A/C or Heat Pump Fan Condenser Unit Fan diagnostic questions & answers - FAQs No. 3.

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

This article series 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.

More HVAC Compressor/Condenser Fan Diagnostic FAQs

These questions and answers were posted originally

at FAN, COMPRESSOR / CONDENSER UNIT - be sure to see the repair advice at that page.

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.

Reader question: can you use your A/C as a fresh air vent fan?

all I want to know is how to get new air into a room without the AC running. Can the fan be used for this?

when the AC is off and only the fan is running, is the fan just moving air around in the room or is it replacing the air in the room? 2018-09-20 by Carolyn Reese

Mod reply:

Carolyn

Sorry to be vague but ... as Mark Cramer says: It Depends.

If you are running a window AC unit AND if the window unit has a control that will admit outdoor air, then yes you can run the unit in fan mode and blow outdoor air into the home.

If you are running central air conditioning AND if your central AC system includes an outdoor air source you can do the same. But that would be uncommon in residential air conditioning systems.

So in my third case, sorry, but no. If you have a typical home central AC system and you just run the blower fan alone, it will circulate air and thus may make the building a bit more even in temperature but it won't be bringing in fresh outside air.

What I do, when the weather is suitable, is open a window and stick a box fan in the window, blowing IN.

In a prior home that had a whole house exhaust fan we had a better solution: when it cooled off outside we'd open windows downstairs, then turn on the whole house exhaust fan that drew outside air in the windows, up through the house, and out through the attic and roof exhaust.

Reader question: a motor can be bad but check out OK on the bench when it is not running

Is it possible for a condenser fan motor to be bad even if

1)the windings ohm out correctly and

2) there are no shorts of the leads/windings to the case?

Motor shaft turns freely, no wobble, slight in and out play on the shaft, maybe 1/4" to 3/8".

I was out of town when the AC quit. Tech told my wife the capacitor was bad ( it does check out bad) as well as the fan motor. She made him leave the old parts, so I checked them. Comments? 2018-09-05 by MPG

Mod reply:

MP

Regrettably yes, a motor can be bad but check out OK on the bench when it is not running. That's because when the motor gets up to speed a wire can open due to the centrifugal force exerted on the rotor -the rotating component in the motor.

If a motor hums and won't start a common inexpensive thing techs try is to just replace the starting capacitor or to install a hard-start capacitor. Search InspectApedia.com for HARD START CAPACITOR to see details.

Reader question: fan spins slow

I replace condenser motor and capacitor fan spins slow what could be causing this. 2018-08-17 by valleyworld25

Mod reply:

VW

some possibilities include a loose connection, a bad capacitor or wrong value capacitor, low voltage, or failing motor.

less likely a loose fan blade

Reader question: Motor fan is running backwards

Older Bryant A/C. The condenser fan finally failed. Found a replacement Motor and Capacitor from NA and installed. Motor fan is running backwards (pulling air in top, thru the coils and out the sides.

Motor was equipped with stacons on the orange and yellow wires and you are supposed to disconnect them and connect both orange to yellow to reverse rotation. Reversed wires, still rotates the same direction.

The capacitor is a 3 wire (one each end, one in middle). Installed the cap in same orientation. Tried swapping the power leads (black/white), motor wouldnt turn (just a brief pulse, sounded like a 3 phase motor being single phased), switched them back.

The Cap is an exact replacement, but should I try putting the old one in? Motor-Emerson K55HXSSM-7146, Cap is a Cera-Mite 305CIS 5uf... Thanks 2018-08-08 by JJ Smith

Mod reply:

When a fan runs backwards it's mis-wired (or has been struck by lightning); It sounds as if you are perfectly on top of the wiring directions to reverse fan direction.

If that's not working but the fan ran fine in the wrong direction I don't suspect the capacitor I suspect a wiring error such as an inadvertent short or internal damage in the motor. Sure it won't hurt to try the old cap.

Watch out: as you may know, making a mistake can shock you or kill you.

Reader question: My AC is only blowing air

My AC is only blowing air. When I checked the condenser the fan is blowing downward instead of blowing up and out! 2018-07-20 by Joan Nering

Mod reply:

There are some units designed to move air from the top down and out through two or three sides across the condensing coil.

