Photograph of attic air conditioning air handler, condensate drips on floor Air Handler Blower Unit Repair FAQs
Blower Assembly Diagnostic Q&A Set #3

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FAQs on repairing Indoor air handler or blower unit for A/C or heat pump or furnace systems, set #2:

More Q&A on AHU or air handler unit / blower unit troubleshooting and repairs.

This article series explains how to inspect & repair the indoor components of air conditioners and heat pumps: the air conditioning system indoor air handler units, blower units, or AHU's, (also called fan coil units) including the air conditioner blower fan, the indoor cooling coil or "evaporator coil", air conditioning system filters, and the causes, cures, and prevention of air handler leaks that lead to rust, damage, and mold contamination in the air conditioning system.

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Air Handler / Blower Unit Diagnostic FAQs - 3

Photograph of toxic mold growth on a squirrel cage air conditioner blower fan unit[Click to enlarge any image]

These questions & answers were posted originally at AIR HANDLER / BLOWER UNITS - home or at BLOWER FAN OPERATION & TESTING- home. Be sure to see the diagnostic and repair advice that begins in either of those articles.

The air handler page is the more-broad topic addressing all components of the air conditioner or heating furnace air handler while the blower fan page focuses on the fan itself and its direct controls.

On 2018-01-05 by (mod) - Could a blower fan coil that's burned out keep the heat and air conditioner from working


On 2018-01-04 by Jesse Hall

Could a blower fan coil that's burned out keep the heat and air conditioner from working

On 2017-12-22 by Tony

Our AC fan inside the unit is not running right. When the AC is kick on the coolant pumps in the unit but the inside fan is not running until 10 min. or sometimes longer. Sometimes it’s has ice buildup in the machine. Need help.

On 2017-11-21 05:00:26.931490 by (mod) -


A heating systems that requires a draft inducer fan should be wired such that if the draft inducer doesn't run the burner will never turn on. Because without the proper draft the system could be unsafe. If that's your situation then it sounds as if you need help from a heating service tech to find out why your draft inducer doesn't run.

On 2017-11-21 by Jerry

I have a Carrier single stage furnace that at start up the inducer motor doesn’t run but the fan blower does

On 2017-11-08 by lauramoh262

I have an older forced air belt drive oil furnace (not sure of age or mfg). The burner is working properly. The blower however does not come on when it should. If i give the pulley belt a little spin by hand the blower motor starts to run, but otherwise doesn't on its own. The belt isn't loose.

On 2017-10-26 by Randal

I have a XL13C model 4WCX3036A1000BA that sends a horrible chemical odor in to the house thru the vents when the coil cooling fan kicks off and the blower motor continues to run. Is the unit in defrost mode and how do I prevent the odor or stop the odor from coming in the house

On 2017-10-05 by Dixon Myers

I have a York system about 3 years old with separate units for down stairs and upstairs, and installed when the house was built. After noticing low air flow I opened the access panel on the air handler cabinet and noticed the blower was spinning very slowly.

Turning unit off I spun the blower by hand and it spins freely and quietly. The symptom is the same whether I have the unit set on "Auto", "Cool", or "Fan Only". It is a direct drive blower and based on the labeling appears to be multi-speed.

I know York has had problems with coils and we have had the coil replaced twice on the downstairs unit already; but the blower seems to be the issue on the upstairs unit. What are my trouble shooting steps?

On 2017-09-13 by (mod) -


I am not smarter than your onsite technician. But I suppose the tech thinks the motor for your air handler blower was over-worked.

On the face of it I'm surprised that a new heat pump would require new air ducts unless you were completely redesigning the system and its capacity.

Keep in mind that some techs can be smart at HVAC equipment repair but not good at communicating clearly.

On 2017-09-13 by Kay

No air was blowing from our heat pump. Techician said the motor was burned out and we need a new motor. He said it probably happened because when they put the new heat pump in 2 years ago they didn't put new air ducts in, so our old ones are probably too small and made the motor burn out. Could this be true?

On 2017-09-07 by Laura

Heat pump free is ice anywhere inside unit or outside...blower works great... inside unit clicks once loudly..but will not come on what is the problem?

On 2017-09-06 20:44:46.621313 by Anonymous

I need the answer

On 2017-09-06 20:39:37.748869 by Chong. Willey

Gas furnace it has a block Dusty blower

On 2017-09-06 20:37:43.578876 by Chong. Willey

Gas furnaces and block Dusty blower

On 2017-09-01 15:45:32.085777 by (mod) -

The motor may be a single speed machine. Did you check the data tag?

Low refrigerant can also cause coil icing.

On 2017-08-30 23:49:54.284803 by Skip

Blower motor speed will not change. I have a freeze-up issue with the A/C not that the refrig has been replaced. The filter and evap are clean so I believe I'm not pushing enough air thru the evap. In testing my blower motor it seems that no matter how I wire it, it runs at the same speed (3-phase, 4-sped options). I checked the resistance of each winding and they read in appropriate steps - but my ear tells me the blower is running at the same speed on the low setting as it is on the high. Any ideas what would cause that?

