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.

Blower Fan Testing & Diagnostic Q&A-2

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 either a vertical or a horizontal air conditioning unit in many home air conditioning and heating systems.

 

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 A/C with a plastic blower fan. Removed a couple broken blades. Fan turns freely. Thanks for your advice!

Reply: NO - removing fan blades ruins the balance, then the fan bearings, possibly the motor

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.

 

A/C has not put out cool air since the blower unit fan blade was replaced

My husband replaced the fan blade on our AC unit because it was loose and making a lot of noise.

Our air conditioner has not put out cool air since he did this. Is it possible he caused other problems? 2017-09-26 by Wanda

Mod reply:

Wanda

IF there is NO air output then I suspect there is a problem at the fan or blower unit.

But if there is air output of air that is not cool enough, working on the fan itself shouldn't cause that problem - unless by accident hubby left a wire disconnected at a control relay or board.

 

Weak airflow: Better air flow if I install a bigger blower fan?

Anonymous said:
Can I install a larger squirrel fan in my HVAC Unit to increase air flow? 9/11/14 Anonymous

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

AIR FLOW TOO WEAK

A/C runs more and more often and I smell burning

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

Reply:

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.

 

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

Reply:

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

Sparks coming from HVAC blower unit

sparks coming from blower - (July 28, 2014) Anonymous

Reply:

Watch out: Anon"

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

 

Frozen up air handler and refrigerant piping, burned wires,

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. (July 31, 2014) Bill Morse

Reply:

Bill,

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.

Bill 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:

Bill

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

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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-3 - more HVAC air handler blower fan diagnosis and repair questions and answers.

Or see these

Recommended Articles

• AIR HANDLER / BLOWER UNITS - home
• BLOWER FAN OPERATION & TESTING
• BLOWER FAN SQUEAKY NOISE REPAIR
• ELECTRIC MOTOR DIAGNOSTIC GUIDE
• FAN LIMIT SWITCH
• FURNACE FAN WONT START
• FURNACE FAN WONT STOP

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