Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked. HVAC Compressor / Condenser Fan FAQs

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A/C or Heat Pump Fan Condenser Unit Fan diagnostic questions & answers - FAQs 2:

More questions & answers help diagnose problems with the air conditioner or heat pump condenser unit fan

This series article discusses the diagnosis and repair of problems with the outdoor compressor / condenser fan and fan motor, including fans that wont' run, fans that run at slow speed, and fans that won't stop running.

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More HVAC Compressor/Condenser Fan Diagnostic FAQs

Air conditioning compressors overgrown with shrubs (C) Daniel Friedman

Avoid confusion between the indoor blower fan and the outdoor condenser fan: the compressor / condenser fan is in the outdoor unit and is used to cool the outdoor condensing coil. If you are troubleshooting the indoor air handler that delivers cooled or heated air through the duct system and supply registers, see BLOWER FAN OPERATION & TESTING - home.

Recently-posted questions & answers about the air conditioner or heat pump compressor/condenser unit fan:

On 2017-04-14 22:57:10.566120 by (mod) re: why the technician intalled an "emergency" capacitor

I suspect that the technician installed a "hard start" capacitor because the standard cap was having trouble starting the motor.

On 2017-04-14 16:03:57.305894 by eddieo

I just would like to know the reason somebody instead of just change the bad capacitor. He installed an emergency capacitor?

On 2017-04-11 23:07:19.864719 by Anonymous

condenser making hum noise, fan not working

On 2016-12-14 02:30:51.867149 by Jaron

Hello. I have a Rheem RBHP-24J18S air handler that has me pulling my hair out. One night I noticed only the blower was running with no heat coming out of the vents. The next day I climbed in the attic to check things out but didn't notice anything out of the ordinary. After some research I noticed the most common problems were sequencers, control board, and thermostats. I actually had a new thermostat and control board for a spare so I changed them along with the sequencers.

Then set the heat on auto to start the cycle and the blower came on and a few seconds later the air began blowing out the vents harder and warm. Everything seemed to be worked fine but a few minutes later the air flow slowed down and it was blowing cool air. I went back to checking things and found the defrost control switch was failed open so I changed it along with the watt restrictor switch. Now I don't get any heat at all just seems to be the blower blowing cool air.

I checked both sides the transformer and getting 24V and 240V and getting 24V going to the control board. I also noticed after turning on the AC that after the cooling cycle is over and the compressor shuts off the blower continues to run for a minute or the heater should do after the heating cycle is complete. Any help solving this would be GREATLY appreciated!

On 2016-10-14 12:00:01.474735 by Anonymous

We recently purchased a Condo in Florida with the Condenser Unit located in a small Utility Closet on the Lanai. The unit has a 24" wide x 14" high sheet metal box and 4Ft X 24" round exhaust elbow mounted on top of the unit leading to the vent on the building wall. The noise from this 6 year old unit was unbearable.

A/C Company said everyone here has the same complaint and that we have to live with it. Wrong answer. I installed a Compressor Blanket, cut a 10" hole in the side of the Sheet Meal Box and installed a 10" Duct that vents to the outside. What a difference. Exhaust air flow is no longer restricted and we can sit outside and have a conversation.

On 2016-09-30 00:04:04.999639 by (mod)


If the replacement fan motor meets the operating specs of the original one it should be OK. Moving the actual fan blades inside the condenser unit might indeed change the airflow pattern enough to be worth thinking about.

For example a typical condenser fan draws outside air IN through the condensing coil around the sides of the unit and blows the heated air UP and OUT at the top of the unit. If changing the fan assembly caused some of the exiting air to blow against the upper sides of the condensing coils you'd be reducing their effectiveness.

If the condenser unit is less efficient than it was before it might have to work harder and longer. But I think your tech will look elsewhere if the house is too warm.

On 2016-09-29 09:04:10.307435 by Anonymous

fan motor in outside unit went bad and installer used different fan motor than came on unit when new now the fan is lower in unit 2 or so inches and system seams to not cool house as easy any thoughts on this one end of season now

On 2016-08-16 18:38:50.005578 by (mod)

Well absolutely is a pretty strong word from a nervous technician.

