Photograph of client using tissue to look for air conditioning air flow A/C & Heat Pump Repair FAQs-2
Diagnose Trouble w/ Air Conditioners & Heat Pumps

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Air Conditioning Troubleshooting & Diagnosis FAQs (list of frequently asked questions about air conditioners)

These questions & answers about fixing problems with air conditioners & heat pumps were posted originally on the air conditioning & heat pump home page.

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.

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Air Conditioning Systems & Equipment FAQs-2

These questions & answers about diagnosing trouble with air conditioners and head pumps were originally posted at AIR CONDITIONING & HEAT PUMP SYSTEMS

A good place to look for diagnostic procedures is DIAGNOSTIC GUIDES A/C / HEAT PUMP.

Also see this series of A/C & Heat Pump Diagnostic FAQs sorted by major topic area are given at AIR CONDITIONING & HEAT PUMP SYSTEM FAQs LIST

On 2017-07-27 (mod) said: no air flow and icy coil in new AC system from Sears

Sounds like an ice-blocked coil, perhaps from low refrigerant, improper charge or a refrigerant leak or an improperly-set thermostatic expansion valve . Call your service company for repair and let me know what you're told. Read more by using the search box above to find our article on COOLING COIL ICE BLOCKAGE.

On 2017-07-27 by Vin

I bought a new AC system from Sears bout no air flowing and ice formed on com pressure and copper tubing on Atic coil?

On 2017-07-26 by Robin Macera

I have what I believe to be a 1965 International Oil Burner Company heating and cooling unit. Heat quit working this past winter and cooling system comes on but isn't cooling.

On 2017-07-18 by Eric

The question i have is the condensate line for my ran directly into my shower where it is coming out of a p.v.c.pipe about ten to twelve inches off the floor of my walk -in shower is this a proper disposal location i notice that the front of my shower is always slimy and discolored and i have been having problems with my feet peeling that i never had before.thank you for any help you can provide in this question

On 2017-07-13 by (mod) Goodman hp 410 suction 200 lbs head 300 suction line slightly cool comp noisey

Seems like rather low pressure on the high side; is refrigerant lost or is the compressor not working?

On 2017-07-13 by mike

Goodman hp 410 suction 200 lbs head 300 suction line slightly cool comp noisey

On 2017-07-09 by (mod)


If the outside (compressor/condenser) fan never shuts off AND your thermostat is continuing to call for cooling and the compressor is running, then the condition is normal and should be OK.

If your thermostat is set to above room temperature, so that it stops calling for cooling, and still the outside unit or its fan never shuts off (say for hours) then a control, relay, or wiring is damaged and needs repair. In that case I'd turn off the system.

About your "prompt reply" demand, please try to find patience: we have over 200 million readers in 50 countries, so sometimes it's a bit difficult to give an immediate answer to every question. Apologies, we'll continue to try to be as responsive as possible. In a life-threatening or other dire emergency readers are also welcome to try contacting the editors directly using our page top or bottom CONTACT link.

On 2017-07-09 by Susan

Will it hurt if my outside unit fan won't shut off? Inside unit is working fine. Do I need to shut it all off until repair man comes in two days?

On 2017-07-05 by (mod) When I turn on my A.C. my heat comes on the furnace


First let's be sure that all of your thermostat switches are properly set. For example be sure the thermostat is switched to cooling mode.

Then if when you lower the temperature on your thermostat the heat runs instead of the air conditioning, then commom causes include

The thermostat is defective

the thermostat wiring is shorted, or it is miswired.

A control board or relay for the air conditioning system could be defective

On 2017-07-05 by Rechel

When I turn on my A.C. my heat comes on the furnace and all any suggestions?

On 2017-06-27 by Robert

Morning Dan,

So I got new condensor fan engine but this upgrade has four (plus ground) wires so the store which sold me it said I need additional capacitor.
I have absolutely no clue how to instal it, but after looking on the internet it seems that heaving two capacitors is not a great idea.
Is there something that could help me?
Thank you!

