HVAC blower fan testing & diagnosis FAQs:

Questions & answers on diagnosing and repairing HVAC blower fans in the air handler.

This article series explains how to inspect and test a heating or air conditioning indoor air handler blower fan that is not working. We also discuss fan fan squeaks and noises. The blower fan assembly is the green component in the page top illustration from Carson Dunlop Associates The Illustrated Home.

Heating Air Conditioner Blower Fan Testing & Diagnostic FAQs

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.

The blower fan is located inside a horizontal air conditioning unit in many home air conditioning systems, especially when the air handler is located in an attic or crawl area.

Click to enlarge any image]

On 2018-09-24 by (mod) - whining growling noise at air handler

A good place to start in diagnosing this would be to look at the descriptions of the different kinds of noises and their possible causes, is found in HVAC systems.

This link is a good place to start.

NOISES, HVAC SYSTEM DIAGNOSIS

On 2018-09-24 by Leonard

Air handler can makes intermittent whining/growling noise. A/C is running fine. Might be trouble later, any sugestions?

On 2018-08-28 by (mod) - check out the blower motor

Thomas

A tech would be checking voltage at the motor terminals and if the motor, perhaps taken out and bench-tested, doesn't run then she'd follow procedures

at ELECTRIC MOTOR DIAGNOSTIC GUIDE

or would replace the motor.

On 2018-08-28 by Thomas M

i did that and it did the same thing just a few rotations and repeats. I really dont want to be wrong and throw parts at this and waste more money. And thank you for taking time out of your day to assist me

On 2018-08-28 by (mod) -

Sounds as if something may be water damaged; a bad bearing, bad relay. If (without getting shocked or losing fingers) you give the fan a spin will it start and keep running?

On 2018-08-28 1 by Anonymous

no lose wires checked them all. No capacitor has a wiring harness. There was a good amount of water in the blower wheel so i think it might have slung water around and got somethkng wet. The borad is dry as a bone and no burn marks present

On 2018-08-28 by (mod) - Problem with Carrier ECM Motor

Thomas

Let's start with the diagnostic suggestions at FURNACE FAN WONT START https://inspectapedia.com/heat/Blower-Fan-Wont-Start.php

I suspect a bad capacitor or a loose wire or connection.

On 2018-08-28 by Thomas M

I am having a problem with a carrier infinity ecm blower. Weather I have a call for heat, cool, or just the fan, the fan gets two or 3 rotations in before it stops. Then about a minute later it does the same thing. I am trying to diagnose this issue as my coil has frozen up now

On 2018-02-27 by (mod) -

Yes you are quite right, Bill.

The fan doesn't know what sort of air it's blowing - cold, or hot like some of my explanations.

It's a fan limit switch and a control board that wants to turn the fan on at the right time in cooling and heating mode.

So in heating mode, for example (hot air), if the heat is not working, the plenum never heats up and the blower won't turn on. The fan limit switch doesn't want to blow cold air on to occupants who were hoping for heat.

On 2018-02-27 by BillTheWelder

I want to add that thanks to abnormally warm weather this weekend I was able to turn on the A/C and during this time the blower motor would kick on when set to automatic on the thermostat.

So at this point the blower will not work under auto when set to heat and has to be set to manual to run.

Wouldn't the run start capacitor be required under A/C as well? This makes me think that the thermostat could have failed or been knocked off the wall by my kid again.

On 2018-02-20 by (mod) - With a bad control board it's possible that the blower motor will not run.

Rick

Thanks for an excellent question. I'm answering from the precipitous edge of comptence - that is, I can only give a general reply.

With a bad control board it's possible that the blower motor will not run. In that case, to measure current draw (Amps) of the blower motor you'd have to disconnect it from the control board and hook up a temporary power supply to the motor. Then current could be measured.

By "Reducer" I think your tech is referring to a speed reducer for the air handler blower motor. I'm not familiar with a mechanical speed reducer on residential HVAC;

instead I expect to see a Variable Speed ECM Blower Motor where "ECM" refers to an Electronically Commutated Motor.

That's a more costly motor design that offers distinctive HVAC operating advantages such as quieter motor-operation, ability to fine-tune the motor output to varying conditions, improved humidity removal and more-comfortable air delivery speeds at greater HVAC system operating efficiency.

[ECM driven blowers are provided by Trane (Comfort-R) and Carrier (Infinity Control) and other manufacturers.]

I would never rush to replace the blower motor without some other careful tests.

Ask your tech if it makes sense to try replacing just the control board first or just the motor first.