A wiring error or missing the real problem could either be at fault.

Often when a compressor is hard to start it's because it's seizing and at end of life - could have been damaged by a variety of problems. The tech sticks on a hard-start cap because that's dirt cheap to try and might keep the old boy cooling a bit longer. But it's no surprise if the compressor itself is shot and now needs replacement. It was probably shot before the cap was installed.

A sharp tech might have confirmed that the compressor is really shot by at least measuring the current draw at the motor.

On 2016-08-16 17:03:29.761040 by Anonymous

We recently had our "Start capacitor" replaced on a 9 year old Trane HVAC. 3 days later, unit stopped cooling and technican says "compressor is shorted to the ground". When asked if the start capacitor replacment could have created any issue with the compressor shortage, he said "absolutely not".

That seems inconsistent... If the starter capacitor is a "energy booster" to the compressor, how could it be completely unrelated? So my question is, could/is it possible for a new start capacitor install create an "energy event' which would cause the compressor to short out? The tech said there was no way they could be related technically, Just need an HVAC genius to provide their insight. I would appreciate it. I'm looking at 2400 to replace compressor or 7K for new unit.

On 2016-06-26 13:15:06.140782 by (mod)

Simply elevating a compressor/condenser up a bit would not in itself cause it to fail to operate.
Look for disturbed electrical wiring, a broken wire, a switch that was left OFF, or a thermostat wire or control wire that was broken or not re-connected.

On 2016-06-26 12:54:15.918307 by Thedevotifamily

We lifted our compressor fan and placed blocks underneath so we could pour a concrete slab and now it won't kick on but the indoor unit is working. What do I look for?

On 2016-06-24 17:33:23.890492 by (mod)

If the replacement cap didn't give more than 8 hours of running I suspect that the motor is failing; keep in mind that some motor problems such as a winding that opens when the motor is spinning, can be hard to find. Search for ELECTRIC MOTOR TEST to see some diagnostics.

On 2016-06-24 12:37:01.315352 by jesterdan

Condenser fan wasn't running. Read out the motor, Appeared good, replaced the run capacitor, came back to life for 8 hours and the fan stopped again. Any ideas?

On 2016-06-20 10:38:47.510242 by (mod)

sounds like a bad relay, control, or shorted wires.

On 2016-06-20 10:35:55.094367 by Anonymous

The blower fan on my central unit runs intermittently even with thermostat off ... The unit runs fine but this motor runs intermitently even if unit is off at thermostat... Changed thermostat and capacitor .. No help...

On 2016-06-17 02:53:35.521558 by (mod)

Nice going, Jay.

On 2016-06-17 02:16:17.718233 by Jay

Thanks again for the help Daniel, That is exactly what I did Today and after cleaning and lubricating the old motor it still cut out after a while just took longer. Went to the supply house and got a new motor. I test ran it out of the unit and no more cycling. Must have had a shorted or open turn which caused the old motor to overheat or open up. End of story, I am ready for hot weather, maybe I get another 10 Years out of it!

On 2016-06-16 14:40:57.051014 by (mod)

Jay often we'll test the motor out of the unit by wiring it directly; even before doing that, if the motor shaft doesn't turn easily that's an indicator of a mechanical problem; electrical motor problems can be subtle as a winding may only open when a motor spins. Search InspectApedia for ELECTRIC MOTOR TESTING to see more suggestions if you like. DO keep me posted.


On 2016-06-15 22:31:07.693676 by Jay

Thanks for the help Danjoefriedman, Must be the motor itself, Think I'll just replace both and see if that fixes it.

On 2016-06-15 22:12:58.113172 by Jay

Cap seems to be OK too, On high scale of the simpson (100000ohm) get full deflection then infinitive . When I reverse the leads it is the same , no short to case. Don't see much on the 10K scale.

On 2016-06-15 21:57:25.017112 by (mod)

On 2016-06-15 21:52:49.112639 by Jay

connections look OK nothing loose & full voltage all the time, how can I check the start /run Capacitor?

On 2016-06-15 21:46:59.911917 by (mod)

Check for a loose connection or a bad start/run capacitor.

