooling house down to set temp. There's a new motor, fan and pump.
question:jus changed the circuit board in my system...everything seems to be ok
except tht im not getting temperature control...checked room temp. using 2 different
thermocouples from digital meters...room temp stabilises at 20 degrees..upping set
temp.to 28 degrees and compressor keep
s running...temp.records at 20degrees on both meters..possible problem...can it be the evaporator sensor?
Anon I'd start by checking the temperature drop across the cooling coil
Question: AC Died, Now Runs Intermittently
(Sept 24, 2014) AC Died, Now Runs Intermittently After Repair ? said
AC died in the middle of this horrendous hot spell. Ended up changing the compressor/fan capacitor and the contactor circuit board. Unit fired immediately when turned on and was putting out cold air. Unfortunately it will run for a couple of minutes then it shut down and will not restart until it sits for awhile. Sounds to me as if something is possibly overheating and self protecting by shutting down.
From just your note, AC, I can't make a useful guess. It's time to call a trained HVAC technician. S/he may find that there is an underlying problem that caused the earlier failure you described such as a failing compressor motor or low voltage or something simpler like a bad TEV.
Question: Whirlpool Room Air Conditioner model WS092LW circulates hot air
(Oct 7, 2014) Joe Rouse said:
I have a Whirlpool Room Air Conditioner model WS092LW. Even if Whirpool no longer sells this model, where can I get info on the unit? Mine is moaning and ciculating HOT air! Suspect it's in need of coolant, but open to insight on this.
Joe, your AC unit may have indeed
lost refrigerant. Don't just add more without also finding and fixing the leak.
Question: getting heat in cooling mode
12/4/2014 Anonymous said:
when I turn on my ac instead of cooling the heat comes on. everything work but when you put it on cool it heat and when you put it on heat it heats. is it my thermostat inside or something in the heat pump outside?
Anon if you are sure your thermostat switches are correctly set then I suspect a wiring error or a control board failure.
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"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]
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