Air handler blower assembly(C) Daniel FriedmanAir Conditioner or Heating System Blower Fan Diagnostic FAQs

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HVAC blower fan testing & diagnostic questions & answers:

Reader questions & responses help diagnose trouble with the blower fan or air handler fan used in both air conditioning and heating systems.

This article series discusses how to inspect and test a heating or air conditioning indoor air handler blower fan that is not working. We also discuss convector unit fans and we suggest diagnostic steps for squirrel cage blower fan squeaks and noises.

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Heating or Air Conditioner / Heat Pump Blower Fan Testing & Diagnostic Procedures

Photograph of attic air conditioning air handler, condensate drips on floorAir Handler Blower fan motor RUNS BACKWARDS

The cause of a backwards-running fan (and some other electric motors) could be a bad start-run capacitor

(see CAPACITORS for HARD STARTING MOTORS) or a bad control board. More rare, incorrect wiring or internal damage to the fan motor windings.

Details about diagnosing and fixing a condenser fan that was running backwards are discussed in our companion article on compressor/condenser units, at Questions & Answers about compressor/condenser unit fans.



My Heating Furnace Blower FAN WON'T START & Furnace Burner Shuts Off - what do I do?

Question: the furnace burners go on but the blower fan does not and then the flame shuts off what's wrong?

I have a american standard furnace freedom 80 the burners go on but the blower fan does not and then the flame shuts off what's wrong? - Robert.

(July 18, 2011) Ashley  said:

Hello, My ac unit sounds like its trying to run but no air at all is comming out. It almost seems like th efan isnt turning on at all.

(June 28, 2012) Patty Goeke  said:

We had a power outage today. Now our a/c unit fan cycles on and off quickly. On for 20 seconds and then off and then back on for 5-10 sec. We have the unit turned off now and have called the service person to come out tomorrow, but are stymied as to what may be the problem. The unit is 6 years old and is regularly serviced.

(July 8, 2012) Mike Franklin  said:

I installed a new heat pump and air handler May last year. The external heat pump will come on but the fan in the air handler will not operate. Is there a reset switch?

(July 19, 2012) Marco  said:

Last night I noticed the compressor was running on the Lennox AC unit, but not the blower. Off-On several times, etc. nothing.

This morning I opened the access doors, checked the fuse near the door switch, OK. Then checked the condensate water pump, it was full, cleaned it out, checked that it worked. OK. Put everything back, and now nothing works. Opened the doors again, manually pressed the door switch and heard a click, then some green lights on the PC board there, then they went off and a red light started blinking, somewhat slowly, like once per second. Any thoughts?

Reply: the fan limit switch is turning off your heating furnace burner because the fan is not starting. Diagnose and fix the blower problem.

Robert, if the furnace blower fan will not start, the limit switch on your furnace will turn off the burner in order to avoid overheating and damaging the heat exchanger. You'll need to inspect and fix the blower fan problem. If your furnace blower uses a drive belt to connect the fan to the driving motor check that the belt is in place and not slipping. Other blower fans use a direct drive motor whose shaft spins the fan assembly. IN either case check that the motor is starting;

Ashley, If your indoor air handler fan won't run and the thermostat is calling for cooling and the outside compressor is starting up normally, check for lost power or power off at the indoor unit; check for a fan motor reset button popped out; check for a blower fan driven by a pulley and belt with a lost, loose, or broken fan belt;

Patty: A power surge can kill a circuit board or on occasion damage a motor. It's possible that that cycling you describe was the compressor motor unable to actually start and run - your tech will probably look for something visually obvious and then often s/he will try swapping in a new start/run capacitor.

Mike: Mike, check power, and look for an open blower compartment door safety switch or condensate overflow pan switch. After those obvious sorts of checks, move on to the start run capacitor, loose wires, bad circuit board. And of course a bad or stick motor.

Mike if the motor has it's own thermal overload manual reset switch you'll see the red button popped on the motor body. Many have a thermal overload that has no button but auto resets when the motor cools down.



Watch out: I would TURN OFF THE SYSTEM all electrical power IMMEDIATELY if you have not already done so. You are describing an electrical problem that could be unsafe.

I agree that a blower fan that is not working can, by moving little or no air across the cooling coil, allow the coil to ice up. You need a service call from a trained HVAC tech who will check the wiring, fan motor, etc.

Question: adjusting blower fan speed in an air conditioner, heat pump, or furnace system

How do you adjust the blower gas furnace to speed it up a little bit? The reason is that I'm adding 300 sq feet. Also how do you open the cover of the cooling coil? - Hoa, 8/16/11

Reply: How to increase the heat output from a gas fired furnace or cool air output from an air conditioner


If there is no removable access cover to give view of the cooling coil then a technician would have to cut away sheet metal to give access. That's not uncommon. A new cover is fabricated and screwed or taped in place afterwards.