On 2016-06-15 21:15:39.874786 by Jay

Hi I have an old Williams AC unit Has been working fine for about 15-20 Years. When I started the AC this Year, the outside unit Fan and compressor started up OK then after 20-30 seconds the fan shut off while compressor kept running. Then the fan started again for some seconds and quit it just kept cycling. It is a 220 fan motor and the voltage stayed constant on my Simpson. What can I do?

On 2016-04-01 15:10:20.705719 by (mod)

I can only guess, anon that someone thought the motor needed protection from weather - normally the outdoor A/C compressor/condenser is left exposed to the elements. DO NOT TURN ON this motor while it's covered in plastic. Overheating or jamming up a motor or fan can cause a fire.

On 2016-04-01 14:36:30.122698 by Anonymous

there is a black plastic bag on the motor of my outdoor AC unit. Why

On 2016-03-06 22:19:58.499430 by (mod)


I'm not sure what's moving up and down - that is, if the shaft wiggles from side to side when moved against the motor bearing I suggest the bearing has failed. But end play described as a movement of the motor shaft in and out - say by pushing or pulling on the end of the shaft so that you are pushing it into our pulling it out of the motor, as opposed to side to side against its bearings - that may be OK.

On 2016-03-06 03:13:12.744343 by Kevin

My condenser fan motor shaft has up and down play but the amp draw is good. Is the fan motor still bad?

On 2016-02-06 16:00:36.577074 by (mod)

Yes if you have a heat pump and if outdoor temperature is above the heat pump's lowest operating range.

On 2016-02-06 by Dave

When I turn my heat on my condenser comes on, Is this normal ?

On 2016-01-24 by (mod)

I would turn on backup heat if it's not on automatically, then call or repair.

On 2016-01-23 by Marie

Hi, I have a honeywell heat pump and the outside fan doesn't come on the inside heat is running, should i turn the inside thermostat to emergency heat

On 2015-12-08 by (mod)


The problem may be a start-run capacitor on the fan motor, or a bad control or relay.

Search for STARTING CAPACITOR to read details.

On 2015-12-07 22:57:05.150250 by keith H

when I turn my a/c unit on the outside fan starts spinning and about 1 min later it slows down and like 10 seconds later it cuts back on running the way it should. it did it off and on. the air inside never gets cool enough to cool the place down.

On 2015-11-17 02:25:55.225367 by (mod)


Erratic bad behaviour is particularly hard to diagnose as it tends to vanish when the service tech shows up. I'd be looking for a loose wire or a bad control board or relay.

When it wont' run, that's the time for the service tech to start doing some probing with her electrical test tools.

On 2015-11-16 17:17:49.780508 by Diane

My AC/Heat unit runs erratically. It runs perfectly on heat/or cool then it quits working. When it quits working the thermostats controls-heat,cool and even fan or auto fan will not work. This may last for hours or days ,then it will start working again. I have had a highly recommended service company come out. First they said it was wired wrong, when they left it was working, but within an hour it quit working. When they came back they said it was the thermostat and put in a new thermostat and a third time with another thermostat. It worked for about 15 days and then started working erratically again. Now they want to replace the main board. Any suggestions? thanks

On 2017-03-15 00:36:37.553202 by (mod)

Readers: if you don't see the information you need, just post a comment or question and we'll reply asap.


Normally on a heat pump in winter in heating mode, indeed ice can form on the outdoor coil and will require defrosting, handled automatically - especially when outdoor temperatures are close to freezing.

You should observe the following if the system is working normally:

- inside the heat will stop, or will switch to backup heat mode; most units have a signal or indicator light indicating defrost cycle mode

- outside the fan stops and the compressor is running.

But the requirement to go through a defrost cycle depends on outdoor temperature and humidity. So your system may not need to be defrosting as often as you think. Articles I've read on this suggest that typically you won't see a defrost cycle more often than about every half hour or 35 minutes.

If the inside indicators are defrost mode then yes I think the fan should stop - there could be a control board or fan relay control problem or an outdoor temperature sensor failure.

Watch out: as a general note for other readers, don't turn off the system in the middle of a defrost cycle - let it complete the defrost cycle or you may damage the equipment when it's re-started.

