Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked. A/C &Heat Pump Compressor/Condenser Repair FAQs
Q&A on how to diagnose, repair or replace the compressor/condenser

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Air conditioner compressor unit diagnosis & repair Questions & Answers:

These FAQs about the diagnosis or repair of the compressor/condenser unit assist in understanding what's wrong with the equipment and what to try next.

This article series discusses the outdoor components of air conditioners and heat pumps: how the air conditioning compressor-condenser unit works; the detection of defects in air conditioning compressor and condensing units, 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.

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Air Conditioning Compressor / Condenser Repair FAQs

Schematic of an air conditioner compressor unit showing inspection points (C) Carson Dunlop Associates

These questions & answers about repairing an air conditioner or heat pump compressor/condenser unit were posted originally at COMPRESSOR / CONDENSER REPAIR - you will want to review that page.

Our sketch of the condenser unit shown here was provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing company. [Click to enlarge any image]

On 2017-06-06 by (mod) re: A/C compressor cycling on and off


At OPERATING DEFECTS, AIR CONDITIONING we list the common operating problems and suggest sequences of diagnosis and repair steps for them.

But cycling on and off at the A/C or heat pump compressor is not addressed.

Diagnosis depends in part on the "on and off" frequency and regularity, and also on whether the problem is a recent one or one that has been present since the system was installed.

if the unit has always cycled as you describe we could be looking at an oversized thermostatic expansion valve - that causes a "seeking" behaviour that will cycle the system with some regularity

If the problem is new and the compressor cycling is frequent but irregular I'd look fist for a loose wire or loose or corroded connector, then for a failed control relay or control board.

On 2017-06-06 by asif

Compressor is going on and off

On 2017-06-06 by (mod) re: ran A/C with cover on


The concerns about running an A/C unit with the cover on would be around problems with overheating. Details are at AIR CONDITIONER COVER USE.

On 2017-05-06 by Mark

my air conditioner was run accidently with the cover on. What kind of problem will that create? and how best to diagnose?

On 2017-04-29 by Anonymous

RLA for compressor is 13.44 i checked while running and it shows only 4.4 amp , is it compressor broke ?

On 2016-12-13 05:28:59.001907 by J

I have a Heil heat pump (8 years old) and the fan turns on for thirty seconds then off for five and continues to repeat this process over and over.

On 2016-09-21 00:04:25.372076 by karen

even when i turn off inside unit with remote outside unit continues to run?

On 2016-09-14 by (mod) re: icing on the suction line

Typically you see icing on the compressor itself and on the suction line remote from the cooling coil when there is low refrigerant in the system or when the refrigerant metering device, cap tube, or TEV or EEV is not working properly.

On 2016-09-14 06:42:50.001212 by bebesotek

why compressor and suction piping became icing ? LP = 55psi HP = 250psi

On 2016-07-04 03:42:24.384565 by (mod) re: compressor can't start: bad capacitor?

Possibly a bad capacitor;
Try turning off the system for 45 minutes or longer;
Then see if it can re-start.

On 2016-07-04 by Barry

Our heat pump stopped producing cold air. The outside evaporator fan runs and I hear the compressor trying to start. Would a capacitor be bad?

On 2016-06-22 by Anonymous

What is to check, its 50hz not 50/60hz. Somebody told me it will not give me as much cool as it suppose to be. Is it correct? I thought 60hz will make compressor to work faster, not slower?

On 2016-06-22 by (mod) will a mini split work on both 60Hz and 50 Hz power?

Check the manual and data tag. Often yes.

On 2016-06-22 01:28:35.297625 by Anonymous

Would 220/50hz mini split unit work with US 220/60hz apartment?

On 2016-06-04 by (mod) bad contactor or loose wire & other causes of a cycling A/C compressor

It could be the contactor relay or a loose wire or a bad sensor, or a sticking TEV or something else.

On 2016-06-03 by jason

when a condenser fan and compressor keep going off and on,Is it the contactor that is bad?

On 2016-06-04 by (mod) fan motor turns on but doesn't spin

The AC fan motor could be seized - is it humming? If so turn it off.

Or the motor may run but the fan is loose on the motor drive shaft

On 2016-05-27 by joseph re: fan motor won't rotate

what could be the problem of our carrier window airconditioner, the fan motor turns on but it does not rotate?

On 2016-05-26 by roberto zarate

how look a 24v coil in split system air condition

On 2016-05-18 09:51:23.911808 by Anonymous

Does the water from compressor base comes when AC in use..?

On 2016-05-08 by (mod) re: I was told a chipped reed valve cannot br repaired or replaced


What you were told is correct. A/C or heat pump compressor motors are a hermetically sealed unit: the motor and components are in a "can". It is not possible to repair parts inside the unit. The repair is to replace the compressor motor; there are perhaps other reasons why your repair person wants to replace the entire compressor/condenser unit instead.

On 2016-05-08 by Peg

I was told a chipped reed valve cannot br repaired or replaced, so I require a whole new condenser. I've been unable to find information here about repair or replacement of reed valves. Please help me find the answer. Thanks!