On 2017-06-26 by Duane Smith

Thanks for getting back to me. I know I have a confusing problem and do agree that we are not going to spend a lot on this 10 year old R22 system.

On 2017-06-26 by (mod) 10 year old 3 ton heat pump in Arizona not cooling adequately


Climate change and very hot temperatures in AZ indeed are showing up in many areas from cancelled air flights to failures in older or marginal air conditioning systems.

You offer a good and also frustrating example of a shotgun approach to HVAC system repairs.

I am reluctant, with even less information than they had, to second guess the service tech's.

I would call the repair company, speak with the service manager, explain that you are getting rather inconsistent diagnosis and repair advice, then ask for help from their most experienced senior repair tech.

In my opinion I would be reluctant to order a very costly repair on a now obsolete R22 based system.

On 2017-06-26 by Duane Smith

I don't know if you can help me. I have a 10 year old 3 ton heat pump in Arizona.

Last spring, before the hot weather came, we had the spring checkup done and the tech came off the roof and said we needed a new capacitor and fan motor to the tune of $900.

We told him to go ahead and a month later when it got time to run the AC, it would not work. The company sent out another tech and he said the capacitor was bad and exchanged it.

The unit then ran fine until we got the record heat of 118 a few days ago and the unit quit putting out cool air and the inside temps rose 5 degrees or more until evening when the unit started cooling.

We called the company again and the tech came and said we needed a new metering valve to the tune of $2500. He took the bulb sensor off the suction line and said that would make the unit let max Freon through all the time and it would work until we decided to have the valve replaced or get a new unit.

After that, we got a second opinion and this tech said removing the bulb sensor would not make any difference and he put it back in place.

He said the compressor amps seemed low when it was running and with the high ambient temperature, it should be running about max amps.

The compressor was getting very hot and that is why it was shutting down. He said it indicates the compressor is wearing out and not operating efficiently anymore. We are setting the thermostat to 75 to cool the house down from 5 PM until noon the next day, which lets the compressor rest during the highest temps of the day and then back to 80 at noon until 5 PM.

That has been working well and the temperature inside will pretty much hold until 5 when we turn it back to 75.

I know this may not be enough information for you to give me any advice but maybe you can possibly tell me which tech is on the right track. I think the first one was just trying to make a big sale because of the high price of replacing the metering valve. By the way, this is an R-22 unit.

Thanks, Smitty

On 2017-06-22 by (mod) enclosed the compressor/condenser of a walk-in refrigerator

I would check with the equipment manufacturer, but it seems likely to meet up the duct system with you describe is going to be undersized and we'll both reduce the effectiveness of the cooling system and shorten it's life

On 2017-06-22 by Richard U

I have a walk in refrigerator with a condenser compressor unit on the top, the ceiling was cut out to accommodate the condenser compressor placing it in the attic. The attic has now been renovated into living space and the heat from the condenser compressor on a warm day is unbearable.

So I enclosed the condenser compressor and ran a 10'x6" insulated duct from a shroud over the intake end of the condenser coil to the exterior to supply fresh air, I also ran a 16'x6" duct from the top of the enclosure to the exterior for exhausting the heat.

There is a fan behind the condenser coil that pulls air thru the condenser and blows on the compressor only for the length of time the refrigerator calls for cooling.

The shroud is not a tight fit over the front of the condenser about a 1" gap around the edges. I thank that I need a 6"duct booster fan on the intake duct to ensure adequate air flow and direction over the condenser coil to be controlled by a temperature sensor with contacts to control the booster fans on off time and to turn it on if residual heat builds up in the enclosure, also in the winter "Northern Wisconsin" to prevent it from getting to cold.

I don't want to reduce the efficiency by allowing the equipment enclosure to get to cold in winter or to hot in summer and create a damaging environment. I have not found information on the temperature range necessary to accomplish this.
I could use some advice on this situation,
Thank You

On 2017-06-16 15:18:10.942664 by Robert


I have changed the capacitor, but it did not fix the situation. Now I guess it is time to change the fan motor.

Before I do this could you please look into the video. I would like to get your go ahead before I embark on the motor swapping.
Thank you very much

On 2017-06-13 by Anonymous

Dan, thank you. we will look itno your advice. My husband said that it's more like a whistling sound.

