HVAC blower fan testing & diagnosis FAQs set #3

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.

HVAC Blower Fan Testing & Diagnostic FAQs3

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 2019-07-17 by (mod) -

Sounds odd to me too; One wonders why the fan would know to slow down at night. CHeck the manual for the unit to see if there are control board switches that might vary the fan speed based on temp or other conditions.

Other possibilities:
- overhreating equipment
- a failing relay or control board that is responding to ambient temperature

On 2019-07-17 by Joe

Forced Air Unit with Central A/C ( with Heat Pump) added about 1 1/2 ago. So this season the A/C blows cold all day and works fine until the late evening when the out side compressor stays on, but only a trickle of cold air comes through the vents. Is my blower motor the culprit ?

When I turn A/C on the next day ( after turning it off in the middle of the night) the A/C runs fine again until evening.

On 2019-05-28 by Sean

I have a lennox air handler in the attic, serial number# 583E 501 29, it has a serious vibration that seems to come from the blower wheel, I took the blower wheel off and it feels like the blade are a little loose were they are tack welded on the frame,

also its one unit but 2 seprate thermostats both were set to off because the fan blower/air handler would go off even after an hour so I had to turn off the single pole switch to power down the unit, so I believe I have 2 problems here, any ideas on what they may be, Thanks Sean

On 2019-02-22 by Emilio

American Standard has a wheel fan that is connected to a plastic container that blows the air in duct. The wheel fan gets disconnected from the core. When the motor starts, the wheel fan goes berserk inside the plastic container box and will shut down because air won’t release and this patient is no good. There is a defect from the wheel fan and the motor that the fan continues to spin and fan stays put. Not good

On 2019-02-19 by (mod) - Repeated failures of Trane blower motor

I agree with you that the behavior sounds abnormal. There might be something in the local environment such as unusual moisture or even corrosive gases, or low voltage, or some other installation issue that could be a factor.

Certainly plenty of blower motors run in daily use for decades. Let's both do some research on electric motor failure rates as a function of climate such as Florida.

See ELECTRIC MOTOR LIFE

On 2019-02-19 by Moshe

I had a 3 ton Trane Package unit installed less than 3 years ago from a reputable company in Miami, FL. In less than 3 years, my blower motor had to be replaced twice. To me, that sounds crazy and like something is just not right either with the unit or the install

. Company says its due to humidity / environmental conditions etc. I live in Miami my whole life, never remember any other AC units needing a new blower motor yearly. Is this normal behavior for a practically new AC?

On 2018-11-09 y (mod) -

JOsh

Look VERY closely at the squirrel cage fan blades - even a modes amount of dirt there can cut air flow significantly.

Then have your service tech check the fan speed (and motor and voltage).

I don't assume the blower or fan is under-sized unless the problem has been present since original new installation of both the blower and the ductwork.

For detailed diagnostic help see AIR FLOW TOO WEAK https://inspectapedia.com/aircond/Weak_Air_Flow.php

On 2018-11-09 by Josh

I have a gm gas furnace from around 78. My problem is I don’t have much air flow coming from the registers. Blower isn’t dirty, used a leaf blower on it. Air filter is clean.

The blower does rattle which I have fixed by using a 2 by 4 and old rag to support squirrel cage. Registers are hot to touch, registers closer to furnace gmhave a bit more air flow but not much. The furnace has 1/3 hp blower motor. It’s for 1900 sq ft house.

Is it undersized? A couple of years ago I replaced my swamp cooler it has 1 hp motor. Why would the furnace only use a 1/3?

On 2018-10-22 by (mod) - A backwards running blower motor

Scoot,

if we assume that your ductwork is connected correctly then either your blower is installed backwards which can happen during cleaning or assembly, or the motor is running backwards. If a blower motor is running backwards the squirrel cage fan won't move as much air as normal but it will move some.

A backwards running blower motor can be caused by incorrect dip switch settings, incorrect wiring, or even a power surge or lightning strike. Also if you search this website for


electric motor runs backwards

you will find more details

On 2018-10-22 by Scooter

Blower motor blows air out the return vent and sucks the air in though registers. What's the problem? It's a NEW package unit.

On 2018-07-13 by (mod) - clicking noise every 2 seconds

David,

The blinking light that you describe is almost certainly a diagnostic but I don't know what the specific light means for your system. To decode a signal light one needs the brand and model of the equipment and with that information one obtains the service manual for the equipment.

The back of that manual will have a page or two listing the different blinking light signals and getting their meaning and telling you what needs to be done.

For example a blinking light might indicate that an air filter needs to be changed.

On 2018-07-13 by david waite

My central air is working but there is a clicking noise every 2 seconds and as I opened the door to inspect, I noticed a green led light blinking simultaneously with each click. Can you help? Is there a problem?

On 2018-07-09 by Mark

My supply fan blower starts and then immediately goes into fault. What could be the problem?

...

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

Or see BLOWER FAN OPERATION & TESTING FAQs-4 - 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-3 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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