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.

Air Conditioning Compressor / Condenser Repair FAQs

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.

Condenser fan sounds like a helicopter and is getting louder

My heat pump outdoor 2 blade condenser fan sounds like a helicopter and is getting louder - On 2019-12-18 by Tibor -

Reply by (mod) -

Tibor

See NOISES, COMPRESSOR CONDENSER

also, in the ARTICLE INDEX you'll find our article series on NOISE DIAGNOSIS that describes various sounds coming from heating and air conditioning equipment and the usual causes. That would be a great place to start. Don't hesitate to ask questions.

mon compreseur sali 10minit es saret 30minit

mon compreseur sali 10minit es saret 30minit - On 2019-08-13 by cheikh -

Reply - by (mod) -

You might try the search box above to find our article on

THE COMPRESSOR/CONDENSER TURNS ON & OFF TOO FREQUENTLY

Refrigeration unit fan not working

hi sir
i have samsung refrigerator model RS22FLMR that has problem
first the condenser fan (12 volts)n ot working ,,i replace it still not working ,

i replaced it with a 220volts fan it works good but the compressor start once when i powered the refrigerator on than wont start again until I un-plug and re-plug in the power cable so he start once again
what should i do plz

is it becose of dc 12 v fan not connected to board so compressor wont start again? or board problem or what u think about that . - On 2019-05-21 by Farid -

Reply by (mod) - high head pressure: compressor can't start

Farid

When a compressor motor has trouble starting in the manner you describe I suspect a refrigerant metering device clog - such as a clogged cap tube.

If the compressor is facing high head pressure on its outlet side it can have trouble starting.

On 2018-10-19 by jozef - sta bih moglo biti t.j. sta dalje da se radi? - Croatian HVAC

say the mehanical it|s comresor is die,not me posible starting compresor end stop ,two min work end shake...,w is this?

...sta bih moglo biti t.j. sta dalje da se radi?

klima 12 LG spoljna jedinica ,zamenjen kondenzator,upali krene sa radom i stane,protrese se na swakih two min.

On 2018-10-19 by (mod) - signs of over-pressure in an A/C or heat pump compressor system

Jozef

regarding your question:

Air conditioning 12 LG outdoor unit, replaceable capacitor, inflammation starts and falls, shakes on swaps for two min.
What could i be t.j. is it still to be done?
...
say the mehanical it's comresor is die, not me posible starting compresor end stop, two min work end shake...,why is this?


Reply:

If the compressor started and ran normally for two minutes, then stopped after shaking, I would suspect an over-pressure condition on the "high-pressure" side of the system. That can be caused by a blockage in the high pressure refrigerant piping or a stuck or frozen TEV - thermostatic expansion valve.

If I am correct that we are speaking Croatian:

Ako je kompresor započeo i trčao normalno dvije minute, a zatim je zaustavljen nakon tresenja, pretpostavljam da postoji pretjerani pritisak na "visokotlačnoj" strani sustava. To može biti uzrokovano začepljenjem u visokotlačnom cjevovodu rashladnog sredstva ili zaporenim ili zamrznutim TEV - termostatskim ekspanzionim ventilom.

 

On 2017-06-06 by asif - A/C compressor going on and off - is that a problem?

Compressor is going on and off

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

Asif

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 2017-05-06 by Mark - Ran the A/C with the cover on - is that OK?

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

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

Mark:

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 2016-06-22 by Anonymous - will a mini split work on both 60Hz and 50 Hz power?

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

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)

Check the manual and data tag. Often yes.

On 2016-05-08 by Peg - chipped reed valve cannot br repaired or replaced, so I require a whole new condenser

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 2016-05-08 by (mod) - sealed HVAC compressor motor is not repairable - it gets replaced

Peg,

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 2015-06-10 by Donna - Blue gummy substance used to patch refrigerant leak!

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 2015-06-10 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?

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

Reply:

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

Reply:

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 ARTICLE INDEX 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

Reply:

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

Reply:

JT our link at the ARTICLE INDEX 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

Reply:

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

Is it normal for there to be water coming out of the base of my compressor. (June 30, 2014) Anonymous

Reply:

Anon

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

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? (July 13, 2014) Anonymous 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? (Aug 2, 2014) Lou said:

Reply:

Lou

Check for a bad start relay.