While dual speed or variable speed fans can run at different RPMs and thus vary the delivery of air through the system, you can't speed up a one speed blower fan. But you can increase air output from the system by several measures:

- increase the return air provided to the system by adding more return ducts
- be sure your air filer is clean, not blocking airflow
- add booster fans at individual supply or return registers

As long as the total BTU requirements of the building don't significantly exceed the BTUh rating of your gas furnace (or air conditioner or heat pump system) you should be OK.

Reader follow-up:

Thank you for replying! I live in California and my concern is about the cooling system. The house I bought is 1-story, about 1500 sq ft. (originally, this house was 1100 sq ft but an extra room was added to the back of the house). What should I do to connect the air ducts of this new room to the original-sized air ducts in the rest of the house?

Also, the outdoors AC unit and indoors furnace are close together and they are two tons. Is it ok if I replace the furnace and cooling coil with 3 tons? 8/17/12


Hoa the duct question needs to be answered by an on-site HVAC installer with some expertise and experience - I simply can't know enough from simple text Q&A to give a solid answer to sizing, routing, placement of registers, etc.

About changing the total BTUH rating of your cooling system, I would NOT change the total BTU capacity without discussing the heating and cooling loads of the whole house with an expert. If you make the new system too big, that is, provide an air conditioner with too much capacity for the size of the home, the unit may cool the air but it won't dehumidify properly, you won't be comfortable, and the short-cycling of the larger unit caused if an oversized unit is installed can damage the equipment.


Reader Question: FAN WON'T STOP: air handler keeps on running; evaporator fan keeps running, gets hot, turns off

outside compressor comes on and off house is cool. the air handler keeps on running sometimes for a couple of hours. Anon 5/14/11

(May 26, 2011) Jason  said:

I have a similar problem, the outside condenser is working fine but the evap fan will not stay running. It will run for about a minute and gets very hot and turns off. I have repalced the capacitor and not help, and ideas?

(July 8, 2012) J. D'Angelo  said:

Air runs good but fan never turns off

(July 11, 2012) kevin lamb  said:

my american standard a/c will not turn off

(Oct 10, 2012) Peter  said:

My A/C is off and my blower refuses to shut down ! I tried taking out the battery , I tried raising the temperature what else can I do??

(20 hours ago) Rick  said:

My heater and blower work, but when the heating cycle shuts off the fan keeps blowing cool air, have to turn the thermostat down to get it to shut off, I can't find anything on the internet that discusses this type of problem, anybody have any recommendations?


Not sure but it could be a control board problem. I'd ask for a service call. Let us know what you found - it may help other readers. See the diagnostic article found at FAN WONT STOP - LIMIT SWITCH

Jason if your indoor blower compartment fan is overhreating it sounds as if the motor or a bearing may be failing. Often a failing electric motor produces an early warning when its starter capacitor fails repeatedly. If you are qualified and can do so safely, check the amperage draw against the motor's data plate specs. Watch out: electrocution hazards.

J.D. check for a control at the thermostat or at the limit switch that is forcing the fan to ON mode. If that's not the trouble check for shorted wires at the control or thermostat.


if an A/C unit won't turn off start by setting the thermostat set temperature to well above the room temp - satisfying the thermostat. If the equipment still won't turn off either someone left the fan switch in manual "on" or there is a control or board problem that needs to be repaired - in that case I'd shut off the equipment and call my service company.

Sure, Rick. Thanks for asking. We have an article on how to diagnose and fix forced warm air heat when the furnace fan won't stop when it should. Just see FAN WONT STOP - LIMIT SWITCH

Reader Question: AIR NOT COOL enough

(May 27, 2011) van  said:

air coming out but not cooling enough , refill r22 last year. how to fix it ?


Van, if your A/C is not cooling enough and you had a refriger4ant leak last year and you added refrigerant, a fair guess is that you have a significant refrigerant leak that needs to be found and corrected. The bad news is that as R22 is no longer in use a complete conversion of the A/C system to use a modern refrigerant may be in order. So before spending on costly repairs to the old system you might want to consider that option.

Reader Question: WEAK AIR FLOW , air temperature not right

(June 3, 2011) Leanne Kidd  said:

I am at my wits end with our unit. We have gas heat and a pump for our air. The unit was replaced in August of last year, the fan was replaced in July 2010, and we had some duct work done in November but none of these helped our problem. We have had 5 A/C guys come out here and no one can seem to tell us why it is still not working. Cold air comes out of our ducts but not strong enough. We run fans in every room all day and night and it is still 85 to 90 degrees in our house all of the time. We live in Alabama and no central air is just not an option for us. Can anyone help?