On 2017-06-13 by (mod)


I don't quite understand the situation but I think you're hearing a duct noise that you didn't hear during the last cooling season. I'd inspect the full run of the duct system for crushed, collapsed or damaged ductwork.

Start at the air handler and be sure that the air filter is in place and undamaged. (We don't want to draw an air filter into the blower as that could cause a fire)

On 2017-06-13 by Rose

my home central air conditioning system, turned on after a long winter, now makes a sound from the vents as if the vents are closed and the air is trying to push out. the vents are all open. it is a whooshing sound. thank you.

On 2017-06-11 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 2017-06-11 by Anonymous

Thank you , I will do what you suggested.

Yes. I am sure compressor works (because it cools), I tried the AC Unit today and it was cooling for 20 minutes.
Since fan works fine for first 150-20 minutes I dont think it is blade or obstruction.

I am lucky because I have two floor house so I have another unit that cool upstairs, and I am using this one currently.

I will keep you posted after I change the start up capacitor..

Again, thank you!


On 2017-06-07 by (mod)


Sorry I missed it, please send me the video link by email found at our page bottom contact link.

Once an air conditioning system has shut down in most systems the pressure equalizes across the high and low sides.

If you're sure it's the fan not the compressor,

1. leave the equipment off to avoid further damage and unsafe conditions

2. Look for a loose fan blade on the shaft, an obstruction hitting the fan

3. Look for or just replace the fan motor start-run capacitor - search InspectAPedia for MOTOR START CAPACITOR for details.

On 2017-06-05 by Robert

Outside unit starts fine. After few minutes of work fan start making terrible noise, fan slows, speed up again ,and then completely stops. Condenser still works.
What would you make out of it? Thank you!

On 2017-06-04 by Mike

Split unit is just blowing hot air

On 2017-06-02 by satyamthetrue

1. Is it possible‚Äč for TEV to remain open for few minutes after units are shut down.

2. It's been more than 10 days since i encountered the problem and still there is no problem with the cooling.

If possible check my video.

On 2017-06-01 by (mod)


Because the thermostatic expansion valve on an air conditioning or heat pump system opens and closes in Cycles, it is not quite correct to assume that bubbles in the system will be heard continuously.

On 2017-06-01 by satyamthetrue

If it were a leakage the sound would come continuously but it is not so.Sound comes at certain interval,continues for around 2 to 3 min then stops and if units are turned off during that sound is live then it(sound)continues for few min but if turned off when no sound then everything happens in a normal way.

You would understand it in a better way by watching the video..Link already provided.

On 2017-06-01 by (mod)

re-posting without link - for security


It's possible that you are hearing gas bubbles in the refrigerant line - an indicator that there is a leak in the system.

On 2017-05-13 by (mod)

With the warning that I'm speculating beyond my expertise comma I'm considering your thoughts that the thermostat is defective.

It's generally easy enough to rule out both the thermostat and the thermostat wires as being a problem Source. Simply go to the other end of the thermostat wires, recognizing that for call for heat or call for cooling the thermostat is basically operating as an on-off switch.

So you want to be able to remove the thermostat wires and connect the two thermostat terminals for heating or Cooling.

Since you're not getting Cooling if you jump the cooling terminals I would expect the compressor condenser to run outside as a heat pump in cooling mode as long as the outdoor temperature is not too low.

On 2017-05-13 by Jim Brooks

I don't think the contactor is bad as it operates when I request heat. Just not when cooling is selected.
Do you know how the furnace and heat pump are cotrolled for cooling.

I guess operating the fan control turns the furnace blower on and whether or not the heat output is activated determines whether the furnace make heat or not.
My suspicion is the thermostat is bad given the fact from what I understand the thermistor/outside air temp sensor controls whether the heat pump comes on.

It's weird that the cool indicator is flashing indicating the thermostat is calling for cooling but neither the heat pump nor the furnace fan come on.
This is why I think it's the thermostat.

I bought a honeywell control but it does not have a sensor input.