On 2016-04-28 18:29:33.992824 by Anonymous

How to maintain level cooling tower

Y did codenser tube in used

On 2016-04-17 by (mod)

Sorry, I don't understand the question

On 2016-04-17 by heat falling air in blower inside the room

heat falling air in blower inside the room

On 2016-02-12 by (mod)

Rick, Sorry I don't understand the question. Compare the fusing size to the recommended fuse amperage on the data tag of your unit. Check for power on the circuit. Check for burned aluminum wiring on the circuit. Leave power off.

On 2016-02-12 by rick

Exchange air handerler fuse to a 20.amp an unit stopet after 2 days

On 2016-01-09 by (mod) re: how much ice on the cooling piping is OK

A small amount of ice on a refrigerant piping close to the unit is common and OK - (insulate the line); if the coil is icing then the unit won't keep working properly - that is in heat pump mode it won't provide heat to the home. A cause could be low refrigerant or a refrigerant metering valve that is not working properly. IN that case call your sevice company for repair.

On 2016-01-09 by Anonymous

I can't seem to find my questions in the Inspectapedia. I have ice build up on my outside compressor unit. It is working fine and the temp. outside is about 28 degrees. Should ice be forming around the unit?

On 2015-11-13 by (mod) re: loud noise when compressor condenser starts up

Not sure, Brandy. Perhaps a damaged compressor motor or a blowing fuse.

On 2015-11-13 by Brandy

What would make you outside unit make a loud noise when you first turn your heat on in the winter

On 2015-09-17 by chris

I tested the heat on my unit the other day worked fine the aux. Heat worked fine. Turned on the air today and the air wasn't cool I checke the outside unit and the coils were hot like the aux Heat was stuck on. What would cause this the thermostat inside didn't say it was on

On 2015-08-18 by (mod)

Terri I can't diagnose the vibration from just your email - it could be serious, such as a failing compressor, or something simpler like a loose fan or even just loose hardware. I'd ask for help from a local service tech as by making a repair you may avoid more costly damage.

On 2015-08-18 by Terri

We rarely need to run our air conditioner but recently had a heatwave. On the third day of running it a fairly loud vibration noise started. It was coming from the outside unit. We turned the air off at the thermostat then turned it back on after about one half hour. It would run fine then after a period of time the vibration would start again. I'm hoping it's an easy fix.thank you

On 2015-08-17 by (mod)


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On 2015-08-17 by princely

your page has been helpful with hint on how to fix it yourself. i intend starting a diploma program in Refrigeration and Air conditioning. please I would like to have a pdf copy of the entire air conditioning section for educational/personal improvement purpose; my email is thanks alot

On 2015-06-10 by (mod)

Donna I can't diagnose this from just your e-text; no one would, however, be able to patch a refrigerant leak with an external black gummy substance that I know of. More likely that's something else, perhaps sealing an opening where tubing passes or replacing damaged refrigerant tubing insulation.

IF your unit has lost refrigerant, indeed there is a leak to find and fix. Do not waste money by repeated re-charges of refrigerant (nor do we want to keep dumping refrigerant into the environment).

Surely the new work was warranted, right?

On 2015-06-10 by Donna

We had our air handler replaced just about 1 month ago but not the out side unit! I was surprised because the unit out side and in were put in when the house was bui!t in 1997. There was a freon leak in the unit inside. I was told there was no leak outside but there is a blue gummy substance where it looks as if the tried to patch a leak!

So why would someone not deem the whole system shot and replace the whole unit! Cause I seat here now with a non working unit again after dumping more than 800.00 into the unit on the inside and no freon in the unit yet again!

On 2015-05-29 13:45:14.084950 by Anonymous

I have a UPG Coleman 14.5 SEER 3 ton split unit. Unit is less than 3 years old. It runs almost all the time and the temp coming out of the registers is about 68 to 70 degrees. Return air is about 75 degrees. Coils are not iced up. TXV and reversing valves have been replaced. If set on 72 degrees, the temp goes up during the day to almot 79 degrees when 90+ outside. Unit is not producing cold air to keep a constantly cool temp inside. What is wrong with my unit?

On 2015-04-13 21:30:57.716140 by (mod)

Thank you Anil. We also welcome questions, critique, or content suggestions. Working together makes us smarter.

On 2015-04-13 20:32:50.878590 by ANIL KUMAR

Working of referent components is easily understandable . It is really good for beginners . Excellent.

On 2015-03-01 17:45:04.793430 by (mod)

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies,

Question: Is the problem with the fan motor or the compressor motor in my condenser unit?

