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Photograph of an old burned-out air conditioning compressor unit Air Conditioning / Heat Pump Compressor Diagnostic FAQs #3
Recent Outdoor AC Unit Diagnostic Q&A

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HVAC compressor / condenser diagnostic questions & answers or FAQs:

This air conditioning repair article provides diagnostic questions & answers for the outdoor compressor / condenser unit used on air conditioners & heat pumps. These questions and answers help diagnose an compressor motor that is not working, compressor noises, condensing coil performance, or for heat pumps, outdoor coil icing.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Diagnostic Questions & Answers for HVAC Compressors & Condensers & Fans

AC Compressor © D Friedman at InspectApedia.com These questions and answers about troubleshooting and fixing air conditioner or heat pump compressor/condenser units were posted originally at COMPRESSOR / CONDENSER DIAGNOSTICS - be sure to check out the diagnostic suggestions on that page.

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On 2018-10-27 by (mod) - what to do if heat won't shut off

Gloria

When your central heating won't turn off regardless of what you do at the thermostat, that's probably not a heat pump or compressor/condenser unit problem.

Instead, see the diagnostic steps at HEAT WON'T TURN OFF

On 2018-10-27 by Gloria

My central heat continuously run and does not shut off when it reach the temperature set on thermostat what could this be it

On 2018-07-20 by (mod) - repair technicians "best guess" is not a bad approach

Cora

No. The tech is sometimes making a "best guess" diagnosis of what's wrong and replaces the most-suspect or obviously bad part.

I sympathize with your irritation at having to "pay twice".

But I've been on both sides of this transaction.

At a mechanical system service call I might point out to a customer:

Me: "Look at this valve - it's corroded and leaky, and sometime soon it's going to leave you without heat - then you'll have the extra cost of an emergency service call. It should be replaced now."

Customer: "Stop trying to build up your bill by adding on stuff I don't need. Just do what I asked you to do - clean and tune the system. Don't replace anything else."

A heating or air condtioning service tech who, under the aegis of being responsible and professional, runs into responses like that from customers eventually gives up and does just what's obviously and un-arguably needed, avoiding getting hassled for "replacing extra parts that probably were not needed".

So you can see it can be difficult to navigate.

Bottom line: hire service people you trust. Then it's up to you to discuss the repair with the tech the time. You have the option of asking if there are other parts that are suspect and that could be replaced now, saving the cost of a second service call. Once you've given the technician an understanding of your view point, she will be able to accomodate.

On 2018-07-20 by Corasoma

During 90 degree weather our AC was blowing warm air and AC repairman replaced Capacitor; next day the AC stopped working again and he replaced the Contactor

-charged $125 for service both days and said it was just bad luck that these two parts broke down at different times - should he have replaced both the first time?

On 2017-12-04 by (mod) - you need an onsite Goodman HVAC service tech

It seems likely that we need an on-site service technician to help sort this problem out. From what you have said so far I am guessing that there is a bad control or relay in your heating system

- that is you're running a heat pump in heating mode. As you probably understand when it's quite cold out the heating pump cannot keep up and backup heat switches in. But it sounds to me as if the temperature in the room is never reaching the thermostat set temperature.

It's also possible that your backup heating system is not working correctly. Some backup heat that is electric uses multiple heaters in series and it may be that not all of those are working.

On 2017-12-04 by Phil

When my Goodman unit is in heating mode the outside unit and the air handler turn on. The air coming through the ducts is cool. The thermostat is set to 72 degrees the room temp. Is 69 degrees ,the aux. heat turns on bringing the inside temp. To 71 degrees it drops out and the outside unit still runs with cool air coming through the ducts dropping the inside temp and turning on the aux heat again.

It just repeats the cycle never turning off, any help would be appreciated.

On 2017-12-01 18:01:16.387120 by (mod) -

Lois

My sympathy.
What you ask is a legal question , probably depending on your lease.

Perhaps a written signed statement from the service company would be helpful, but I expect the service co is not going to want to get in between you and your landlord

On 2017-11-30 05:56:02.883161 by Lois martin

I've lived in my apartment four years and my AC went out. On other occasions it would come on and only blow warm air. My landlord sent a repairman three different times.