On 2017-05-13 by (mod)

Jim I can but guess from the position of great distance and not much information, but to me this sounds like a bad control board or contactor.

On 2017-05-13 by Jim Brooks

I have a carrier heat pump/aux heat system . Recently it has stopped cooling.
It will heat and the pump comes on.

When cooling is selected at thermostat, I hear a click in the thermostat and the revering valve is operated outside
The internal fan does not come on and the heat pump does not start.
If I operate the contacter on the heat pump, the heat pump starts.

The system has an outside air temp sensor that connects to the thermostat.
Previously, the thermostat reported an OAT sensor fault.
I checked at the sensor and get about 3.7V with ambient about 10C.

I also measures the sensor resistance when disconnected. About 15K and going down when you hold it.
I measures the voltage at the sensor pin from the thermostat with sensor disconnected and read +5V.
Any thoughts suggestions?

On 2017-05-01 by Michael Riley

I have a Fedders A/C unit on my coop roof and an air handler in the apt. Lately when the A/c comes on there is a loud clanging noise about 10 secs after that in the refrigerant line that comes into the apt that lasts about 5 secs. The unit cools fine. Should I be concerned?

On 2017-04-28 by (mod)

We're in heat mode, right? Are you running in backup heat? If so the compressor/condenser would probably stop.

When no air is delivered then the air handler or its controls are not working properly in that I'd not expect it to shut off before the thermostat set temperature is reached UNLESS the air handler's heat exchanger in backup mode is overheating.

On 2017-04-28 by steve

i have a carrier heat/ac unit o o ntop of my house and the heater works fine, but it shuts off before the temperature is reached and I can hear the heat pump still working , but, no air is coming out or heat ..,

i usally pull the fuse on the unit and this fixes it temporarily, could it be the ignighter that or a photo scenser thats not cleaned off.
need a professnal opinion thank you steve in redding ca

On 2017-04-27 by Brian

@Mike, It sounds like the contactor has the contacts stuck closed. This is a common problem.

On 2017-04-26 by (mod)


Check out the diagnostic and repair advice at FAN WONT STOP - LIMIT SWITCH -

it could be a bad fan control or even just shorted thermostat wires

On 2017-04-26 by Mike

The fan on my AC unit won't cut off. The blower fan cuts on and off as you would expect with the thermostat, and it is cooling the house fine.

When I looked at the unit yesterday, the refrigerant line and the compressor were covered in ice. I shut everything off and let it melt off, but when I turned it back on today, the unit can still won't turn off. I can't find my information online on this particular problem, so I don't even know wheee to look.

On 2017-04-26 by (mod) Trane single packaged 3 ton heat pump fan randomly cycles on and off


I would look for

- a loose wire at the thermostat or between thermostat and the air handler

- a failing fan control or switch

- a fan whose wiring, control relay, or start/run capacitor is failing

BUt the fact that the fan behaves badly only in OFF suggests the first of these: a loose or shorting wire, or perhaps a bad thermostat

On 2017-04-26 by Krjune

Any ideas why fan behaves this way. Have a Trane single packaged 3 ton heat pump that when the heat/cool switch set to off, the fan randomly cycles on and off.

If the switch is set to either heat or cool, the fan turns on and off with the cycles properly. Fan switch is set to Auto.

On 2017-04-12 by (mod) fence around my outdoor HVAC air unit


I certainly doubt that the ONLY air circulation path at your compressor/condenser unit is "from the top" - air has to move IN, across the condensing coil and OUT.

Blocking either inlet or outlet will increase cooling costs and reduce the life of the compressor/condenser unit.

On 2017-04-09 by BJ

I am replacing the fence around my outdoor HVAC air unit. It gets circulation from the top. I want to build the fence with a 12" clearance on just one side, more clearance on the other sides. Is this an acceptable installation for zip 34231, Sarasota County, Florida?

On 2017-03-11 by (mod)

I took a look at (and downloaded to examine) your photo - I see what looks like light corrosion on copper refrigerant tubing and rust on the galvanized metal frame that holds the cooling coil.

