HVAC Air Handler Blower Fan Won't Start FAQs

Q&A on Why the A/C or Heating Indoor Air Handler Fan Will Not Run

Air Handler Blower Runs but Air Is Not Delivered FAQs

Indoor air handler fan runs but no cool air comes out of supply registers

Maybe you can give me a little direction.

My 'a/c wasn't working, turned fan to "on", no air from vents.

Opened handler cover. Coils were cold/iced. I defrosted and cleaned with coil cleaning foam. Checked and cleaned drain line and dried the sensor. Still no air out of vents.

If I turn off unit at the switch. Then turn it back on, I can hear the thermostat click, and the a/c unit 'picks'.

Then the internal fins in the blower are moving. I hear a kind of whump ... whump ... whump like some motor is trying to engage but nothing is happening.

Even thought the fan inside the unit is spinning, no air blowing from the vents.

Is it time to go outside and work on the compressor part or could it still be something inside at the handler?

Its Friday after thanksgiving, trying to fix this myself if its possible, or at least know exactly what the problem is before I call in the "pros".

I have some electronics background and I have changed out the run capacitor ouside a few times. Usually if its that, the air does blow from the vents. On 2020-11-27 by Pamela -

Reply by (mod) - blower fan runs but no air comes out at the supply registers

If the blower runs and no air is delivered,

un-blocking the coil is a good place to start; but in addition to ice the coil could be dust and debris clogged;

Still I'd expect some airflow, just that it'd be weak.

1. Are you sure the blower fan is actually running?

2. Have you made sure the air filter is new and clean? Is the blower itself very dirty so it spins but isn't moving much air?

3. Have you followed the ductwork to be sure that a damper isn't closed and that the ducts are all connected and un-damaged?

4. Is there a broken fan belt between fan motor and fan assembly ?

5. Is the blower fan mounted backwards?

Heater Blower Runs but No Air Comes out of Supply Registers

My heater blower is constantly running but no air is coming thru vents - On 2017-03-06 by Cy

by (mod) - is it the motor itself or a broken fan belt

Check first that the blower fan itself is actually spinning. For example, in a belt-driven blower fan unit, the blower motor may be running but if the belt is broken or disconnected the blower fan won't spin and no air is moved.

That sounds like disconnected air ducts. A blocked or dirty filter might slow air but wouldn't normally stop it completely.

Start by checking in the blower compartment - that the fan is working.

Then follow the ductwork to look for an obstruction, disconnection, or a closed duct tamper

Air Handler Blower Motor Electrical Control FAQs

Furnace won't re-start after initially reaching the thermostat set temperature

My oil furnace runs to setting temperature, then stops until it calls click sound for heat again, the furnace try to run but it stops then the light is on. I have to wait for the house temperature goes lower then press the button, its back on again. then it keeps on and off like that.

We did change oil filter, cad cell and nozzle. But its still not working. Please help. Thank you - On 2018-03-13 by May -

by (mod) -

May

Watch out: You need a service call to find out why the system is going off on safety-reset.

Watch out: For safety you really want an onsite service technician - this isn't a proper homeowner repair topic.

DO NOT keep running by pressing the reset button - see PUFFBACKS, OIL BURNER

See the controls and resets found at

• CAD CELL RELAY SWITCH
• COOLING & HEATING CONTROL & SWITCH INDEX - index to all controls
• FIRE SAFETY CONTROLS  for oil burners

Older trane unit indoor unit circuit breaker is stuck in the on postion - indoor unit nothing comes on .

Can the breaker that is stuck in the on postion not let the air handler come on?

I have a older trane unit indoor unit breaker is stuck in the on postion - indoor unit nothing comes on .

have ck all breakers.outdoor unit when contactor is pushed in it comes on On 2019-06-30 by Tom -

Reply by (mod) - does circuit breaker prevent the fan from turning on?

Tom:

From just the comment that you've posted I don't understand the situation except to give you a very serious warning that if you have a circuit breaker that is as you describe it stuck in the on position that's extremely dangerous risking a house fire.

Watch out: a "stuck" circuit breaker is unsafe, risking a building fire. Ask your electrician to replace the bad circuit breaker.