The replaced the coil. Then my AC just stopped working. Again a repairman was sent and he said it needed to be replaced because all the wires burned up. I asked the repair man if it was my fault he said no. I asked him even if the filter is dirty he said no. Now almost two months after its replaced he is now trying to make me pay for some of the replacement charges even tho the repairman said it wasn't my fault. Can he do that?

On 2017-09-04 20:56:35.503361 by Cynthia Ridaught

Handle comes on and blows cool air not very strong but it is some. Outside unit is not coming on though. What could this be.

On 2017-07-12 14:47:52.191065 by (mod) -

Thank you for the helpful feedback, that will benefit other readers as well

On 2017-07-11 03:02:14.224325 by Jesse

@danjoefriedman
So the tech came out he replaced a capacitor a relay and for some weird reason there was a panel that wasn't screwed down in the intake that was opening every once in awhile like a 3-foot gap letting in hot air once he did all those things the AC hasn't blown fuses and has been running fine

On 2017-07-07 01:07:46.981577 by (mod) -

When a motor is blowing a fuse or tripping a circuit breaker I suspect that there is a failing bearing or other motor component.

On 2017-07-06 22:41:03.625421 by Jesse

I have a guy coming to look at it tomorrow. So you think it could be in an internal shut off even though the unit runs fine it satisfies itself with the temperature, turns itself off then when it turns itself back on (not every time) it'll run hot for the 20 minutes and then start cooling?
I will definitely let you know what the guy tells me tomorrow.
Thank you for the reply

On 2017-07-06 04:59:32.433833 by Jesse

I Have an older Lennox 5 ton unit. Sometimes when the unit starts it will blow hot air for 20 minutes then it would start cooling but not every time. On some occasions it would blow the fuse.

On 2017-06-11 23:56:32.564727 by (mod) -

This sounds as if a motor is overheating and tripping an internal thermal overload.

That would explain why after a cool down period the system will run again. I'd ask for a service call - of course the problem could be elsewhere (such as an overpressure and shut down by a safety control) so let me know what you're told.

On 2017-06-11 23:01:40.062803 by Phil

Hi, My AC comes on normally and runs between 15 and 30 mins. Then my compressor makes a weird noise and everything loses power without tripping the breaker. The display goes off and the compressor will not turn on. After about an hour everything comes back on and the cycle continues. Please help me.

On 2017-04-21 23:22:59.723220 by (mod) -

Sounds like a bad control or relay, but really I am reluctant to pretend to be smarter than the on-site technician.

When you call for cooling at the thermostat, does the outdoor compressor motor start and run or not? That's the question the tech surely considered.

On 2017-04-18 13:10:54.909779 by jude

Central A/C unit blows cold one minute and hot the next. This has been going on for years. It's good for months at a time and then starts again. Service man checked outside, upstairs and thermostat and could find nothing wrong.

He suggested a hard start kit. Would that solve this problem?

On 2017-04-07 00:36:59.549725 by (mod) -

OK so for completeness I'll add that it's not a complete surprise for two pieces of equipment made at the same factory on the same date to fail close together in time. I've seen that failure pattern in other situations, even the electrical spark plug points contact spring in my old Norton motorcycle.

One spring broke (of course far from home and on a trip) - we were clever enough to buy replacement points sets for both left and right cylinders and lucky enough to find a place to buy them without getting arrested - but that's another story.

We took of down the highway, having replaced the right hand points set. In less than 50 miles the other set failed in the same way.

It's also imaginable that a power surge such as during a thunderstorm or from the electrical company or caused by human error working on equipment damages a capacitor, control board, relay, that in turn causes subsequent major parts failure.

EG a surge that damages a start cap can in turn mean the bad cap ultimately leads to motor failure.

If I wasn't clear earlier, a system will overheat when the fan isn't working. Overheat -> damage.

All of this is SPECULATION - your AC guys have surely seen more failures than I.

On 2017-04-07 by JH Our first sign something was wrong was the abrupt noise.

BTW, the tech told me this older unit did not have the safety control. The new unit they installed is a Goodman 14 SEER.

Both guys that installed the newer unit came out. They were baffled. One of the techs did his pressure or whatever test and showed me the needle not moving (exactly what I was shown when the other unit died).