But if your fan has actually reversed-direction, as is possible with some motors, it could have suffered a power surge or lightning strike. See

ELECTRIC MOTOR RUN DIRECTION https://inspectapedia.com/electric/Electric_Motor_Direction.php

Reader question: fan stopped working, but the compressor was still running

Just replaced fan motor, replaced contact capacitor, new air filter. AC was running fine for a week, then the fan stopped working, but the compressor was still running. Now when I turn my air on, the fan runs for 15 seconds and shuts off with the compressor still running. Any ideas? 2018-06-13 by Anonymous

Mod reply:

Sounds like a bad fan relay. Check for a connection that's opening up when the motor heats up.

Reader question: What happens if compressor is intentionally kept Off for a few minutes

What happens if compressor is intentionally kept Off for a few minutes and the condenser fan is running for that time? Is it detrimental to the system? 2018-05-24 by Jyoten

Mod reply:

No not at all, however cycling air compressor off and then back on to quickly can damage the compressor motor by forcing it to try to start against the high head pressure.

Reader question: Condensing unit fan squeals

Condensing unit fan squeals before it's at full speed then runs great. 2018-05-17 by Sax

Mod reply:

Check for

- a bad fan motor bearing

- a bad fan start capacitor

Reader question: What happens if condenser fan stop running

What would happen if one of my condenser fan's stop running? 2018-02-17 by Will

Mod reply:

The condenser unit cannot function and should shut down on over pressure or temperature.

Reader question: outside compressor rotation fault and high compressor amps

Nordyne unit with IQ drive keeps throwing an “outside compressor rotation fault “ when on heat mode. Does this once or twice a day any thoughts? Also saw a “ high compressor amps” pop up. 2017-12-13 by Mike

Mod reply:

High amps usually means that a compressor motor is unable to start. If it's a heat pump and it's supposed to be able to run, resuming that you're in a cold-weather area and therefore are running the heat pump in heating mode, Maybe the compressor cannot start because the crankcase heater has failed.

Follow up:

Yes I’m in Pa and it only happens during heat season. It started near the end of winter last year and it cooled all summer with no issues. As soon as we switched back to heat mode it started again.

Mod reply:

Check first for a bad heater on the compressor

Reader question: outside fan will not come on and the unit begins to freeze up

I have a Coleman heat pump and have replaced the capacitor. The inside furnace will run and heat but the outside fan will not come on and the unit begins to freeze up, what could this be? 2017-12-05 by Angela

Mod reply:

I would look for a bad fan relay

Reader question: condenser fan motor and compressor stopped working

I have the Worry Free insurance on my outside AC Unit. It's an old unit! It's an Armstrong unit that is 20 years old at least. The condenser fan motor stopped working. The compressor stopped working also.

Worry Free came and replaced the condenser. Still nothing. Ordered a new fan motor and replaced it. Still nothing except now the compressor works! Fan not working but compressor is . . . could the wires be crossed? Could Worry Free have installed the new parts wrong? 2017-10-23 by Frank

Mod reply:

Frank,

You ask a completely fair question but not one I can diagnose from just this e-text. Certainly if the condenser unit fan isn't working do not run the compressor motor as overheating can damage the system.

When you say they replaced the condenser - I'm not sure what was replaced - not the compressor motor, right?

If the fan isn't working typically it's one of the problems discussed on this page above: a bad control or relay, even a loose wire or connection, or a bad fan motor or bad fan start/run cap.

Those are things a tech would typically have checked. You might ask the service manager to send out a senior technician in hopes they can stop losing money by repeated repair calls.

Keep me posted - what you find will doubtless help other readers.

Follow up:

1st . . . nothing worked. Only a hum like it was trying to turn on, but fan and compressor didn't work. Next the condenser was replaced. (silver, about 4 inches long, snaps in to place). Fan and compressor still didn't work.

Then another tech returned with the new fan motor. He installed that. Fan still not working, but compressor did fire up. I know you can't give me a complete diagnosis, just wanted to give you the facts. Thanks!!! I'll keep you posted.

Reader question: ac has not put out cool air since the fan blade was replaced

My husband replaced the fan blade on our ac unit because it was loose and making a lot of noise. Our ac has not put out cool air since he did this. Is it possible he caused other problems? 2017-09-26 by Wanda

Mod reply:

Wanda

IF there is NO air output then I suspect there is a problem at the fan or blower unit. But if there is air output of air that is not cool enough, working on the fan itself shouldn't cause that problem - unless by accident hubby left a wire disconnected at a control relay or board.

