Recent HVAC blower fan testing & diagnostic questions & answers: set #5.

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.

HVAC Blower Fan Test & Diagnosis Q&A 5

The questions and answers discussed below were posted originally at BLOWER FAN OPERATION & TESTING - please be sure to read that collection of diagnosis and repair steps.

Air 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.

Also see BLOWER FAN OPERATION & TESTING

Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE - home

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.

See ELECTRIC MOTOR OVERLOAD RESET SWITCH

Marco:

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

Hoa

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

Reply:

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.

See AIR CONDITIONER BTU CHART

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?

Reply:

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.

Kevin,

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 ?

Reply:

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?

Reply:

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.

Peg:
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?

Reply:

Jeff:
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.

Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE

and CAPACITORS for HARD STARTING MOTORS

(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!

Reply:

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;

Then see COMPRESSOR / CONDENSER DIAGNOSTICS

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

• COMPRESSOR / CONDENSER REPAIR - home
• DIAGNOSTIC GUIDE A/C or HEAT PUMP - home

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

Reply: if your air handler blower fan assembly drive shaft wobbles

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.

Patrick

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.

...

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Or see BLOWER FAN OPERATION & TESTING FAQs-6 - more-recent questions about why the blower fan won't start, won't stop, squeaks, roars, rattles, or is weak

Or see these

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• AIR HANDLER / BLOWER UNITS - home
• BLOWER FAN OPERATION & TESTING

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