Our first sign something was wrong was the abrupt noise. It's not been that hot here, so we couldn't judge if it was cooling or not.

The unit, however, on about 50% of the time, from when they gave it the OK on Saturday and it failed Monday night. Weird, not much pops up when you Google anything related to the fan motor causing this. FYI: A friend recommended these guys who has used them for 4 years.

On 2017-04-06 by (mod) - Fan motor failure causing compressor failure

JH
No I've not seen that as a common compressor failure cause, though it is possible indeed if it leads to a compressor overheat.

I think the reason we don't see that more-often is perhaps because compressors (at least many) contain safety controls that will shut the system down on over heating or on over-pressure. With the fan OFF the compressor is pushing high temperature gas out into the condensing coil but the coil isn't condensing it back to a liquid.

So we don't get liquid refrigerant back at the TEV (thermostatic expansion valve) so refrigerant won't be properly metered into the cooling coil in the indoor air handler - and we lose cooling.

That doesn't quite explain why you reported lost refrigerant. So the explanation leaves me a bit confused.

On 2017-04-06 by JH

One more question and I'll shut up. Fan motor failure causing compressor failure (as the tech said) doesn't seem to be a common problem (as web searches go). Just curious to get your thoughts. Thanks!

On 2017-04-06 by Anonymous

Sorry, itchy trigger finger. I meant to say the fan motor was replaced July '15. We live in Ft Worth where it gets hot!

Fan motor failure is what the tech said caused the compressor to die. This is a Lennox R-22 installed in '06 (same for the other we juThe fan motor in question was replaced in

On 2017-04-06 by (mod) - abrupt loud noise from the compressor

Your addition of the observation of an abrupt loud noise from the compressor does not sound to me like just a simple refrigerant loss problem. It sounds more like a bearing failure or motor failure. It's possible, however, that loss of refrigerant can also mean loss of lubrication which at least in some compressor designs could damage the motor bearings. I think these are good questions to ask the manufacturer of the unit.

On 2017-04-06 by JH

Thank you and sorry for the delayed reply. So is your speculation the only obvious cause?
Let me add to this in case it helps with a recap. I'll call the unit we just replaced "Unit 1" and the one that just went bad "Unit 2".

• Diagnosis of Unit 1 failure – 2 days before install: the tech showed me the difference between the lines running into the home.

• He pointed out that Unit 1 had oil and residue on it indicating it was leaking, etc. whatever the technical stuff is.

• He then pointed out that Unit 2 was dry and clean (I saw it with my own eyes).

• They checked Unit 2 the day they installed Unit 1, not before...and this is when they said it was good to go.

Lastly, and again, Unit 2 starting making the metal-on-metal sound just over 48 hours after they checked it. It seemed to work fine until then. THE NOISE WAS NOT GRADUAL, IT HAPPENED VERY ABRUPTLY AND LOUD. Thank you for your help!

On 2017-04-05 by (mod) -

JH

Ugh. I really really HATE to blame the technician - as they get blamed far too often for stuff they didn't do.

But in this case, and speculating, IF the other Lennox unit was working fine before it was examined, and IF shortly after it was examined it failed and the system was found to have lost its refrigerant, THEN perhaps the technician's "check" of that unit included hooking up a refrigerant pressure gauge to the refrigerant ports AND perhaps the test port valve, that should close and seal automagically when the gauge is disconnected, had some dirt that was pushed into the valve, leaving it partly open and leaking.

On 2017-04-05 12:33:56.699536 by JH

Two Questions: (1) Can A Bad Compressor Fan Motor Burn Out A Compressor? (2) Would replacing one compressor affect the other?

• I just had one of my compressors and its coil replaced. The technician checked my other (10 year old Lennox) compressor and said Freon levels looked good and it was running fine.

• Three days later we heard a really loud screeching, metal-on-metal-like sound and called the tech.

• Diagnosis: Fan motor failed burning out the compressor. Main symptoms: (a) warm air coming from fan; (b) no freon.
Thanks!

On 2016-06-14 14:52:01.976007 by (mod) -

Indeed, Christopher, as refrigerant systems include some oil, often the first sign we see of a small leak is an oily residue on refrigerant piping, below connections, or around other components (such as a compressor or expansion valve) that carry refrigerant.