Let me know what she advises.

Here are some control board test details adapted from suggestions described by highperformancehvac.com - you might ask your tech about this procedure:

Here is the order in which I'd do tests:

- check that power is on to the system

- check that there is no safety interlock switch keeping the blower off - such as the door safety interlock switch on the blower cabinet

- double check every single wire connection, including a check for wires that have pulled loose inside of a plastic connector plug
between the fan motor and the control board - I've found that problem myself more than once

- look for visual evidence of damage such as burns on the board

- if the motor starts slowly that may be normal for an ECM motor design - wait at least 7 minutes.

- check that nobody has bumped a dip switch on the control board, moving it out of the proper settings - compare the dip switch positions to the instructions for your HVAC unit

Notice that none of those steps - where most problems are found - are high-tech.

- confirm proper (24VAC) input voltage to the board

By noting the brand and model of your air handler as well as of the blower motor, if you don't have the service instructions for your equipment, download those from your manufacturer or poke around in our

MANUALS & PARTS GUIDES - HVAC where we have an avalanche of manuals for nearly every brand. Find the troubleshooting tips specific to your equipment.

On 2018-02-20 by Rick Mcgarr

everything working fine today before the annual check up,the tech was leaving and finished but the motor kept on when I asked him if that was normal ,

no he said and after 22 minutes taking things apart and off and back on the tech said the reducer motor and control board are bad,

the only problem is he took the motor amp and blower motor reading and they were about the same as last years reading how can that be?

can you take the furnace blower motor amp reading if the motor and board is bad?

On 2018-02-11 by BillTheWelder

We have a heat pump and recently the blower motor would not come on when the pump would start up.

I've been able to get the blower to come on by switching the setting on the Tstat to manual so I know that the blower itself is fine, what should I check next and where should I look for these parts to check?

A large capacitor was replaced 4 years ago along with a wildly overpriced board about the size of an old school paper flashcard you would use in school for studying.

On 2019-01-13 by (mod) - what to do if the blower fan won't stop running

JM

But here's a tip: if the furnace blower fan won't stop even with the thermostat removed from the wall

I would look first for a fan limit switch (in the furnace) that is set to run the fan continuously

- see FAN ON AUTO MAN THERMOSTAT SWITCH

And also for similar advice you might need to

- see FAN WONT STOP - THERMOSTAT SWITCH

If that's not the problem - that is there is no switch actually asking the fan to run try disconnecting the thermostat wires at the furnace itself - shorted thermostat wires can cause the blower to run.

For a complete diagnostic procedure be sure to review the diagnostics

at FURNACE FAN WONT STOP

On 2019-01-13 by JMed - Lennox G26q3-75-1. Fan blower won't stop

Have a Lennox G26q3-75-1. Fan blower won't stop, even after heat is reached, burner shuts off, and air temp cools.

Does not react to fan 'off' at thermostat, or even thermostat removed.

Replace fan limit switch as readings suggested - same result. Operates just like fan 'ON' at thermostat - no matter what.

On 2018-08-25 by da

Blower won't shut off after ac kicks

On 2018-07-31 by (mod) - air doesn't blow out of the supply registers very strong

sorry Pat Crow I'd like to help but from your question I cannot offer much. If the HVAC blower unit or air handler unit fan runs but air doesn't move out of your air supply registers the fan could be dirty or a duct could be leaky, crimped, or disconnected, or you could simply have a dirt-blocked air filter or cooling coil.

See more-detailed diagnosis and repair procedures

at AIR FLOW TOO WEAK

On 2018-07-31 by patcrow

The fan runs high, medium, and low. All 3 speeds run at low speed, so my room doesn't cool well because the air doesn't blow across the room well. What is the problem?

On 2018-06-13 by Anthony

Indoor unit, just replaced fan motor, replaced contact for compressor, new filter, when I turn my ac on, the fan kicks in and runs for 15 seconds and stops, compressor is still running after fan stops. Unit is not cooling at all now and fan will only run for the same 15 seconds every time I turn it on before the stops. Ideas??

On 2018-02-08 by (mod) -

Sounds odd, perhaps we're missing something from the problem description.

On 2018-02-07 by Anonymous

Had two different furnace people here and they both say it's supposed to run like that there's nothing wrong with my furnace so now it's doing it twice comes on shuts off comes on shuts off comes on runs the cycle shuts off comes on shuts off but that's supposed to be normal I don't know why it's changing on its own

On 2018-01-25 by (mod) - roariing sound at the furnace

Mary

Watch out: I would turn off the air handler and call for repair. My concern, knowing absolutely nothing about your heating system, is the risk of an electrical fire if an air filter has collapsed and been drawn into the blower assembly.