(June 5, 2011) peg  said:

Mine is doing this same thing - it seems no one understands me when i say the strength of the air coming out of the registers is barely there at all. I have come to the poin where i believe its just dirty in the evaporator (plenum?) but mine is sealed above the furnace seemingly not accessible - so how does one clean this up without a service call costing hundreds of dollars (which at present i cannot really afford - so next option is wire a 220 outlet to place my window unit in for some relief till things get better for us)

(July 10, 2011) ryan  said:

hi joe, my A/C is running but the wind is neither cold or hot. i've look out the compressor, but it seems my motor fan is not running. i am afraid it may be caused by condensing coil or the motor itself is not working. can you advise me which part should i go through first?

(Aug 15, 2012) Rex  said:

My my heating/ac system does fine but the vents don't seem to blow much air out, i was wondering if i installed a bigger blower would that hurt my heating/AC system?


Leanne, from your comment I sure don't want to pretend to be smartger than 5 A/C guys you've had on the site, but from your description it sounds as if there might be a supply or return duct design problem that needs to be understood and corrected. I'd ask for an experienced HVAC tech or engineer who can look at the system layout, ductwork, etc.

Assuming that we are not talking about an air conditioning system design problem (such as airflow has ALWAYS been inadequate), then if the air flow at your supply registers is weak there are several possible causes; among them, things you can fix yourself may include:
- a dirty air filter
- air ducts that have become crushed or disconnected
- air supply register controls that are in the "closed" position
- an air duct damper that is closed or partly closed

Other problems like an icing coil or dirty blower fan (dirty blades reduces airflow) are repairs for which you'll need a service technician

Reader follow-up

We have done some research and think the same thing. My husband is going to check into a possible disconnect in the duct at the main source to see if there is anything wrong. I was looking at the air duct section on here and found someone who was having the same problem and that was his issue. And Dan as far as being smarter....Well no one else has been able to figure it out so I would say that your advise has been the best so far. :-) Thank you.

Reader Question: where is the blower motor RESET SWITCH ? Check the capacitor?

(June 15, 2011) Jeff  said:

There is not a reset switch on my blower motor. do you think it is a bad capacitor keeping the fan from running?


Indeed many electric motors do not have a manually resettable overload reset switch ( ELECTRIC MOTOR OVERLOAD RESET ) ; If one of these motors won't start, and presuming that there is power to the unit and all else is operating normally, I'd suspect a bad capacitor or a bad motor itself. If you can spin the motor manually (with the power off so as not to get injured) then it sounds as if it's not seized and I'd try a new capacitor.



(June 16, 2011) Jeff  said:

Thanks! I will call a AC tech for that but I will suggest that to them. Thanks for the very informative site and the feedback.

Reader Question: Inside air handler runs, outside COMPRESSOR/condenser DOES NOT START

(June 20, 2011) Canton John  said:

Home central AC outside fan not turning on. I can hear the blower in the basement. No cool air at registers. Checked fan outside. Fan does not turn on. I poked at it manually and it seems to move, not seized up. What should I do?

(Aug 4, 2011) mellian  said:

Central Florida: The squirrel cage can't seem to get up the energy to kick in. We can hear it "thump" trying to start and the coils froze up while we were gone today. We had this same problem last year and had a part replaced. The tech gave us a huge runaround about the part going bad on Trane units (our unit is 8 years old, 3 ton, 12 Seer). I want to say it's a capacitor of some kind, but I'm not sure. He had to call all over central florida to get a part for us and acted like it was a big deal that he found a "refurbed part". He had strongly suggested we buy a new air handler. I find that hard to believe for a unit that was only 7 years old at that point.

Anyway... the fan/squirrel cage is doing the same thing now and we really don't have the 900 bucks for another one of these parts. Are you familiar with this? Do you have any suggestions? Do we need a new air handler?

Thank you!


Canton John: if your outside compressor won't start, first check that you are calling for cooling at the thermostat, and second that there is electrical power to the unit;


Mellian: when the blower fan is having trouble starting, before replacing it I'd try replacing the start/run capacitor, or installing a hard-start capacitor. Those parts are as common as dirt - every HVAC supplier stocks them.

See CAPACITORS for HARD STARTING MOTORS or see these two diagnostic articles

Reader Question: Noisy LOOSE wobbly BLOWER FAN shaft

(June 25, 2011) Brian H  said:

Old Amana blower shaft is wobbly. Do these shafts running through a squirrel type blower unit start to bend or get out of balance? If so, what do I need to do to stop the pully from looking like a warped wheel when running?; replace with a shaft? What causes this? Finally, how do you know what the correct tension of the belt should be from the motor pulley to the fan pulley? Many thanks in advance. I cannot get a good honest answer.

(Sept 4, 2012) Jay  said:

i have 2 separate heat handler motors, one squirrel cage seems out of balance? it's noisy but not all the time? i have a tech who wants 450.00 just for the cage??? and that doesnt include the motor??? wow maybe it can just she cleaned?? he never looked just wants to prelace ir cage??

(Sept 19, 2011) pat  said:

My a/c fan fell off! When reinstalling it should the air flow be into the unit or out? I hope we put it on the correct way!