I've a Lennox outside a/c unit. The fan/motor and compressor are part of the unit. The fan was not spinning and the A/c is not running. I've isolated the problem down to the fan/motor or the compressor, but don't know how to check or find out which it is. Any idea on how to check if the fan/motor is 'bad' or the compressor is 'bad'? - Fan or ... 7/23/11


Fan or compressor: you could also have a bad control board, or relay switch in the compressor/condenser unit. If the fan is bad and the compressor is OK you'll hear the compressor turn on at the start of a cooling cycle, though a bad fan and system overheating could later cause some compressors to turn themselves back off. Similarly, if the compressor is bad your fan motor would still run. So I'm suspecting a control or switch problem./

Question: Icing at the compressor; compressor not turning on?

the outside unit of the heat pump is icing up on the compressor - Steve 8/7/11

Hi my fan in my house goes on but my compressor unit does not all the electric seems to be fine . could it be my thermostat? - Sam 8/7/11

the accu very heat,although it is new gen. clean,2Tr LS-60psi & HS-100psi, - Anon 8/6/11


Steve: icing at the compressor/condenser sounds like a refrigerant charger or refrigerant metering problem.

Sam: if your thermostat turns on the air handler but the compressor/condenser does not run, the problem is not the thermostat. Check out the diagnostic suggestiosn beginning at LOST COOLING CAPACITY (link at the "More Reading" links at the bottom of this article )

Anon: those pressures look kind of low, no? What does your HVAC tech say about normal for that system?

Question: My A/C compressor just won't stop running

I recently noticed my AC condenser unit still running when the system inside shutoff by itself. and also, does the condenser unit have to be leveled. I notice the slap which holding the unit is slopping. Any suggestions? Thank you. - Rick 8/16/11


A/C compressor/condenser won't stop running:

Rick usually when an A/C condenser unit won't stop running even though the inside equipment has shut off by itself my thinking divides into two investigations:

- is there a problem with the INDOOR unit such as a blower fan that won't start, an access door switch open, a condensate drain switch turning off the blower unit - these can leave the system calling for heat and the compressor running (though that's not good for the compressor)

- is there a problem with the outdoor equipment such as a bad control relay or control board

Question: loud cricket chirping sounds at the compressor/condenser unit, and slow starting

outside unit making loud cricket sounding noise when running. Takes long time to come on when temp set low. - JT 7/276/12


JT our link at the "More Reading" links at the bottom of this article NOISE AIR CONDITIONER / HEAT PUMP provides noise diagnostics.

About taking a long time for the A/C to "come on" when the temperature is set low: the thermostat is operating like an "on-off" switch that turns the air conditioner system on and off in response to room temperature. It's not an accelerator. So if there is an operating problem related to the system controls, the number of degrees below the room temperature to which the thermostat is set should make no difference in how long it takes the A/C system to start. As long as the SET temperature is lower than the room temperature the cooling system will turn on.

Question: how long should the AC run when first turned on

Anon said

when you turn on the AC for the first day of summer or heat how long would the unit circulate air then when does it stop


The length of time that the A/C will run depends on many factors including

- the thermostat set temperature
- the building temperature at time the A/C is tuned on
- the efficiency of and cooling power (BTUS) of the system
- where the air is delivered
- thermostat location
- the thermal mass of the building: what materials have been heated up and need to be cooled down
- the heat gain rate of the building
- outdoor temperature, wind, and sun exposure

The air will circulate and the A/C will run until the thermostat is satisified. If the system cannot satisfy the thermostat for any reason the system will keep running.

Question: water at the base of the compressor

(June 30, 2014) Anonymous said:

Is it normal for there to be water coming out of the base of my compressor



Water at the outdoor compressor condenser is probably coming from melting ice or frost. If you see cycles of significant ice or frost build-up the refrigerant charge or metering may be incorrect and I'd ask for a check by an HVAC tech.

Question: Compressor won't start

(July 13, 2014) Anonymous said:
i have a Carrier heat pump that i cant get the blower to come on. I have replaced the board and thermostat and not sure what to do next. Any suggestions?

(Aug 2, 2014) Lou said:
I have a carrier condensing unit that the compressor wont start.I have voltage at the contactor and have replaced the start cap and run cap.odd to say,im drawing 11 amps on start and run wires coming from the contactor but i hear nothing from the compressor! any suggestions?



Check for a bad start relay

Question: compressor won't run until it's cooled down

(Aug 14, 2014) Andre Matthew said:
my AC is not cooling well don't know the problem with that.

(Aug 21, 2014) Wayne said:
When unit is cold it will start and run. After an hour the cooling fan stops but the compressor continues for a short time then quits. It will continue to start but will not start and run until it cools down.
Any ideas?


Look for an overheating fan motor, relay or control board or possibly a refrigerant metering valve that is sticking


Continue reading at COMPRESSOR / CONDENSER REPAIR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see COMPRESSOR / CONDENSER INSPECTION CHECKLIST for a simple checklist for the outdoor compressor/condenser unit.

Or see DIAGNOSTIC GUIDES A/C / HEAT PUMP - suggestions for diagnosing compressor or condenser fan and coil problems that can mean intermittent or totally lost cooling capacity of your system.

Or see COMPRESSOR FAILURE DIAGNOSIS - Initial, simple diagnostic checks of the air conditioning compressor are also described

Or see this

Article Series Contents

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COMPRESSOR / CONDENSER REPAIR FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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