It's best to find and fix the leak rather than just adding refrigerant.

On 2016-06-14 13:36:29.354086 by Christopher

This site is awesome! Thanks very much for helping this old man do basic troubleshooting on a/c unit! I highly recommend people read f.a.q. 1st, then follow steps as suggested.

On 2016-06-14 11:54:18.940898 by Christopher

I took the fan off of the top and peering down inside found the manifold piping shiny with a film of oil. I suspect it is time to call a service tech and have the tech do a leak test? I am assuming it must be a pinhole leak as the unit was running fine earlier in May and is only a few years old. Thank you so much for your help danjoefriedman!

On 2016-06-13 23:01:10.428490 by (mod) -

If the compressor motor and fan motor run I think the Pastor may be mistaken.

First take a look at LOST COOLING (search InspectApedia) for a list of simple diagnostic things to check, step by step.
That will take you to this article (or use this link)

https://inspectapedia.com/aircond/Air_Conditioner_Diagnosis.php

On 2016-06-13 20:46:42.032499 by Christopher

The central a/c unit at church is blowing warm air, both lines going to the outside unit are at outside temp, motor contactor was pulled-in and fan was running. Pastor thought we had a bad capacitor. Where should I proceed from here?

On 2016-04-09 21:08:38.584360 by (mod) -

First try resetting the equipment by turning the power off, waiting 5 minutes, and then turning it back on.

You can also eliminate the thermostat and it's wiring from the problem by disconnecting the two thermostat wires right at the heat pump.

Now if you jump over together the two thermostat terminals at the heat pump, that is the two terminals that should turn on the device, if it doesn't run the problem is there in a control board or relay.

On 2016-04-09 15:09:02.072604 by donno13

Question- My wife and I decided to put a programmable thermostat on out Trane XR12 heat pump. We got the wrong one, it was incompatable. I put the old thermostat back on, and the heat won't come on. As far as I can tell I didn't damage the old thermostat, and I'm sure everything is reconnected properly. Is there something I need to know to re-start the heat pump?
Thanks,
donno13@hotmail.com

On 2016-02-13 16:58:19.767794 by (mod) -

Sounds to me as if we haven't found the root problem. I can't see enough infomration from the e-text to have an opinion other than that an onsite service tech is needed. Sorry.

On 2016-02-13 15:50:59.627886 by terry

I have a Goodman heatpump package unit the compressor and condenser fan (topfan) do not run in heating mode or cooling mode I had a friend who does this walk me through some stuff and there was no power getting thru the defrost control board so I replaced it now power goes thru the board but no 24 volt to the contactor

On 2015-10-20 03:33:32.473479 by Anonymous

Sounds like a seizing motor. Time for a repair call

On 2015-10-20 02:31:20.390416 by Lee

I moved into my upstairs condo unit 11 years ago. I'm not sure how much older the heat pump is than that. The problem started last year. During the summer after working fine for weeks, instead of cycling back on it would vibrate the indoor unit quietly, crescendo loudly and then suddenly stop. A minute or two it would try it again.

Sometimes if I turned the thermostat down while it was doing this, the a/c would start and work fine for hours or days until it would do it again

. If that didn't work, I had to flip the furnace and a/c breakers for several hours before it would start correctly for a little while. In the winter, the same thing happens even after the compressor was changed and the capacitor and fan were said to be fine.

Last night, I turned on the heat and it ran ok until this morning, when it started the rumbling sound again instead of coming on.

I turned the thermostat up and the heat started up, but the rumbling sound continued in the background. I went to the breaker box and flipped the furnace breaker, which did nothing. Then I flipped the a/c breaker and it cut off.

This has been going on for a while and is very annoying. Not sure if it's related in anyway, but it is low on freon and was icing in the summer. Also, the insulation is cracked in spots and the pipes ice up as well when the a/c is on. Any help would be appreciated. Thanks!

On 2015-10-13 13:50:35.110368 by Judy corvino

The coil to heat the oil in mycompressoro my Trane ac burned out. Is it necessary to replace one tech said yes the other said no. I amconfusef

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

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

He talked me into a new trane xr13, 4 ton, r-410 condenser and a 5 ton evaporative coil for an extra $400. saying I'd get 10% more cooling capacity than the 4 ton coil. this was 5 weeks ago. three techs have been here since trying to figure out why the evaporative coil keeps icing up.

the best cooling we get with the thermostat set at 72 degrees is only 15 degrees cooler than it is outside.this is with the front panel off the furnace.