(Sept 29, 2012) patrick  said:

i have a problem with my air condition when switched off the internal fan moves free but when switched on it jammed in a certain position


Brian H: if your air handler blower shaft wobbles in the bearings you need to either replace the whole blower assembly (which is what most service techs will do) or replace the bearing assembly and blower fan shaft (labor intensive too). I'm assuming that your description of the pulley looking "warped" when the system is running confirms that the bearings are shot. But first check that the pulley is mounted square on the shaft and that the pulley is not loose. Many fan belt pulleys include a metal key that locks the pulley to a slot in both pulley and drive shaft; the pulley can be loose, wobbly, and still turn the shaft; the pulley is tightened to the shaft with an allen screw.

Jay, check for a loose bearing or bent, damaged blower fan assembly; It should be possible to replace just the squirrell cage fan assembly and bearings if that's where the problem lies. If the tech's bid includes labor it may not be way out of line; I suspect the part is less costly than that. Ask for clarification.


Check for a loose or damaged fan motor shaft or shaft bearing or loose connection of fan blades to the motor shaft. I suspect a damaged motor or shaft.

Reader Question: HVAC blower acts crazy, seems to be trying to cool and heat at the same time

(July 6, 2011) Zack  said:

Ok, hopefully someone can help me here, my blower isnt working, which is no big deal to replace, but my whole unit is acting crazy, its calling for heat and air at the same time??? could that be due to the blower motor not working???


Sounds like a control board circuit problem; check the thermostat settings and if they look right you need a service call.

Reader follow-up:

I have someone coming to look at it tomorrow, but when I talked to him, he said that it is possible that the motor being bad could cause that, I don't see how but I was just wondering if its possible? - Zack


Zack, certainly no one of us knows all about anything. But I don't understand how a bad blower motor would call for heat and air at the same time. A bad blower motor ought to mean that air stops being blown through the ductwork. The absence of cooled air would be sensed by the thermostat set in cooling mode and the TT would never be satisfied - it would keep calling for cooling. (When a blower stops the coil may ice up, further stopping air movement). I don't see how that would call for the system to switch to heating mode. Is the service tech arguing that your system switches to heating mode because it's detecting an iced cooling coil? Let us know. What you're told will surely help other readers.

Reader Question: A/C runs more and more often and I smell burning

(July 26, 2011) Mark  said:

My A/C unit is kicking on and on more frequently and smells like something is burning up. House maintains temp


Watch out: Mark: if you smell something burning at electrically powered equipment I'd turn it off immediately and hire a qualified technician to investigate the problem. The risk is that the overheating is ignored and you have an electrical fire.

Reader Question: Central Air Blower fan gets hot and stops

(July 29, 2011) Barbara  said:

my central air unit is is 30 years old...the fan gets hot and stops...after it cools down it will start up again..had new fan installed and it does the same thing...the fan just hums after about 10 mins of cooling...where do I start or should I just look for new unit?


Barbara it's odd that a new fan motor would overheat and stop running unless
- the temperature is actually within normal operating range and it's a start/run capacitor that's failing
- there is a wiring or other problem causing abnormal overheating.

Are you sure it's just the fan motor and not the compressor that's overheating?

Reader Question: A/C doesn't work right, poor cooling - ducts too small?

(July 31, 2011) David W. Hesson  said:

I have a real problem. I bought a new heat pump about 4 years ago and the a/c portion doesn't work the way it is supposed to. It might be, say 74 degrees in the house and then I move the thermostat to 72 degrees, The temperature in the house goes to 75 degrees and stays there.

But sometimes if I only move the thermostat 1 degrees the a/c might cool the house down 1 degree. This has been this way since we bought it Dealer has been out here 6 or 8 times. He always finds something wrong. Too much freon, not enough, wire off thermostat etc.

The one mechanic who appears to have the most sense say our air return duct is too small and we need a bigger one. They offered to put one in for $200. I say it should have been fixed when unit was installed. Plus no other visit has fixed it. We live in Virginia. This has really been frustrating. Please help


David those explanations about A/C troubles leave me confused.

If the air coming out of your supply registers is not cool the system is not working and it's more than a duct problem.

Take a look at the article titled DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP - that you can find on this page at Continue reading where you will find an INDEX to RELATED ARTICLES that includes a live link - for some suggestions that might get us on track, and ask for an experienced, senior, trained HVAC tecnician

If there is no air coming out of the supply registers that's often a fan or filter or duct problem, or a cooling coil blocked by ice.

Question: Fan Motor Failed, Froze Coil, Repaired, Now Blower fan & AC work only if fan is set to FAN ON, does not work in FAN AUTO position

My parent's furnace fan stopped working while they had their A/C running. It resulted in freezing up the A-coil and a wet mess. They still have their original Honeywell T89F Zone Thermostat.

