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 & Diagnostic Q&A#6

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.

On 2019-02-23 by (mod) - air handler turns on and off during a heating cycle

Sounds like it's overheating: check first for a dirty air filter, then for blocked return air.

More detailed diagnostics are at FURNACE FAN CYCLES DURING HEAT https://inspectapedia.com/heat/Furnace_Fan_Cycles_During_Heat.php

On 2019-02-23 1 by Angie

My air handler turns on and off during a heating cycle but if I switch the fan to the on position it stays on but in the auto position it goes on and off until it reaches the correct temp

Question: OK to run the blower if blades are missing from the squirrel cage fan?

Am said:
Is it possible to run a squirrel cage blower fan with some missing blades without damaging the motor? Have a portable ac with a plastic blower fan. Removed a couple broken blades. Fan turns freely. Thanks for your advice!

Reply: no

Am:

I am doubtful. The problem, if there is one, is not so much reduced air output as that if the fan is out of balance it may destroy the fan bearings. Possibly you'll know that a balance problem is occurring by hearing or seeing vibration or wobbling when the fan runs.

Personally, I'd give it a try if it were my unit, but I cannot advise the public to do the crazy stuff I might try.

Am said:
Thanks danjoe. I did try it, what the heck much easier. But sound let me know it was horrendously imbalanced right quick. Oh well.

Reply: AM well at least we know the score. It's time to leave the machine off until the part is replaced.

Question: thumping brick falling noise when AC shuts off on the roof unit

George said:
When AC roof mount shuts off there is a noise like a brick is being dropped on the roof.
Is this normal?
Had a barometric damper on previous house that did not make noise.

Reply:

George:

Look for flexing ductwork or for a loose blower or component in the air handler.

If the noise is coming from a relay, compressor motor, fan motor, or other electrical component, shut off the system while waiting for repair.

On 2017-10-23 by (mod) - blower motor in ac air handler won't turn on

Jan

at FAN, AIR HANDLER BLOWER UNIT inspectapedia.com/aircond/HVAC_Blower_Fan.php we give diagnostic steps to check when the air handler blower won't run. Try that and let me know what questions remain.

If your air handle is for BOTH heating and cooling, then also

see FURNACE FAN WONT START

On 2017-10-23 1 by Jan - blower motor in A/C air handler won't turn on

The blower motor in ac air handler won't turn on

On 2017-09-28 by (mod) - air handler struggling when turns off

Dave,

What you describe could be caused by any of a number of problems, more than I can accurately guess with so little information. Your service tech will probably consider a start capacitor for a motor that's having trouble starting or a bad controller relay

On 2017-09-28 by Dave

My air handler turns off but sounds as if it is struggling. The air flow isn't consistent. It is a Carrier installed in 2010.
Thanks,
Dave

On 2017-08-15 by Leaking water

The air handler is in the attic and is dripping water on top of the ceiling of house. My problem is trying to find the drip. Any suggestion where to look? I cannot find the drip.
Thx,
Darin

On 2017-07-01 by Kenneth Wood

Very great information thanks

On 2017-06-22 by (mod) - blower turns off when doors are closed but on when doors are open - overheats

If by "door" you mean the blower compartment door then perhaps a faulty door safety Interlock switch.

If by "door" you mean doors to the room where the air conditioner air handler / blower unit is located, it sounds as if a motor is overheating.

On 2017-06-21 by Vusi

What cause a fresh air unit aircon to cut off when the doors are closed but switches on again when the door is wide open but after sometime it overheats.this is very confusing because there are no limit switches or sensors on the doors becauce i would suspecr maybe they might be faulty

 

On 2013-03-19 by bill

I put the thermostat in the cool mode and the condensor comes on but the air handler does not turn on...when I switch to heat mode and make it call for heat the air handler does turn on

On 2013-03-19 by (mod) -

Sounds as if the thermostat is not switched over to COOL mode, or if it is, then a contactor or switch in the A/C unit may not be working.

On 2013-03-19 by bill

When thermostat calls for heat the fan comes on...when in the cool mode and calls for air conditioning the fan does not come on

On 2013-03-05 by CK

Our a/c company which maintains our a/c twice a year said the inside of our air handler cabinet is full of mold and we need to have 2 UV lights (brand name Nature's Home) placed inside the cabinet.

The a/c is a Maytag with a 12 year full warrantee. It is about 5 years old. The guy said that mold is not covered, of course.

Does this make sense that there would be all this mold (he said it was a lot) and there be no malfunction of the a/c air handler?

And the UV lights will be $1100 each. They are buying back our old UV lights that they put outside the air handler- which now they say 5 years later was not a helpful idea. The total will be $1600 for this. Can I get your opinion on this?

On 2013-01-29 by cory

I have a nor Dan air handler systemthe motor for the fan is a 240 I'm only getting 120 at the motor the motor was bad I replaced it I can't get 120 off the second black leg on the 3 speed settings the only other way 120 come the end off the second leg is in cool mode all the white wireand they both can t run sound will say ni Isley

On 2013-01-29 by Anonymous

my air handler heat element comes on then it shut off and click but the fan dont run

On 2012-12-17 by (mod) -

Pamela,

Smoking smelling - you should TURN OFF THE SYSTEM IMMEDIATELY and call your heating service tech. The system may be dangerous, or it may just need cleaning and adjustment.

On 2012-12-16 by pamela

our unit was running but was smokey smelling and like something was burning smell in the house. We have had the heat for a month so it isnt because we just turned on. HELP!

 

Question: install a bigger blower fan?

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

Reply:

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

inspectapedia.com/aircond/Weak_Air_Flow.php

Question: weak air flow or no air flow

Rick said:
Blower motor is running but air is barely coming through vents...any suggestions?

Betsy said:
The fan is turning, but the air is NOT coming out!

Reply:

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

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?

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.

Reply:

Jerry, see CAPACITORS for HARD STARTING MOTORS

Anon: see the diagnostics at COMPRESSOR / CONDENSER REPAIR

Question: thermostat troubles

Anonymous said:
when I turn the thermostat to auto it will not come on but will work when you switched to on

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.

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?

Reply:

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

Tony,

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

Question: buzzing furnace blower runs intermittently

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?

Reply:

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 inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions.php

Question: blower air handler fan does not run

bobby said:
air handler fan doesn't come on all the time

Reply:

Bobby,

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.

...

Continue reading at BLOWER FAN OPERATION & TESTING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see BLOWER FAN OPERATION & TESTING FAQs-5 - more-recent questions about why the blower fan won't start, won't stop, squeaks, roars, rattles, or is weak

Or see these

Recommended Articles

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

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BLOWER FAN OPERATION & TESTING FAQs-6 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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