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

The HVAC guys tried to blame my ductwork as unable to handle the airflow, then inadequate air returns, then too small a hole (10x12) above the coil going to the plenum. all solutions of course would require a 2nd mortgage.

My response was . BULL. It's something they did wrong because before the compressor blew, if the outside temperature was 100 degrees, inside it was 78 degrees.(with the thermostat set at 72.

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

Reply:

Cooling coil icing can be due to an improper refrigerant charge, inadequate air flow across the cooling coil, or a problem with a refrigerant metering device (or something else we haven't thought-of).

Your HVAC guys might be right that your old duct system is not moving enough air across the coil, allowing it to ice up, but if that's the problem I'd ask them why they didn't think of that before selling you that extra big evaporative coil in the air handler.

In a good-working air conditioner or heat pump system the components need to be in balance: compressor/condenser, air handler/evaporator, and ductwork.

If we hold off on the blame game for a bit, let's see if you can increase the airflow across the coil.

Often I find on older cooling systems that the return air opening was too small or the connections from return register to the air handler small or cramped or twisty.

A very crude "test" that I do NOT RECOMMEND for more than a few minutes of test operation is to see if the coil ices up if someone leaves the air handler blower compartment door off - to maximize the return air opening.

Take a look under DUCT SYSTEM & DUCT DEFECTS for the article

: RETURN AIR REGISTERS & DUCTS,

and also take a look at COOLING COIL or EVAPORATOR COIL

and 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: compressor just runs for a few seconds, then cuts off; short cycling A/C compressor problems

My condenser starts for a few seconds then cuts off cycle continues - Anon.

my compressor fun has started to short cycle, it run for 2-3 min then shuts off for one second then restarts runs again then stops etc. with no funny sounds or noises - Don

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Reply:

It's not clear from your question where in the entire cooling system your unit's troubles begin, so I'd look at diagnostic tips that may explain your compressor/condenser short cycling are found

at LOST COOLING CAPACITY.

Certainly a compressor that is having trouble starting can be diagnosed

at HARD STARTING COMPRESSOR MOTORS, if you're sure the trouble is outside.

Question: ice on the refrigerant line, no cooling in the house

My line set going to outdoor unit has ice on it. Lost cooling in house. What is the problem and is there anything I can do to fix the issue - Pat

Reply: check the indoor air handler for an ice-blocked coil

A problem with a refrigerant metering device (thermostatic expansion valve, capillary tube, etc), or even a dirty air filter can lead to improper metering of refrigerant into the indoor cooling coil, leading to icing; but other causes of ice formation include an improper refrigerant charge or even something as simple as missing refrigerant line insulation.

But when you also lose cooling inside, I suspect an ice blocked coil.

See FROST BUILD-UP on AIR CONDITIONER COILS

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

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

Reply:

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

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

Blower fan running but reduced air flow (Dirty filter?) Air is not cold. System was on for a couple of hours when I noticed condenser fan.

It was not running. Turned system off, waited a while, turned system on. Condenser fan hummed but was not turning.

Used a BBQ fork (ok, not smart but I’ve never been accused of being too bright) to hit fan and it started. Still no cold air, ran for an hour, compressor fan motor and compressor VERY hot (Burned my fingers twice to confirm, that "not so bright thing again.”) Suggestions? - William 6/21/11

Reply:

William: when the outside compressor motor runs but the cooling fan does not, I suspect a bad start/run capacitor on the fan motor (if yours uses one) or a bad fan motor; sometimes it's a bad control board circuit.

If (with power turned off for safety) the fan spins freely if pushed, the motor is probably not frozen; in that case also see if there is a motor overload reset switch that can be pressed.

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

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

Reply:

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

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

Late last week, the fan on my outside unit began making a squealing sound and next morning the unit was blowing very warm air inside. I walked outside and found the

Fan had stopped but the motor seemed to still be running. I then shut the unit off and called a repair service to fix or replace the fan motor. Motor was replaced and seemed
to be working properly.