With the thermostat set to "COOL" and as long as you have the thermostat set to "FAN ON"... the A/C will work and regulate temperature properly. But as soon as you move the switch over to the "AUTO" setting, the furnace blower motor stops and the outdoor unit still runs regardless of how low a temperature setting.

Manually operation the A/C is a bit of a complicated chore for a couple of 90 year old parents. Can you give some pointers to help them out? - B.C. Ohio, 7.21.2014


I take it that the fan was repaired after it stopped working.

It seems unlikely to me that a fan failure would have damaged the thermostat itself - and as you are confident it was working properly previously with FAN AUTO set then

I infer that the thermostat re-wiring to drive the fan was not properly done.

So I'd start by calling back the repairman to fix the mis-wiring.

Meanwhile you could simply leave the fan on 24/7 in the FAN ON position. That will result in more even house temperatures and improved air filtration at a little increase in electricity cost.

The thermostat should still turn the A/C cooling system on and off in response to temperature.

Try that and keep me posted. - DF


(Aug 20, 2011) Steve said:

When I turn our central AC unit off the blower stops, but I hear a noise like another fan or blower keeps running.

(Sept 5, 2011) Cindy said:

We have been experiencing intermittent delays in the blower motor coming on after the compressor starts. We have had two repairmen out to look at the system. The first could find nothing wrong and told us to call back if the blower motor does not come on at all because if that happens the coils could freeze up and the whole system would go out. The second repairman cleaned the compressor again, which is something my husband does regularly anyway, and added two pounds of freon. This has still not solved the problem. It seems to us that this behavior should be an early indicator that something isn't right within the system. I am looking for a suggestion as to what might really be wrong with our air conditioner.

(Sept 20, 2011) Wesley Erickson said:

my air handler fan keeps running. someone told me it could be the contact switch stuck. is this a easy fix ?

(Dec 4, 2011) Bob said:

When My Weil Mclane boiler blower shuts down after reacing thermostat temp, the boiler unit shakes. the blower motor seems fine with no noise....... is it the blower unit or the motor with a work shaft? how to check? boiler is22 yrs old.

(Apr 27, 2012) Diane said:

It rained every heavily and the fan or motor sounded like it was having a hard time kicking in. I turned it off for several days thinking that it was wet and needed to drt out. It still does not blow or heat. It is a dual window unit. Heater/Air Conditioner. Whay should I do before calling a repairman?

(July 18, 2012) Paul Galante said:

The blower isn't vibrating it just that the blower makes a lot of noise



It may be useful to track down just where the noise is originating, more precisely - to a motor, a loose mount, a rattling duct, etc.


(July 19, 2012) george said:

we came home from a trip. before coming in double wide mobile home i was wattering my dog. i saw ice on outside unit line going into home, wife said insde coile were frozen badly, i came in and it was. i saw squrile fan was turning, but slow. i turned it of an spunn the fan and it spun easy and fast, after turning it back om it was still really slow, so i took off bottom cover where breakers are and turned em on an off , fan still slow, after doing this several times i saw electricle sparks on left side of fan motor. turned it off an on , it sizzeled then stoped , but fan still ran @ slow rpm. please tell me what you think.

(Aug 6, 2012) Anonymous said:

Sticker says the control board has been integrated with the blower motor.
Do i need to remove the entire motor now?


Will the blower stay on if you set the thermostat switch to
Fan on or manual?

If so take the thermostat out of the circuit and then check for a loose wire, sensor, or control board or relay


(Aug 21, 2012) Eric ...eric.rodney@doe.state.nj said:

When either the furnace or air condistioner are on the noise level from the blower is extremely loud overpowering conversation. Is there anything that can be done? Is the location of the furnace, proximity to the register and afdjoining room a factor? help.

(Aug 22, 2012) Nancy said:

I just replaced the fan motor and capacitor on my condensing unit but haven't turned it on yet because someone told me to make sure there is only 1/4 " between the bottom of the motor and the fan blades (stating it will perform best) and that I should break off the screw ends to accommodate this. I have it placed about halfway down the rod coming out of it that the set screw tightened to, which seemed a safe distance for the blades to spin. Please advise if this will help or hinder my operation.

(Sept 4, 2012) Chris Lent said:

I am changing my blower motor and I can't get the old one off(shaft is stuck, motor won't slide out...I already did a no-no by using as a hammer to try and force it out...someone told me I needed to use a crescent wrench and give it a turn and it should slide out easily..? I don't see how I can get a crescent wrench into the space the assembly allows?

(Oct 11, 2012) Debbie said:

I have a central heater that the blower won't come on. However, if you turn on the A/C part, it works! What is happening?

(Oct 29, 2012) Brandan said:

I have just recently hooked up a new thermostat on my unit. My unit is a American standard runs off of propane. How do I now if it is a heat pump or the heat pump was never hooked up and it's just running like a furnace. I have is set on reg. not heat pump. It heats. When I turn it to heat pump the fan turns on which does not turn on when it's on reg. when on the burner light and the flame shoots down the tubes and all other burnt gasses go out the top. Then the unit kicks on and heats the house. The only reason why I think it is a heat pump is because the propane line Hans a union and seems like it goes somewhere els? Is it a heat pump or it's just not hooked up for it?