On 2018-01-25 by Mary

When my unite comes on (hear/air) it starts to make a roaring sound when u hear the blower kick in. At first it sounded like something flapping, but now it sounds like the air flow is blocked.

On 2018-01-24 by (mod) - blower motor comes on for a few seconds shuts off then comes right back on

Barbara, in the list of recommended reading OR at the ARTICLE INDEX , take a look

at FURNACE FAN CYCLES DURING HEAT for suggested diagnostic steps.

Let me know if that helps you out or if you have further questions.

On 2018-01-24 by Barbara

My blower motor comes on for a few seconds shuts off then comes right back on runs its cycle to heat shuts off and then comes back on for a few seconds then shuts off until the next cycle it used to come on

Sam for 12 minutes shut off then the would come back on for a few seconds and shut off which is normal for it but today all the sudden the cycle and changed is there something wrong I change my furnace filter last night

On 2018-01-19 by (mod) - blower motor comes on for a few seconds shuts off then comes right back on

Corbett

Your blower fan motor may need a new start/run capacitor.

See HOW to CHOOSE a START / RUN CAPACITOR -

Also check the motor bearings and lubrication

On 2018-01-19 by Corbett McCowan

I have American Standard electric furnance blower wont start some times have to start by hand and it will run fine for about a month and quits have to start again by hand.need answer thanks janicemccowan@ gmail.com

On 2017-12-22 by (mod) -

It might, depending on switch settings. See this article

FURNACE FAN WONT STOP at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

On 2017-12-22 01:11:21.809934 by Gracie

Is the blower suppose to constantly blow.???

On 2017-12-17 by (mod) -

Thomas

Though I don't understand what"a beach box on the island" is, nor what island, (Perhaps the Outer Banks of the U.S. state of North Carolina ?),
still I can offer that
if the fan in an air handler is running backwards you would

1. observe that air is not coming out of supply registers in the home but rather going into them. Hold a tissue in front of a register and see if it moves
towards (in) or away from (out) the register.

2. a service technician, opening the air handler blower compartment can observe the squirrel cage blower fan rotation direction and compare that to the angle of the fan blades.

If the fan is rotating backwards it will move very little air and the biting outer edge of the blades on the round fan assembly will be rotating such that they are not biting into air but rather rolling away from it.

On 2017-12-17 by Thomas

How do you tell if your fan is in "reverse " , mode in a beach box on the Island, OBX

On 2017-08-10 by (mod) -

Adolfo

Please see the diagnostics for a blower that keeps running when it shouldn't in this article

FURNACE FAN WONT STOP at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

On 2017-08-10 by Adolfo

Why the blower still running if the ac it's off

On 2017-07-09 by (mod) - Air handler fan starts then stops a few seconds later

I would check for these things in this order:

an obstruction blocking the fan,

an overheating fan motor,

a loose or corroded wire connection,

a loose or faulty blower door switch,

a bad control board relay, or a bad start/run capacitor

and if none of those seem to be the obvious problem that I would look at the additional Diagnostics in this article

inspectapedia.com/heat/Fan_Limit_Switch_Test_Procedure.php#FanNoStart

Sorry I can't pin it down more narrowly but I just don't know enough about your situation

On 2017-07-09 by Darin

Air handler fan starts then stops a few seconds later while the rest of ac system continues to run

On 2017-07-09 by (mod) re: blower fan starts, runs briefly, stops

I would check for these things in this order:

1. an obstruction blocking the fan,
2. an overheating fan motor,
3. a loose or corroded wire connection,
4. a loose or faulty blower door switch,
5. a bad control board relay, or a bad start/run capacitor

and if none of those seem to be the obvious problem that I would look at the additional Diagnostics in this article

FURNACE FAN WONT START

Sorry I can't pin it down more narrowly but I just don't know enough about your situation

On 2017-07-09 by Darin

Air handler fan starts then stops a few seconds later while the rest of ac system continues to run

On 2017-07-06 by (mod) problem with fan blades rubbing the case

Rubbing the case is a problem. Perhaps the blades are bent or a bearing is worn or the fan mounts loose or improper.

On 2017-07-05 by Dale

During a rotation, the blades are rubbing the case in one location.

I don't see anything obvious but the fan (blades) does not rotate freely. It stops or gets jammed but I can't see that it is hitting anything.

