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 Rotation Direction FAQs

The questions and answers about the spin direction of the indoor air handler blower fan 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.

If the blower fan is mounted backwards the blades are curved the wrong way and you'll see almost no airflow out of the unit.

If the blower fan motor itself is mis-wired or has been damaged or has a bad start capacitor, the motor may run backwards, also delivering very weak airflow into the building.

The questions and answers here pertain to the indoor air handler or indoor wall-mounted blower fan that delivers cool or heated air to the building occupants.

Separately, details about diagnosing and fixing the outdoor unit condenser fan that was running backwards are discussed in our companion article on compressor/condenser units, at CONDENSER FAN RUNS BACKWARDS FAQs

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Air Handler Blower Unit Fan Runs Backwards FAQs

How can you tell if the blower fan is running in reverse?

How do you tell if your fan is in "reverse" mode in a beach box on the Island, OBX On 2017-12-17 by Thomas

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.

 

Why is Air flowing backwards in our duct system?

Filter replaced blower motor replaced sucking air not blowing air? - On 2020-09-06 by Kathy

Reply by (mod) - fan is backwards

I suspect that either the motor was mis-wired or the fan was installed backwards.

New blower fan is now drawing air in instead of blowing air out of our ductwork

Just replaced blower fan now it’s sucking air in instead of blowing it out? - On 2020-09-06 by Kathy

Reply by (mod) - look out for blower fan installed backwards or wired to run in wrong direction

I suspect that we have one of these possible mistakes, Kathy:

1. Wiring error: Most likely: the fan is mis-wired and its driving motor is actually running backwards

2. Wrong fan motor: The wrong motor was purchased and even wired-correctly, spins in the wrong direction for your air handler. The good news is that many electric motors can be made to reverse direction by a simple wiring change.

3. Fan itself is backwards: The squirrell cage fan itself could have been installed backwards - it's an easy mistake and the result is it'll move almost no air. If the fan blades are facing the wrong way air flow will be weak and could reverse direction

 

Our Carrier air handler blower motor runs backwards

1986 carrier blower motor wants to spin in wrong direction On 2016-12-08 by Rob

by (mod) re: blower fan runs in wrong direction

Rob:

Yep that happens, usually after electrical component damage.

See ELECTRIC MOTOR RUN DIRECTION for details.

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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 CONDENSER FAN RUNS BACKWARDS FAQs for Q&A about the spin direction of the outdoor compressor/condenser unit fan.

Or see these

Recommended Articles

• AIR HANDLER / BLOWER UNITS - home
• BLOWER FAN OPERATION & TESTING
• CAPACITORS for HARD STARTING MOTORS
• CONDENSER FAN RUNS BACKWARDS FAQs
• ELECTRIC MOTOR DIAGNOSTIC GUIDE - home
• FAN NOISES HVAC

Suggested citation for this web page

AIR HANDLER / BLOWER FAN RUNS BACKWARDS FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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