(Nov 6, 2012) david said:

my heater fan pops on and wont cut off blowing cold air. I have to throw the circit breaker to cut it off. Even then when I cut breaker back on fan starts running again? So I cant use my heater

(Nov 15, 2012) Bryant 355AAV Blower to high spe said:

I have an older home converted to forced air. The old fixed capacity furnace pushed air to the second floor better than my new variable volume blower. I have the Bryant Evolution thermostat fan setting on high but it sure does not run on high very often. It still runs low and medium and goes to high if not satisfied in a certain time. Meanwhile I am not pushing air to the upper floor. Can this thermostat be programmed differently? or can I buy a simpler thermostat that will drive the fan to high speed?

(Dec 27, 2012) Rodney said:

About a year ago we had our Air handler replaced in the attic with a new one because we had mold blowing out our vents. Now all of a suddened it stopped working and i found a wire melted in half where it was connected inside the unit in the attic. What would cause that and what should i check before connecting the 2 wires back together. No breakers was tripped.

(Feb 3, 2014) Anonymous said:

fan on outside unit works. fan in heat exchanger does not work. What to lok for.

(Feb 4, 2014) Rick said:

My heater and blower work, but when the heating cycle shuts off the fan keeps blowing cool air, have to turn the thermostat down to get it to shut off, I can't find anything on the internet that discusses this type of problem, anybody have any recommendations?


Sure, Rick. Thanks for asking. We have an article on how to diagnose and fix forced warm air heat when the furnace fan won't stop when it should. Just search InspectApedia for

Furnace or A/C Blower Fan Won't Stop Running

and you will find a link to the article.

I will also add this topic and the necessary link on this page.


(Apr 3, 2014) Anonymous said:

I have a day & night hvac unit. The blower comes on when ever it feels like and blows for a couple of minutes then shuts off. I've disconnected the thermostat that didn't work. What do I do now?


Sounds like a bad blower fan switch, relay, or limit switch. But before replacing any parts, disconnect the thermostat wires at their other end - rather than at the thermostat. That will eliminate calling for heat (or cool) by a short between the wires.

Question: Coleman oil fired furnace blower troubles

(Apr 8, 2014) Anonymous said:

I have a new coleman oil fired furness the burner runs fine but the blower motor starts and stops this unit is made by alpine


Anon I can't quite make out the question - if you mean the blower starts and stops rapidly intermittently when you think it should not, that suggests a bad fan limit switch or a bad thermostat or thermostat wire.

Usually on a call for heat the furnace will heat up, then the blower turns on, and the blower and furnace will continue to run until the call for heat is satisfied at the thermostat. Then the thermostat turns off the burner; the blower will continue to run until the blower assembly has cooled down, then it stops as well.

Check the fan limit switch operation;

Check for a dirty filter causing the plenum to overheat

Check for a dirty blower fan causing the same problem by moving too little air

Question: wobbling blower fan noise - rattling

(May 10, 2014) Anonymous said:

when my air conditioner shuts off it makes a terrible noise. it sounds like the squirrel cage is rattling. what could cause this?



I'd ask for a check by the HVAC service company. If there is excess refigerant entering the compressor it can make a rattling noise and can destroy that expeensive component. If the problem is a loos fan itself that's easy to diagnose by checking the fan assembly with power off. The fan should not wobble.

Question: Gibson gas furnace lost blower speed

(May 22, 2014) Anonymous said:

I have a Gibson kg6rc 100c-16b natural gas furnace that SUDDENLY lost RPM of blower assy and cold air stream droped dramaticaly though there is SOME stream, so fan wheel is rotating and clean. I checked it.


Assuming this is a direct drive unit not a belt driven fan I'd look for a failed motor, bearing, or start capacitor.

Question: blower shuts off after 30 seconds

(May 23, 2014) BErik said:

Blower Motor shuts off after 60 seconds:
I have an older Trane gas furnace / central AC unit. Cleaned the AC coils (outside) yesterday and turn on AC today. Started fine, but after 60 second, blower (inside) shut off, but outside unit continued to run.
Trouble shooting:
Turned Fan ON at thermostat - fan/blower ran 60 seconds, then shut off
Jumpered Fan ON (thermostate wires R to G) - fan ran 60 seconds, then shut off
Turned on AC - outside unit and fan came on, but fan shut off after 60 seconds, outside unit ran
Turned on Heat - heat functions worked normally...burner heats, fan on, at temp burner off, fan off after delay.

Any suggestions on what is shutting down the fan after 60 seconds?


Berik, if you are in heating mode watch the fan limit control switch. If the heater is shutting off at the upper safety limit then air flow is probably blocked, causing overheating.

