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 or Air Conditioner / Heat Pump 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.

 

I can't find the fan limit switch on my air handler.

I cannot find the fan limit switch.

The plenum is above the blower and does not have an access panel. I assume it would be located in a position to gain access.

My air handling unit has the blower motor and control board/transformer above the evaporator and the plenum is above that level. On 2017-05-11 by Dan C

by (mod)

See our article series FAN LIMIT SWITCH to see locations and sppearance

by Dan C

I am very sure this system has no fan limit switch. The schematic does not show a limit switch.

The fan connects directly into the control board. I believe it is controlled by a P&B relay on the control board. The system will work properly most of the time after power down. I have also removed the G wire from the thermostat at the control board and it continues to run.

by (mod) diagnosing an air handler that does not use a fan limit switch

Dan C:

Air Handlers that use a gas or oil fired heat source would use a fan limit control switch.

An Electric heating system used as backup for heat pump would not require that control.

If that's your situation then I suspect there is a corroded electrical connection or a bad control board or relay in your air handler.

 

 

Can I turn off our attic air handler fan and still have air conditioning?

My fan in the attic runs continuously as it is for the heat. If I turn the breaker to off will it hurt the AC unit? On 2016-03-28 by Anonymous

by (mod) - probably not

If your same attic blower assembly is used for cooling, distributing cool air to the building interior, the A/C won't work with the blower turned off.

And if you called for cooling, it's possible that the cooling coil in the air handler would quickly ice-up as no air would move across it.

 

Can't run blower fan continuously without air the A/C cooling system running too

I recently had my blower motor replaced and my AC is working great but now when I just want to turn on my fan to circulate air, it blows ice cold AC air.

Did wires get crossed on my furnace contol board? Any suggestions on a fix? On 2015-09-23 by Pjespo

by (mod)

The thermostat's FAN ON switch should only turn on the fan so long as the thermostat temperature setting (in cooling mode) is above the room temperature.

If that's not happening I suspect a wiring or control board or relay defect.

 

Air flow pulsates at the supply registers: why?

Air movement speed from grilles is not stable-pulsation. What is possible reason? 2015-09-14 by Garri

by (mod)

Garri

First take a look at the blower fan operation for

- voltage variation

- loose wiring

- a defective control that is cycling the fan on and off intermittently

- loose belt on a belt driven fan

- loose pulley on a belt driven fan

- failing blower motor or blower assembly bearing

 

Thank you to our readers for their generous comments

LS 3845 said: it was a good read i can use the tips every day (Apr 28, 2011)

...

...

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-2, more diagnostic questions & 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

Suggested citation for this web page

BLOWER FAN OPERATION & TESTING 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

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Or

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.

---

 

IF above you see "Comment Form is loading comments..." then COMMENT BOX - countable.ca / bawkbox.com IS NOT WORKING.

In any case you are welcome to send an email directly to us at InspectApedia.com at editor@inspectApedia.com

We'll reply to you directly. Please help us help you by noting, in your email, the URL of the InspectApedia page where you wanted to comment.

Citations & References

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

---

ADVERTISEMENT

---