Temperzone, a New Zealand company I admire, has a nice article on the defrost cycle - at


(Nov 3, 2016) joon said:
good information, thank you admin, anyway some information share for you, i think Tower fans have one major favorable position when contrasted with other home fans: they are totally compact. Most are extremely lightweight and permit you to rapidly lift them up to move them. Long strings compliment this element with the goal that you can move the fan into position and feel good on even the hottest of days.

On 2017-02-05 15:23:23.043828 by Stewart

I replaced my condenser fan motor this summer. Now that winter is here I noticed my unit is not defrosting as it should and ices up. Couple things I noted. The fan is running in the right direction. The fan does shutdown when the condenser unit shuts down, The fan continues to run during the defrost cycle and I am not sure if this is correct. Should the fan be off on the defrost cycle? What would be the cause to it continuing to run?

On 2016-10-31 21:06:32.532990 by (mod)

Or could be a bad control board or relay. I'd start by confirming that there is electrical power to the unit.

Watch out: you could be killed by electric shock. If you're not trained to fool around with the compressor/condenser unit and its wiring I'd recommend hiring a service tech.

On 2016-10-31 20:21:13.279310 by Ken C.

Have a florida heat pump and compressor doesn't turn on...replaced capacitor...still doesn't turn on...checked all circuit breakers, etc..did find a frayed wire ( black ) that plugs into the contactor..cut the bad part out and replaced the spade connection...still doesn't work...thermo. is set for 70 degrees..temp. inside is 78 ...seems like there is a reset or fuse somewhere that is noise or humming etc...Not sure where to go from here...

On 2016-09-14 18:44:57.504933 by (mod)

Good diagnostic - especially if nobody gets fried.

That suggests a bad fan control, relay, or control/relay wiring.

On 2016-09-14 17:41:54.067492 by deena edwards

I straight wired it in it runs good

On 2016-09-14 17:35:19.950707 by (mod)


One can but guess that as the control board is new and guessing that the fan relay is on the control board the trouble is elsewhere. I expect your service tech will check voltage, loose wiring, fan motor start/run cap, fan bearings.

On 2016-09-14 17:20:35.206886 by deena edwards

i bought a new coleman control board for my heat pump in the fan is only running for 3 min than cut off

On 2016-08-30 04:02:11.060454 by Anonymous

condenser fan is very noisy i have replaced the fan and motor and i have leveled the unit but condenser fan is still very noisy

On 2016-07-26 22:33:56.831704 by (mod)


Ethel's answer is immediately below your question.

With millions of readers, sometimes I must say, with apology, that not every question gets an immediate answer. But we continue to try our best, and hope that other generous readers who have expertise in the appropriate area will also chime in from time to time with an authoritative, informed, expert reply to reader questions.

On 2016-07-26 13:16:39.471642 by Anonymous

I see peoples problems, where is the answers?

On 2016-07-17 15:43:52.333809 by (mod)

Ethel, probably the problem is one of those discussed in the article above - you're on the right page.

OF course start by confirming that the outside unit has electrical power and your thermostat is calling for cooling.
Your service tech will check for:
- a bad fan start/run relay
- a bad fan start/run capacitor
- a failed fan motor

On 2016-07-17 14:15:24.060053 by Ethel

My fan won't work on the outside unit, what could be causing this?

On 2016-07-04 16:49:38.371360 by (mod)

OF course: just turn off power to the unit while you are waiting for repair.

On 2016-07-04 05:21:13.270721 by Nancy Pierce

This unit isnt working to cool the house, but it is putting heat into the house. You can hear the fan by the blower running constantly. Is there a switch to shut it off or can i disconnect wires. Help im getting sick and dust is also being blown in.

On 2016-07-04 05:14:33.082093 by Nancy Pierce

The blower fan inside the furnace keeps running and its putting heat into the house when its 80degress out.

On 2016-06-17 22:26:50.625774 by TODD Cohen

My central heat and air stopped working I had to look at it he said it could be capacitor do I change the capacitor the same Wilson on fan but when I put it on AC it blows breaker could I have a bad capacitor or is there another problem

On 2016-06-08 05:44:17.228357 by hank .wallace

Can I safely run a 55+5 uf MFD fan start capacitor in the place of a 30+5 uf MFD both at 370 VAC or will the 55 damage the compressor?