If you are in cooling mode I wonder if your system has emergenc heaters running.

(May 23, 2014) BErick said:

Looked at this some more. New blower motor replaced in the winter works fine in Med-High speed, but for A/C and Fan-ON motor is on HIGH and seems to be shutting down...I assume on over-temp. Air flow seems good, over temp shut down even when panels off the furnace. I will look at wiring, voltage next.

(mod) said:

Good progress. If you can safely measure current draw that'd be helpful.

(May 23, 2014) BErick said:

I currently have the furnace-side High connected to the blower-motor Med-High wire, like when the heat was on. Operation in the lower speed is working. I was able to measure current draw. The motor is an Emerson M55HXHKP-9722, 115V 14 Amp. Using amp meter, got the following readings: High - 18-20 Amps, Med-High - 14 Amps, Med-Low 10 Amps.

I know the motor should not draw 18A on High, based on its rating. Do you think this means the motor is bad or has failed?

(mod) said:

Yes BE.

Question: motor can't drive fan - overheats

(june 1, 2014) joseph said:

The indoor fan motor is working normal without belt, and i connect the belt to the blower the motor is high amper and become heat, what is the main problem, i also adjust the belt, the alignment, the electrical are okey! Please help



Possibly the motor is failing under load and drawing high current, or a belt-pulley bearing is jamming.

Question: Inter City HVAC BM1912GSPL4 blower noise

(June 4, 2014) james said:

i have an inter-city hvac system installed when i built my home in 1995. the model (and mfr) number on the sticker is BM1912GSPL4. my problem is, the blower fan (squirrel cage) began making noise a few days ago. i found a tutorial which duplicates the sound perfectly and is consistent with it's otherwise lack of symptoms. eg; no apparent vibration, good airflow, no squeals, chirps, stops and starts without issues, etc. on the tutorial, the culprit is two loose blades on the squirrel cage. the tutorial suggests jbweld to repair the loose blade(s), or replace cage. i would like to replace it, but am unable to locate the part. sears says my model number is not in their database. any suggestions?



I'd remove the assembly, take it to your local HVAC supplier, and see if they have a replacement.

Or check for a misread model number.

Keep me posted

Question: Blower fan won't stop running

(June 5, 2014) Drew said:

I have a 1980's Lennox (I am at work right now). AC runs fine, heat runs fine. However when I put Fan setting to ON it shuts off after a few minutes. Outside unit and Main unit - nothing works. And it wont turn back on until after a good 30 minutes or so. It does not do this with the AC on at all. I was previously able to run the "fan on" setting for as long as I wanted. Thanks for your help.

(June 29, 2014) jim said:

Hvac fan runs almost all of the time. I have a carrier thermostat unit appears to be working but?


Jim please see the "blower fan won't stop" diagnostic advice at

and let us know if questions remain

Question: lost cooling, blower gets weak

(July 2, 2014) doug lake said:

i have a self contained a/c unit outside of my double doesnt seem to cool as good anymore/had it tested..everything the blowers get week on these after a while-.there is a big fan on the top.-i checked tube under the home seems ok.blower pressure weak in vents-air filter is clean-


Check for dirty blower fan blades and also for dirty air filter or air leaks. Also check for low voltage or slow motor

Question: where is the noisy blower sound coming from ?

(July 9, 2014) Chhayhour said:

Somebody know, where is the noisy sound come from? Is coming from the cooled air blower? Or another equipments? I am really boring with its sound so much. I don't know how to fix this issue. please help me to fix it!



You can find air conditioner or HVAC sound diagnosis procedures at


If the blower fan motor won't turn ON or is noisy, there may be
a ELECTRIC MOTOR OVERLOAD RESET SWITCH that has tripped off due to thermal overload or an electric motor or voltage problem. Don't forget also to look for other switches that could prevent the air conditioner from even starting, such as a condensate overflow pan sensor switch (
see DRIP TRAY DEFECTS) that can shut down the air conditioning system to avoid damage from overflowing condensate pans.

Question: sparks coming from HVAC blower unit

(July 28, 2014) Anonymous said:

sparks coming from blower


Watch out: Anon"

TURN OFF THE SYSTEM immediately as you are risking an electrical fire.

Question: frozen up air handler and refrigerant piping, burned wires,

(July 31, 2014) Bill Morse said:

I have a Goodman ARUF303016AA air handler. The system froze up all the way to the outside compressor. I shut it down and let it thaw. Turned the fan to ON at the thermostat and got nothing. I found the red wire from Transformer 240V, to the Blower time delay relay, burnt off.

I put a new end on it, hooked it back to the relay, and tried it again. It started burning it again, and started melting the side of the relay. Where should I start looking for the cause? The 3 amp fuse on the control board, that the relay is attached to, did not blow.

I have a new relay/board, but would rather locate the reason before burning up another one. Any suggestion would be appreciated.