Then see AIR CONDITIONER WON'T START

 

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

My AC is not cooling well don't know the problem with that.( Aug 14, 2014) Andre Matthew 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? (Aug 21, 2014) Wayne said:

Reply:

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

 

On 2013-01-18 by JR - Building owner doesn't want A/C compressors installed anywhere that they can be seen

DEAR SIR
I am an architect with limited technical knowledge of the mechanics of A/Cs but based on past experience I have noted that compressors are normally located externally to provide air circulation around them or else they'll pack up.

On one of the projects one of my colleague is currently involved with is where the building owner has specifically stated that he does not want anything including compressors or satellite dishes installed externally where they are visible. the mechanical engineer has instructed the sub-contractor to install these in a stair well.

My opinion is that this is not the correct location as the stair-well will heat up due to discharge from the compressors - which means we'd need to provide mechanical extract! but more importantly due to lack of fresh air the compressors will within a short time pack up and the A/Cs will not function.

The mech. engineer who disagrees with these observations! Please advise if I am incorrect in my observations and what are the remedies.

Please also note contractually we've done the paperwork in informing the mech. engineer that the instructions are incorrect and any malfunction of the system as a result will be his responsibility - so that has been taken care of but what I'd like to know is whether we can go around this problem by introducing ducts or substituting outdoor compressors with indoor units which are more cost effective

Reply by (mod)

In many buildings it's possible to install the compressor/condenser unit on the rooftop where it's not visible - but be sure to review noise control and noise issues for building occupants too.

Avoid fencing in the condenser units and avoid locating them where they can't be readily inspected or serviced. Otherwise the future maintenance and repair costs may be quite high and may be a source of new complaints.

On 2012-11-28 by David - Defrost cycle not working on outside condenser

My outside condensing unit has been missing the defrost cycle recently. Now, it will go into defrost cycle but will not return back to normal operation.

On 2012-11-28 by (mod) -

David,
That sounds like a bad defrost cycle relay switch or a bad control board.

On 2012-10-07 by Jim Lennox heat pump without a defrost cycle: stuck contactor.

I have a very old Lenox heat pump system. The "contractor" said it is 40 years old.

He mentions it needs a new Defrost Control Board (problem is the condenser fan always runs). I went snooping around the unit and could not find a board.

It appears to be a direct 220V connection too condenser unit; capacitors and simple contactor.

I found the contactor to be stuck.

I freed it up and all seems fine. I will replace contactor. Is it possible that this old lennox heat pump does not have a defrost control board or should I keep looking? Can it be in the air handler?? Thanks.

On 2012-10-08 by (mod) -

Jim
Not every unit uses a defrost cycle. If we had the model and serial number we might be able to looknup the unit specs.

Ask your service tech to replace the bad contactor and you may be good to go.

Thank you to our readers for their generous comments

On 2015-08-17 by princely

hi,
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 peppyetas@gmail.com thanks alot

On 2015-08-17 by (mod)

Princely

You can read our content copy and use policy in the comment just below.

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On 2015-04-13 by ANIL KUMAR

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

On 2012-07-03 by good

it's very useful to me,thank you.

On 2012-06-21 by sibte, shah

Thanks so much for bringing this excellent , comprehensive and easy to understand article. God bless you

...

...

 

Continue reading at COMPRESSOR / CONDENSER REPAIR or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR HANDLER / BLOWER UNITS - separate article series: blower unit or indoor components of heat pump & air conditioning systems
• COMPRESSOR / CONDENSER REPAIR - home
• COMPRESSOR / CONDENSER DIAGNOSTICS
• COMPRESSOR FAILURE DIAGNOSIS - Initial, simple diagnostic checks of the air conditioning compressor are also described
• DIAGNOSTIC GUIDE A/C or HEAT PUMP - suggestions for diagnosing compressor or condenser fan and coil problems that can mean intermittent or totally lost cooling capacity of your system.
• DUCT SYSTEM DESIGN SIZE & DEFECTS - separate article series

Suggested citation for this web page

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

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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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