On 2017-08-04 21:34:46.310958 by Bill

Air handler fan does not start up immediately. It will hum for awhile and then finally start up. After it gets started, it runs rather well. Any suggestions? Thanks

On 2017-06-23 01:07:14.745303 by jeff baker

Problems w bryant cenral air started w blower motor going out followed by compression motor going out

On 2017-06-15 01:48:52.876709 by Phillip

I have a new Rheem air handler with a d/c blower motor. The fan spins slowly and stops and goes on and off quickly???

On 2017-06-13 12:55:35.484785 by (mod) -


Most-likely you bumped a plug-type wiring connector and loosened it.

With power OFF to the unit, you can remove the cover and look for wires to the fan motor - follow those to see if there's a disconnection.

Assuming that the fan and condenser/compressor unit was working last time it was used, and that you had power off to do your cleanup, it's not likely that there is a fan reset button problem; the reset on a fan motor trips if a motor overheats; not all fans have such a button as some thermal overload resets are internal and will re-set themselves automagically after the motor cools down.

On 2017-06-13 12:52:18.578131 by Anonymous

I took the top off my central air unit to wipe the wet leaves, & dirt out i put the top bacon i tried to be careful & now it has power but fan doesnt urn did i maybe bump a wire plz help me its so hot i dont h $ right now is there a reset button

On 2017-06-12 17:39:04.716306 by (mod) -


Also check for a bad door safety interlock switch on the access compartment door to the blower.

On 2017-06-12 16:28:36.798985 by George

Have a blower motor that won't start.
1) Ran 120 VAC to connections on motor, motor spins up fine.
2) Pulled the controller board, thinking that this must be the problem, after looking at the Board diags, wasn't sure and put it back.
3) After installing the controller board, 2 slow blinking lights which diags say indicates it is on. (Motor still won't start)
4) Checked Drain Pan - Empty, checked the line, no blockage.
5) Cleaned Filter

Not sure where to go from here.

Any thoughts?


On 2017-06-06 21:34:53.708423 by (mod) -


I can but suggest double-checking the thermostat wire connections, as I'm guessing nothing else changed and that the blower was working before the change.

On 2017-06-06 14:55:25.126420 by Greg

I just put a new thermostat in my house now my blower motor won't shut off any ideas?

On 2017-06-05 20:46:27.265801 by (mod) -


If the slow speed you cite is definitely the fan itself (not a blocked air filter or crushed air duct) and considering that you haven't changed anything (like a fan speed setting on fans that permit various speeds), then most-likely the fan motor has a bad start/run capacitor.

You can search InspectApedia for HARD START MOTOR CAPACITORS to read details. Take a look and then ask more questions as you like.


On 2017-06-05 18:30:44.406364 by Jeff s

I have an old carrier day n night comes on but the blower does not ramp up,it only seems to be running at swamp cooler type cant put enough air thru evap core to keep it from icing up

On 2017-05-28 19:51:21.975377 by jessoskaggs

my American standard 16 seer ac is good but the blower running is louder than when installed 5 yrs ago

On 2017-05-27 00:53:54.067806 by (mod) -

IF the motor has an internal thermal overload protection it will self-reset after the motor has cooled down. Leave power off for 15 minutes or longer.

If the motor has voltage delivered at its terminals and doesn't run after that, the motor is shot and needs replacement.

On 2017-05-27 00:02:09.428156 by percy

No blower fan reset button on my heatpump. How so I reset it?

On 2017-05-16 22:42:40.267794 by (mod) -

that sounds like a bad start/run capacitor on the fan motor

On 2017-05-16 22:04:14.273730 by Tony

My window air conditioner fan is having a hard time coming on. If I spin the fan it does slowly comes up to speed.

On 2017-04-21 21:22:12.316236 by (mod) -


CHeck out the diagnostic suggestions at

On 2017-04-21 13:56:56.636625 by Rodney

I have a 3 ton York unit 2 years old. the blower fan will not run. I can kick the disconnect off and back on and the fan will come on and run for maybe 5 seconds and that's it. It will not run when turning the thermo fan to run position either. do I have a bad copasitor?

On 2017-04-16 18:36:25.846598 by (mod) -

It was smart to check the condensate pan/drain, particularly if there is a sensor switch in the condensate tray that thinks the tray is flooded.
If the fan runs on manual but not in response to the thermostat I usually start by eliminating the thermostat by disconnecting its wires at the air handler, then jumping the TT terminals at the air handler - that's the same effect as if the thermostat were calling for the air handler to run.
Assuming there's power at the air handler, if that doesn't start the blower then I suspect a bad relay or control board.