When there's a burn-up such as you describe indeed it's essential to diagnose just what component failure is causing the burnup before replacing anyhing. Could be a failed compressor, other motor, relay, control board, etc. I can't offer specific diagnostics from just an e-text, and if it were my system I'd ask for help from an experienced HVAC technician. Keep me posted on what you and the tech find as what we learn will help others.

Aug 25, 2014) Anonymous said:

Dan, Thanks for your input. I have found that with the thermostat set to auto and on cool, There is continuity from red to yellow, green AND White, which tells me the Thermostat is bad. I'm not sure if the blower relay wire burn caused the Thermostat short, or vice versa, but I'll be putting in a new Stat, before trying the new relay.Thanks.

Mod replied:


OR the TT wires are shorted together.

Disconnect the thermostat from it wires completely and really to be unambiguous, disconnect the wires at the air handler end, then check the wires - there should be no continuity between them. If there is then they shorted enroute; if not the problem is on the thermostat end or the control board end

Question: installing a larger fan to improve air flow

9/11/14 Anonymous said:

Can I install a larger squirrel fan in my HVAC Unit to increase air flow?


Unlikely, Anon - as the blower assembly is most likely already physically sized to fit the cabinet.

However depending on your air handler design and ductwork it may be possible to install an dual speed or variable speed blower than can increase air flow.

Before doing so I'd check the various reasons that air flow may be inadequate to be sure that none of those is the real problem.

see weak HVAC system air flow diagnostics at

Question: install a bigger blower fan?

(Sept 10, 2014) Anonymous said:
Can I install a larger squirrel fan in my HVAC Unit to increase air flow?


Unlikely, Anon - as the blower assembly is most likely already physically sized to fit the cabinet.

However depending on your air handler design and ductwork it may be possible to install an dual speed or variable speed blower than can increase air flow.

Before doing so I'd check the various reasons that air flow may be inadequate to be sure that none of those is the real problem.

see weak HVAC system air flow diagnostics at

Question: weak air flow or no air flow

(Sept 28, 2014) Rick said:
Blower motor is running but air is barely coming through vents...any suggestions?

(Sept 29, 2014) Betsy said:
The fan is turning, but the air is NOT coming out!


Betsy look for a disconnected duct or a blocked duct

Rick check for a dirty air filter or the same disconnected ducts as at Betsy's house.

Question: blower fan start troubles

(Oct 14, 2014) Jerry said:
Blower motor will start intermittently I've changed the Tstat and motor relay... not sure where to go from here. Could it be the coil causing this issue?

(Nov 20, 2014) Anonymous said:
my outside fan is not turning. house warm but fan on inside unit constantly on. outside temp between 20-49. should outside fan be running? no problems with unit when this summer.



Anon: see the diagnostics at COMPRESSOR / CONDENSER REPAIR

Question: thermostat troubles

(Nov 3, 2014) Anonymous said:
when I turn the thermostat to auto it will not come on but will work when you switched to on

(Nov 14, 2014) Anonymous said:
My thermostat is set to AUTO, but it ran continuously. I set the heat at 62 and expected it to go off at some point, but it did not. Can you let me know what may cause it not to turn off.

(Dec 31, 2014) Tony Afonso said:
The blower motor on my heating system works fine on manual, but when I change it to Auto, the fan doesn't come ON. I changed the thermostat with no avail. Any ideas?


Anon: see the thermostat setting, wiring, and diagnostic advice beginning at THERMOSTATS, HEATING / COOLING


that Sounds like a wiring error, a thermostat wiringor setting problem or a bad control.

Question: buzzing furnace blower runs intermittently

28 Jan 2015 Anonymous said:

Im having trouble here with my furnace blower. It runs intermittently. Then sometimes it slows down and stops after about 2-3 minutes or so then I hear the BUZZZZZ.

Yesterday I was sometimes successful kickstarting the wheel but later in the day found that this was more difficult to do. It has not seized and seems to only run when it wants to. I replaced the run capicitor and it fired up nicely - then after 5 min back to no fan and a buzzzzz again. Getting VERY little heat from it. WOke up to 56 degree house today. HELP?


Sounds as if there is a failing relay, a failing start capacitor (CAPACITORS for HARD STARTING MOTORS) and maybe ultimately a failed blower motor.

Watch out: if there are loose or arcing wires there may be also a fire hazard; I'd shut it down and call for heating service.

More buzzing sound diagnoses are at

Question: blower air handler fan does not run

(Mar 5, 2015) bobby said:
air handler fan doesn't come on all the time



Check for a loose wire, bad connection, failing relay or control. If you are discussing an air conditioning system check for a condensate tray switch that is shutting down the system.

at NOISY AIR CONDITIONER / HEAT PUMP and at NOISE CONTROL for HEATING SYSTEMS we discuss a range of noises can be traced to air conditioning and heating systems.


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