It would be no surprise that there would be more corrosion lower on the coil - as in the photo - as more condensate will tend to accumulate lower on any sloped coil;

These diagnostic questions occur to me, and others might be raised by other HVAC service techs

1. most important, and not easily seen, is there corrosion, damage, or blocking to the cooling fins in the cooling coil body: depending on the severity, including more severe than what I see in your photo, that may mean end of life of the cooling coil and on a 20 year old system, possible system replacement as I noted earlier. With a light and inspection mirror it may be possible to get a look at the coil condition through the small triangular openings at the ends of the A-coil frame.

2. if during system operation we can see ice or frost forming on the coil sufficient to block air flow then I suspect low refrigerant, and thus a refrigerant leak that needs attention; again depending on leak severity and where it is occurring, that could also precipitate a more costly air handler and possibly compressor/condenser unit replacement.

3. Stains on the cleaning instructions label on the condensate collection tray suggest that there may have been tray overflow in the past; A service tech would check that the condensate drain is not blocked and that condensate leaks have not damaged the heat exchanger of the furnace presumed to be below the cooling coil in the photo - as serious rust or damage to a heat exchanger may make the furnace unsafe.

The replacement question arises because while it makes sense to do inexpensive repairs to keep using equipment as long as feasible, at some point we don't want to start throwing much good money after bad.

(with your permission I'll find a place to post the image and this discussion, so you might use our CONTACT link to contact me by email).

On 2017-03-11 by (mod) corrosion around the ends of the evaporator coils


info said:
It was on the copper tubing. There is a photo at this link

On 2017-03-10 by (mod)

Interesting question, Jonathan, perhaps other readers will comment. Was the corrosion on fins or on the tubing? Was the tubing copper or aluminum?

Indeed a badly corroded coil may precipitate a complete AHU system replacement since replacing the coil alone on a 20 y.0. sysetm that is using an obsolete refrigerant may not make economic sense. It'd make sense to issue that near-end-of-life warning.

On 2017-03-10 by Jonathan Quigley

I recently performed an inspection of a forced air furnace with heat pump. I noted corrosion around the ends of the evaporator coils, most notably near where the condensate is collected. Is there a common diagnosis for this condition? The unit is about 20 years old

On 2017-01-28 by Bill

Daryl it sounds like you have a stuck relay.

On 2017-01-28 by Bill heat strip relays short out and it blew the Air handler board

Heat pump question. I had heat strip relays short out and it blew the Air handler board. I replaced the board and relays and now the heat pump works and blows warm air but I get no 24v at the heat strip relays. (When I checked I was getting 2.5 volts). What could be the problem keeping the board from turning on the heat strips?

On 2017-01-24 by Daryl

Any ideas where to START LOOKING ?

2 weeks ago it was 70% outside, front door was open and windows too, my furnace came on (set at 35%) and heat would not shut off.

On 2017-01-24 by Daryl

my electrical furnace of a 1999 Fleetwood double wide will not shut off by thermostat, only by shutting off main circuit breaker. Replaced new thermostat and still will not go off. thermostat is not hooked up and just turned breaker back on and furnace came on and still running, is it a short in wiring ? can't have furnace running all the time !!

On 2017-01-21 by (mod)

Sorry Anonymous, and Sorry Mukesh Punia,

our security won't permit posting of advertising links in comments, even though certainly we know that people in South Delhi need electrical and air conditioning repairs. You can, however contribute technical content, critique, reviews of the material you find at and that enables us to cite and link to technical contributors/reviewers. - Editor - See more at:

On 2017-01-18 by Bobby

My frigitare ac/heater compressure keeps running when I power down the unit . To get it to stop is to use the breaker switch on the head of the cord! Any ideas?

On 2016-12-2 by (mod) remote control reads 17 degrees celsius while the indoor unit is reading 24 degree celsius

Perhaps the remote is in a different location than the wall unit.

On 2016-12-19 by Solomon

an air conditioner remote control reads 17 degrees celsius while the indoor unit is reading 24 degree celsius instead of the 17 degree celsius set on the remote. What could be the cause?


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