Reader question: Can a condensor fan running backwards cause evap coil to freeze?

Can a condensor fan running backwards cause evap coil to freeze up? 2017-08-08 by Anonymous

Mod reply:

Anon:

If a backwards running fan means that the proper CFM of air flow across a coil does not occur, in a CONDENSER in cooling mode (air conditioning mode if it's a heat pump) then the condenser will be too hot, the high pressure gas will not adequately cool to liquid form, but none of that would cause icing of the outdoor coil.

An indoor evaporator coil will freeze up if air flow is reduced or cut off for any reason: backwards fan or dirt or dirty filter.

Reader question: Compressor contacts disengage and fan still runs

Compressor contacts disengage and fan still runs, disconnected thermostat and still runs, wont shut off unless pull disconnect. 2017-07-09 by Ron

Mod reply:

Ron

Which fan - outside compressor/condenser?
Anyway, look for

- shorted thermostat wires - disconnect them at the blower or compressor unit end

- a bad fan relay

Reader question: CarrierAC keeps running, shutting off, restarting

I have a new carrier 2 1/2 ton 83,000 but heat pump. When the ac is running and it reaches the temp on the thermostat, the cooling shuts off, then immediately restarts and runs for a few minutes, then stops again. What causes this? 2017-07-04 by Lynn

Mod reply:

Good question. Im not sure of the cause but suspect

A bad thermostat

Loose or corroded wires or connection

A bad a.c. control or relay

Reader question: Is it common to see compressor ground out after replacing condenser fan?

Question-Is it common to see compressor ground out after replacing condenser fan?

Carrier AC-Fan was making screeching sounds periodically, and also only operating at 70%, so had it replaced. Condenser also replaced. When tech installed new fan, it was confirmed by error code with Carrier, that compressor grounded out.

Tech said that with the high amperage coming off new fan, compressor was used to the amps coming off old fan, and it grounded out because of this. I don't know a lot about AC units, and compressors, but could my contractor have caused the compressor to ground out? 2017-06-09 by Ron

Mod reply:

I don't think so, Ron, those sound like separate problems. However if there was an "event" like a lightning strike that might damage both the fan motor and the compressor motor.

Yes a mistake during work on any electrical equipment might accidentally touch a live electrical component to ground, causing damage or worse, a shock. But of course we can't know by a simple e-text what your contractor was doing nor if there was any possibility at all that she caused the trouble you describe.

Reader question: fan on AC unit will not spin

My fan on AC unit will not spin tried by hand won't even move a bit I tried with both hands. 2017-06-07 by Jim

Mod reply:

Jim,

With electrical power off, if you are unable to rotate the fan at the compressor condenser unit, then it sounds to me as if the motor bearing or motor itself has seized and the motor will need to be replaced.

Reader question: Is it safe to run AC unit, even for short periods, until capacitor replaced?

I know my dual capacitor needs to be replaced. Is it safe to run AC unit, even for short periods, until I can get it done? 2017-05-30 by Thornton

Mod reply:

Thornton,

I don't know for sure. If the system starts and runs, you can run it. If the compressor or fan motor hums and doesn't start then you need to leave it shut OFF as that humming is drawing current that could damage the motor or its controls.

Reader question: condenser fan runs intermittently

I have a brand new payne outdoor ac unit. The condenser fan runs intermittently. Runs for about 3 seconds then off for about 10 seconds. And does that continuously. Is that normal? Any info would be appreciated. 2017-05-22 by Geoff

Mod reply:

Geoff

That sounds like a bad control board or relay, or perhaps a loose connection. I'd think that if the problem were a motor overheating the motor would stay off longer than 10 seconds.

Follow up:

The salesperson assured me that this was normal to keep the pressure high? I don't think its how it's supposed to be though?

Mod reply:

Geoff

I don't pretend I know more than a full time HVAC expert technician, but gee: it really sounds abnormal me for a compressor to continuously short cycle on and off every 10 seconds and I'd expect that cycling to ultimately damage a control, relay, or the compresor itself. It's enough of a problem that we have an article on it

SHORT CYCLING AC COMPRESSOR at https://inspectapedia.com/aircond/Air_Conditioner_Short_Cycling.php

I worry when encountering what sounds like baloney that someone is just brushing us off, figuring that when the system dies they'll sell us a new one.

Call the service department, ask to speak not to a sales rep but to an experienced service manager. Politely ask that they send a more experienced tech to look at the problem.