On 2017-04-16 17:24:47.091622 by Jack

Tried to fired up my AC today but blower won't come on. Outside unit is working and fan is running. If I run the blower fan itself it works fine and also works fine with heat. Not with AC turned on. I have cleaned the drain pipe but still nothing. What could be wrong?

On 2017-03-27 21:04:00.513665 by (mod) -

Josh I don't know. But you can rule the thermostat in or out by disconnecting it at the air conditioner. Jump the two thermostat terminals together at the air conditioner - the same as if the thermostat were calling for cooling. If the system runs then the issue is the thermostat or its wires.

I suspect a bad or failing electrical connection or control board or relay.

Watch out: stay away from live voltage -the risk is death

On 2017-03-27 21:02:51.762467 by (mod) -

AUTHOR:Josh (no email)

COMMENT:Okay so my thermostat goes down to 71 in the morning but it's hot inside . A/c runs fine. The blower continues to blow for a day then next day acts fine. Then next day goes all day until night time then works for a few hours cycling then won't shut off again. Is it the thermostat or bad relay ?

On 2017-03-04 18:19:29.593644 by (mod) -

The blower fan will run for a while to extract remaining heat from the heat exchanger - to cool it down. Otherwise if the fan stops while the steel heat exchanger is still quite hot, it could crack or otherwise be damaged.

On 2017-03-04 03:38:55.659624 by Anonymous

Why would my heater unit keep blowing after the unit shuts off

On 2017-03-04 03:34:31.097854 by Anonymous

After my heater runs it's cycle and cuts off the fan slows way down but doesn't completely stop

On 2017-02-21 23:57:03.473799 by (mod) -


Usually a pulley is pushed onto the motor shaft and is secured with an allen screw or set screw. But if the pulley you ordered won't slip onto the shaft where it belongs one would need to replace the shaft, motor, or blower parts. YOu could try filing the shaft but I worry that if the pulley is askew the system will stress the motor or blower and lead to a new failure.

On 2017-02-21 19:08:02.371903 by Stacey

I have an old (1965) Luxaire furnace with a Westinghouse blower. There was a terrible noise yesterday, I found the large pulley had fallen off. We couldn't get it back on. Looks like the threading is stripped. Ordered a new pulley from Grainger. There is no threading on theirs. Grainger said, that is how they are now. I can get it lined up but it won't go on past the first thread. Any tips or ideas? I am alone with a 4 year old & it's chilly!

On 2017-02-03 19:32:59.283147 by Denis

When I start my a/c at the end of the evening my evap blower motor can take up to 20 sec. before starting. Afterwards, it runs normally. Should I worry about it ?

On 2017-01-22 19:49:39.822021 by (mod) -


You need to find the cause of the short circuit and to see if that damaged other wiring, equipment, controls or tripped power to the unit that's not working.

On 2017-01-22 19:49:01.545642 by (mod) -

Mike said:
Hi I have a uniTrane Fan Coil and Force Flow Unit ... I had a short circuit on a wall plug near by the unit and the unit is not blowing air. What could be the issue?

On 2016-12-27 20:37:16.582817 by (mod) -

Good question T

A bit of end play when moving the blower motor drive shaft in and out of the motor - that is, along the long-axis of the shaft - is usually OK but if there is lateral p lay - you can wiggle the drive shaft from side to side in the motor, then the bearing(s) is (are) shot.

On 2016-12-27 20:03:54.296296 by T-bone

Should there be some travel on the shaft of the blower motor?

On 2016-12-19 02:09:32.567947 by Anonymous

Fan on top works blower works but no heat or air coming through the vents

On 2016-11-12 23:10:33.739514 by Sanita

A recently installed blower motor on my furnace continues to run long after the furnace shuts down & the only way to stop it is to shut off the main burner switch! Why?

On 2016-10-23 01:20:35.173238 by David pope

Blower motor runs fine with ac but won't come on with heat

On 2016-09-30 17:33:36.183452 by Trivil

Hey my split system will operate properly for 20 minutes then it will randomly shut off the entire unit while still calling for cooling . When I turn the fan into on position, still won't operate. But if I allow the unit to remain off for a couple of hours then restart, it will have the same results. No pressure switches are installed on the condenser/compressor, and I don't have 24 volts coming to the condenser. My question is can the overload shut off for the blower cause the condenser to not come on because the blower motor circuit is open? I never had to reset any breakers,unit resets itself. I'm going to check amps on blower today with only fan running to see if the blower is over amping. Any suggestions are very much appreciated!

On 2016-04-24 11:09:26.347495 by rehan

Gibson ac working good cooling good but after 2 hours cooling it will slowdown and the cooling also reduce. what is the problem

On 2015-10-19 04:21:43.036521 by Jamie

I have a colmen evo gas furnace furnace kicks on blower wont run I pulled the blower off and hooked 120 to it blower works fine what else can I check


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