Then ask her to check for a short or electrical failure on the electrical circuit that the breaker is supposed to be protecting.

 

York blower motor does not come on unless I press the contactor (relay switch)

This York blower motor does not come on, the power was verified, if I manually press the contactor in it works , but not on its own , I’m not getting 24 volts to board. On 2020-04-23 by Luis -

Reply by (mod) - York blower motor won't turn on

Luis

Good first diagnostic steps.

If you jump the thermostat terminals the burner should start first; the blower won't come on until the plenum has heated-up.

So: on a call for heat, does the burner ignite? (Is this gas, or oil?)

Also, if there is a manual ON control on the limit control, turn it to FAN ON - if the blower runs then the problem isn't the blower itself.

More diagnostics are in the article BLOWER FAN WONT START.

Blower fan works in heat but not in A/C mode

Blower motor works on heat cycle but won’t when switched on to A/C cycle? Fan motor working outside on unit but not on furnace? I’ve had door on and off turned breaker on and off too. Wiring looks ok capacitor? On 2020-05-26 by Darrell -

Reply by (mod) - blower works only in heating mode

Darrell

If the blower motor works in heating mode I don't think its failure to start in cooling mode would be a blower motor capacitor failure.

More-likely there is a wiring error (if the blower motor has never worked in cooling mode)
or
a control board or relay failure (if the blower motor used to work in cooling mode)

Fan blower runs in heat but not in cool mode

Fan blower not running on A/C but run on heat mode; and also couldn't turn on the fan from the thermostat, need help, please On 2020-09-06 by PETER -

Reply by (mod) - blower fan runs in heat mode but not in cooling mode

Sounds like a wiring problem or a bad control board

Heater fan won't start in AUTO mode but works in MAN-ON position

Heater fan could not automatically start when we turn on the heater and set the fan as Auto, we have to manually turn on the fan when using heater, however, when we turn on A/C, the fan is automatically on and off. On 2020-12-02 by Linda Chen -

by (mod) - blower fan won't start when in A/C mode

Linda

When a forced air fan in an air handler will run properly in cooling mode but not in heating mode AND if you've set your thermostat to HEAT but the fan won't come on then I suspect a problem with the heater's control board.

See details at FAN ON AUTO MAN THERMOSTAT SWITCH

In Heating mode, when the heat pump compressor is on the fan stops.

Just replaced fan in tempstar 10 outdoor AC. Last one was over heating. Now, when the compressor is on the fan stops.

When the compressor stops, the fan turns on. So, what did I do wrong? Gah! On 2018-02-23 by Michael -

by (mod) -

Larry

In heating mode when your heat pump first starts running, the indoor blower fan may be delayed until the A-coil in the air handler reaches sufficient temperature. That's to avoid blowing cold air on perople when in heating mode.

Also, it's normal for a blower to stay on for a minute after the call for heat stops - to cool down the heat exchanger.

Beyond that a blower that stays on is doing so either because of a FAN ON switch setting (not your case) or because there's a problem: an overheated heat exchanger (maybe blocked air flow or dirty air filter) or a bad control board or limit switch.

IF the cycling on continues for many minutes or longer after the furnace has remained off then I suspect a bad control or relay.

OR for some furnace models such as the Norton D-series by Broan, a heat anticipator in your wall thermostat may be set incorrectly.

Note that not all thermostats even have a heat anticipator but some models do.

See HEAT ANTICIPATOR ADJUSTMENT

Air Handler Blower Fan Won't Run: What to Check, FAQs

My furnace blower fan will not engage - the burner starts but not the fan - what steps do I follow to troubleshoot this?

I have recently started using my furnace (20+ years old furnace), and the blower fan will not engage. The pilot and gas burners start, but the fan does not. I have ensured that the fan is set to "auto", on the thermostat.

Is there any procedure I can do to troubleshoot the issue? I have seen several topics, however none seem to be helpful. - J.B. 12/31/2013

Reply:

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. But here are some suggestions to start troubleshooting the problem of a furnace blower fan that does not start:

Step 1: Confirm that electrical power is on to the furnace and that the thermostat is calling for heat (or cooling if in cooling or air conditioning mode)

Step 2: Identify and check other controls that can prevent the blower fan from operating. Some heating or cooling systems may have additional design features that control the blower fan.