Keep me posted as what you're told will help others.

Follow up:

Thanks for the link and your comments. I called the customer contact # at payne and they do not have anyone that answers technical support questions. They said talk to the retailer. That go me nowhere.

This is brand new unit and was fired up for the 1st time and was intermittent fan. The condenser is running fine and it seems to cool the house, issue is with the fan. I found some info saying depending on the outdoor temperature, the fan will cycle on and off, more so on when its a hot day outside and less when its cooler out.

They said it possibly has a "head pressure control" allowing it to run in low temps. Someone also suggested a faulty defrost sensor.

I only ran the unit for 15 minutes , but wanted to do more research on the intermittent fan before running longer. I will run it for longer tomorrow, Its supposed to be fairly warm outside so will see if the fans runs in longer cycles.

Mod reply:

Geoff

Wonderful. What a perfect short-term-bottom-line grab the money and run business strategy that you describe about 8 Payne Heating & Cooling S 7310 W. Morris St. S Indianapolis, IN 46231. Putting the customer last is a good way to wipe out your business.

The company's customer contact number (888) 417-2963 is probably what you called. What you report is disappointing for a company that's been around since 1914. At the company's website https://www.payne.com I also did not find more technical support information.

A sample Payne owner's manual http://www.utcccs-cdn.com/hvac/docs/1009/Public/0E/OG-PAYACR410-01.pdf offers 2 pages of general operating instructions and no troubleshooting advice.

What's left is to call the service manager at your local HVAC repair company and ask for a more-experienced service technician. But first read the SHORT CYCLING AC COMPRESSOR article so you're familiar with the terms and common causes of the trouble.

To be more clear: is it only the fan motor that's short cycling or is the compressor itself cycling on and off rapidly?

I'd also check again for a loose wire or other electrical component like a relay or board connector.

Follow up:

Yes great customer service! I was surprised no technical help. It is just the fan on the outdoor unit thats cycling 3 seconds on, 8 - 10 seconds off.

The compressor was running steady during the cycling of the fan. Let you know what i come up with, Thanks.

Mod reply:

Got it now, Geoff.

Let’s look again at the case where the outdoor compressor/condenser fan is cycling on and off at short intervals - in seconds:

The list of possible causes of an intermittent HVAC compressor/condenser fan operation when the compressor motor itself runs normally includes at least:

- a bad fan motor start/run capacitor

- usually easy to find and swap out for a new one so often the service tech will start by just replacing this part.

Often a tech will replace both the start/run capacitor AND the fan or condenser+fan relay since that can save the cost of a second service call.

These are not expensive parts. You can also find more about start/run capacitors at InspectApedia - CAPACITORS for HARD STARTING MOTORS

Watch out: also that a remaining charge in a capacitor can shock you even if power is OFF - an expert will ground the capacitor terminals to dissipate any remaining charge. The capacitor specifications are printed on the device.

- a failing fan motor that's overheating - when the power is turned off after the system is on for a while see if the motor feels very hot - some motors include an internal thermal reset - this is of course a more expensive part to swap in so try the capacitor first.

- a bad fan control relay in the compressor/condenser unit. If the fan cycling were running at odd times/intervals I'd suspect a bad connection or loose wire but if it's regular cycling on and off more likely it's a control problem (or overheating)

- less common: a fan motor winding that opens when the motor gets up to full speed

- other electric motor defects cited at the motor diagnostic article series

see ELECTRIC MOTOR DIAGNOSTIC GUIDE and in that article series

we also have an article on ELECTRIC MOTOR RESET BUTTON

WATCH OUT: there are very serious hazards when fooling around with the compressor/condenser unit including death by electric shock or having fingers chopped off in a spinning fan. If you’re not trained/qualified to do this repair work, it’s best to hire a trained service technician. In any event, be sure power is off before getting closer into inspection of the equipment.

Reader question: speed of the air that takes away the heat from the refrigerant in the condenser

what would be the speed of the air that takes away the heat from the refrigerant in the condenser? 2017-05-10 by Sagar Lokare

Mod reply:

Air speed can vary considerably in a residential low pressure HVAC duct depending on system design. The speed ranges from about 175 cubic feet per minute to 5900 cubic feet per minute. Most likely you'll be in the low end of that range.

...

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

Or see these

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Suggested citation for this web page

FAN, COMPRESSOR / CONDENSER FAQs 3 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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