Now, after 5 days of use, the fan has again stopped and the unit
is once again blowing hot air.

Anyone have any suggestions? - Ronnie 7/3/11

Reply:

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

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

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

Reply:

Linda: you are describing the indoor air handler unit for your air conditioning (see the article link at the ARTICLE INDEX the bottom of this article titled BLOWER FAN OPERATION & TESTING]

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

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

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

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

Our fan is working on the inside, but the compressor unit will not turn on at all, so the air blowing is not cool. I've called multiple service techs, so far none can come out today (it is in the 90s!!),

one MIGHT be able to come out tomorrow and I am waiting on a call back from another.

Of course our house is on the market and we are supposed to have an open house tomorrow. Right now I have the whole system off at the thermostat, but keep hearing the inside system begin to start for about 5-10 seconds and then stop.

Any tips to check? We've thrown the breaker to the furnace and the compressor.

Our furnace is a dinosaur (but a strong one!!), the compressor unit is maybe 8 years old. - Laura 7/9/11

Reply:

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

Question: indoor fan runs but outdoor compressor is not spinning

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

Reply:

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

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

I investigated a noise coming from my compressor & found that the fan had fallen off and was lying at the bottom of the unit.

There was a slight burning smell, but the motor still appeared to be running. I turned off the unit...Do you think the fan just needs to be reattached or does the entire motor need to be replaced? - Janet C 7/11/11

Reply:

Janet:
Good going on a commonsense investigation and diagnosis of a serious problem.

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

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

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

Reply:

Monica,

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

Reply:

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

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

I have a very old Lennox compressor unit that died 2 days ago. WHen trying to determine what was wrong I turned on the unit from inside the house and when I went outside to inspect it the smell of burnt oil was in the air.

Then, when I looked at the condenser, the pipe looked like it was glowing red.

So, it's now time to change the unit. My question is would the pipe to my furnace and the A unit be contaminated with oil and other chemicals from the compressor?

Do I have to change the complete system, or can I simply replace the compressor unit? Thanks. - Pat 7/23/11

Reply:

Pat, in short, yes.

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

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

This drier is discussed in more detail at the article REFRIGERANT DRIERS & FILTERS (links at the ARTICLE INDEX the bottom of this article )

Question: trailer air conditioner not kicking in

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

Reply:

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

Question: My A/C unit kept blowing a fuse, now nothing runs

My Center A/C unit had a tuned up. I clean the evaporator, I put the blower down and put the new motor and clean the blades deeply, I have a clean filter, I clean the condenser deeply, and I bought a new thermostat. OK.

The unit star running normally and you fill the normal warm air in the fan (outside) But 3 to 5 minutes later the heat in the condenser air increased suddenly the condenser stop with noise, and I need to turn it off. what is this? Please give me a clue? - Anon 6/28/22

I have a pretty old Tappan unit, and when the power goes out, if the A/C is running it will blow the fuse, usually we just replace the fuse, and now nothing will run on the A/C unit. any ideas? - Shantel 6/20/11

Reply:

Shantel:

Often when an A/C unit keeps blowing the fuse it's a sign that the compressor is drawing high amps which means it's jamming which, I'm sorry to say, means it's at end of its life.

I'd have a service tech look at the unit; it might limp along for a while longer if s/he installs a hard-start capacitor kit. When "nothing runs" you may have meant that the fuse or breaker tripped enough times that you've lost power on that circuit.

Anonymous - from what you describe you need a service call from a trained HVAC tech.

Question: My hi line is cold, low line is warm and the condenser blows hot air

In my situation the high pressure line is colder than the low pressure line. The condensor coil blows mainly hot air, but the end closest to the compressor blows hotter air than the end furthest from the compressor line. Any suggestions? - Jim T. 7/13/11

Reply:

Mundo suggested: hey jim t check for restriction at the evaporator

Jim T:
Also, is your unit a heat pump or only an air conditioning system? - Editor. Let's be sure your system is in cooling mode.

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

Or see BURNED-OUT COMPRESSOR

Or see CAPACITORS for HARD STARTING MOTORS to try to kick start a reluctant compressor motor

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HVAC Compressor / Condensing Unit Diagnostic Articles

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COMPRESSOR / CONDENSER DIAGNOSTIC FAQs-3 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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

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