On 2017-07-05 by (mod) re: noises from the AC/Furnace sounds like a jackhammer

Smart to turn off the power - before a fire got started.

Could be simply a loose component in the blower compartment or a jammed pulley or fan belt. Take a look in the blower compartment for something visually obvious and let me know what you see.

On 2017-07-05 by Dale

When our ac is running, the blower on our ac/furnace unit has started to make a lot of noise (sounds like a jackhammer) along with a burning rubber smell. I cut power to the unit and now would like to understand what has happened so I can repair it or probably get it repaired.

On 2017-07-04 by (mod) re: will removing the air filter damage the blower fan?

Ellen:

sorry your post was temporarily blocked by punctuation that our spam filter thought was a URL

Removing an air filter itself wouldn't damage the blower fan,

BUT if the filter was in the blower compartment and you had to open a compartment door to remove the filter, then a safety door interlock switch could be open - thinking the door is not fully shut - keeping the fan off for safety. ,

Check that out and let me know what you find.

Watch out: running an HVAC system with no air filter will cause dust and dirt clogging of the blower fan itself and may harm other components.

On 2017-07-04 by Ellen M Ames

My blower fan will not start. Really need to know if by any chance it may have to do with the fact that we removed the filter because it was dirty and we didn't have a new one to put in right away and that's when the unit stopped! Can something happen to make it stop due to no filter?

Please help. Trying to fix it ourselves.we were going to replace the motor in the fan unit of the a or handler. It won't start. Very nervous because it's July4th in South Carolina!!

On 2017-06-30 by (mod) re: can I use my furnace blower fan for an AC system?

Yes, Anon, that's a common retrofit situation: an existing forced air heating system gets a cooling coil added above the supply plenum to add A/C to the existing system.

The blower speed may need to change when cooling so if your blower is a 1-speed unit you may need to change the motor and controls.

On 2017-06-30 by Anonymous

Can i use a heater blower on a ac

On 2017-06-22 by (Mod) re - fan squirrel cage noise at end of fan on cycle

Mike: I'd look for a worn fan bearing and if the blower is operated by a motor and pulley system, also for a loose pulley or bad pulley bearing

On 2017-06-22 by Mike

A/c in attic makes loud noises at end of cycle. Sounds like coming from squirrel cage off balance or bearing worn out and wobbles at end of rotation . happens at end of air flow and happens every 3 or 4 minutes. Noise

On 2017-06-15 by Anonymous

Blower motor is d/c it is not running full speed and stops and starts irratically

On 2017-06-09 by steve

I will try disconnecting the wires from the thermostat at the fan side and see what happens tonight. Thanks again for all your input

I replaced the relays, thermostat, and thermostat wire, yet it still runs. That's why this has me stumped. I even swapped out the control board. As far as I know these four things are all that it could be.
I do appreciate all your feedback Dan. Thank you for your advice and help

On 2017-06-08 by (mod) re: diagnose fan that stopped working after a lightning strike

Sounds like a stuck fan relay or shorted wires to the relay; I'd start by disconnecting the wires from the thermostat on the air handler end.

On 2017-06-08 by steve

i don't have any fan limit controls other than the thermostat. I know a lot of heat blowers have a timer or limit controller but as far as I know there is only the thermostat control for mine and even when set in of for heat or cool and auto for fan the fan still runs continuously

I have changed the thermostat and all other mentioned items and cant find anything that suggest another part to check. There is a constant 24v supply to the fan telling it to run.

On 2017-06-07 by (mod)

Steve,

Did you remember to check that there is no manual on switch on the fan limit control itself?

On 2017-06-07 by steve fan stopped working after a lightning strike

i have a carrier split unit 2011year model heat pump. The blower stopped working on the indoor unit after a lightning storm. I replaced the module for the motor which is the x13 model. The module has the capacitor and everything built into it.

After replacing just the module end of the motor the blower came right on and runs perfectly except now it will not shut off unless I open the breaker. The control switch is in auto and the control is in off, yet fan continues to run.

I swapped thermostats with the downstairs unit and still have same problem. I bought new relays and replaced and still have same problem. I then bought new thermostat wiring and still have the problem.

I also swapped out the control board with unit from downstairs and still have the continuous running blower. The outside portion of the unit runs fine and cycles on and off by the temp like it should.
Is there anything else I can look at? ANY help would be greatly appreciated

...

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Or see BLOWER FAN OPERATION & TESTING FAQs-3 - more-recent Q&A about testing the HVAC blower fan.

Or see these

Recommended Articles

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

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BLOWER FAN OPERATION & TESTING FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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