On 2016-06-06 11:29:55.319996 by Anonymous

husband put screen over top of fan to prevent sticks/leaves from falling into heat pump unit. will this cause damage to unit?

On 2016-04-30 14:37:07.126777 by chris

heat pump condenser fan will run for a few minutes and shuts off,the fan is red hot but won't operate. in the cooling mode the heat pump blower motor operates and blows air but the condenser fun won't run.

On 2016-04-24 13:06:13.931355 by Anonymous

My heatpump unit outside is not working right. When the temp gets above 80 the blower that moves air though the house stops working. If I turn off the beaker for about an hour and then turn it on the unit runs normal I've had tech out several times and can't fix this. This is a Trane system about 2 years o!d. What can I try?

On 2016-03-03 18:20:22.808382 by (mod)

The fan motor is now probably shot - or its capacitor is shot. Leave it switched off until that's reparied. Meanwhile you're on backup heat.

On 2016-03-01 14:35:18.913705 by cathy

The fan outside our unit has quit running a month before I heard a little hum for a few seconds every once in awhile now that breaker is tripped we put it back on and it tripped the breaker again so now the breaker is off the heat works fine but the blade is not turning outside could you help me with that please

On 2015-11-06 17:33:12.037313 by (mod)

It sounds as if a switch remains off or is not functioning.

I found this diagnostic article by searching InspectAPedia for "air conditioner won't start"

On 2015-11-06 00:21:06.341221 by Anonymous

Outside unit fan will not come on after my husband cleaned the outside unit coils. He pulled the outside switch to cut the power but he also said that the compressor and fan were off before he pulled the outside switch. Help, he's an operator not an a/c man.

On 2015-09-10 06:29:06.707779 by Nikhil Prasad

My AIR COOLER (NOT A/C) runs for sometime and then its fan and water pump shuts off but the auto swing keeps running.

On 2015-08-20 10:55:32.450253 by Sridhar

3 months old General AC, out door unit fan running slowly(70%) with little humming. In the first 2 months it worked perfectly.
Can any one say the reason?? Thanks

On 2015-08-16 17:48:13.405230 by (mod)

Your HVAC service tech will perhaps check current draw and look for signs of a failing compressor motor.

that's provided of course the capacitors were properly selected and wired

On 2015-08-15 01:02:24.006362 by Malcolm

I changed the capacitors in two units and in the addict it worked for a while and then they one went out and the fan stop spinning in the unit. I got a hard start for the other and it worked for a while then the fan stopped spinning in it as well. Neither prior to the capacitors were removing hot air. What should I do next?

On 2015-06-12 11:29:33.583360 by (mod)

If a motor is overheating that ought to be discoverable by some basic electrical tests of current draw;

On 2015-06-10 22:17:20.312530 by anon

Hello, here is my problem that hasn't been fixed even after a few technician visits.
The a/c unit turns on and after a few minutes the compressor turns on blowing out cold air. However the compressor shuts off after ~10 minutes, and normal/hot air blows out. It doesn't ( or rarely) starts back on after 30 minutes.
My guess are -
Faulty thermostat
Overheating motors (which ones exactly?)
High voltage (we get higher than normal voltage in our area..the stabilizer shows a voltage of 250+..however when the voltage is in the range of 200-240, it runs fine for even up to 2 hours..coincidence or some problem with the unit?)
Any help will be appreciated, thanks.

On 2015-06-09 19:08:36.658500 by (mod)

Look for a bad start-run capacitor.

On 2015-06-09 18:18:56.608770 by Lill

Outdoors condenser unit starts only after manually spinning the blades a few times. Once it is off for more than an hour the same process must be repeated to make it start again
Does the fan motor need replacing??


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

Or see FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs - questions & answers posted originally at FAN, COMPRESSOR / CONDENSER UNIT - home

Or see CAPACITORS for HARD STARTING MOTORS for capacitors that may get a fan motor spinning again.

Or see COMPRESSOR / CONDENSER DIAGNOSTIC FAQs for questions about the compressor / condenser compressor motor or condensing unit itself.

Or see these

HVAC Compressor / Condensing Unit Diagnostic Articles

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