Example: a blower compartment door that is not fully closed may leave a blower door safety switch in the OFF position.

Example: a failing control board or motor in the air handler can trip a circuit breaker inside the unit or at the electrical panel.

Example: on a call for heat in a water to air heating system, a zone valve that sends hot water from the heating boiler out through a heating coil in the air handler or blower unit has to first open to let hot water flow and then when the valve is open an end switch turns on the blower fan.

Step 3: Continue by confirming that the blower fan will operate.

Your system probably has a manual FAN ON switch on the thermostat, or if not, there may be a FAN ON push pull switch right on the fan limit switch in the air handler.

If you can make the blower run then we know the problem is not with the blower motor or drive belt or assembly and we'd go to step two.

See  FAN AUTO ON THERMOSTAT SWITCH for the switches on the thermostat;

For a manual FAN ON switch found on some limit switches in the blower or air handler assembly itself

see CONTINUOUS BLOWER FAN OPERATION

Step 4: I would continue diagnosis by watching the behavior of the fan limit switch as the furnace heats up; presuming nobody has messed with the switch to try to change its settings, it should act as described in the article BLOWER FAN WONT START beginning

at FAN LIMIT SWITCH TROUBLESHOOTING

Summarizing:

Watch the dial on the fan limit scontrol witch on a call for heat.

If the fan limit control dial rotates as the plenum heats up (as it should) the dial will rotate past the FAN ON temperature. At that point the blower fan should start.

If the burner is running but the fan limit dial never moves then the problem is in your case probably the limit switch itself.

Step 5: Other things to check

Include the fan motor start/run capacitor and the fan motor itself as well, of course as the blower bearings and movement.

If the air handler blower fan starts and runs in manual FAN ON mode I suspect the limit switch rather than the fan motor or door switches.

Followup by EB -Replacing the circuit board resolved the issue of a fan that wouldn't run

@inspectapedia.com.moderator, replacing the circuit board resolved the issue.

the start capacitor arrived and when replaced did not resolve the issue (circulation fan will still not turn on).

I attempted to check if the fan motor is getting power, but not sure if I am checking correctly...I followed black and white wires from safety switch to the board and was able to verify 120v. I removed the black and white wires from the fan motor to the board and set fan to “on”. I do not get voltage at those locations on the board.

I also checked voltage past the transformer is 24v. I tried jumping R to G at thermostat and fan will not run. Do you have any additional advice?

Since there is not 120v at the location on the board that the fan motor is connected when it should be running, I am going to order a replacement circuit board. Thanks for suggestions so far. I will advise if this resolves the issue.

I ordered the capacitor and will double check wires while I wait. Thanks for the link to DMM use and safety reminders.

Reply by Inspectapedia Com Moderator - After trying everything else, it was the circuit board for the blower fan

@EB, Well done. Glad it's been resolved. And thank you for letting us, and other readers, know the outcome.

The most common problems when the fan won't run and when we do suspect the motor itself or its start capacitor, are a poor connection, bad relay, or on occasion a bad control board.

Do keep us posted. That will help other readers.

Followup by EB - replaced fan motor, spinning the fan doesn't get it started

Thank you for the reply. I could not find a reset button and decided to replace the motor. With a new motor in place, the blower will still not turn on

. I did not replace the start capacitor when I replaced the motor. I don’t have a meter to check if the capacitor was damaged too.

I read that giving the squirrel cage a spin while calling for heat or air could be a test to see if capacitor was bad. Spinning the cage does not seem to work. Could my problem still be a bad capacitor? Or should I be checking something else? I know what caused the issue, just not sure how to fix it. Thanks in advance for any advice.

Reply by inspectapedia.com.moderator (mod) - replace the starting capacitor

@EB,

Possibly; a starting cap is very inexpensive - so often a technician will simply try replacing it.

Be sure your wiring is correct and all connections good;

Be sure there is power to the motor;

Watch out: you can be shocked or killed working on electrical stuff, or get fingers cut off in a spinning fan.

DMMs VOMs SAFE USE OF

may be of help

Then check for a burned or damaged control board.

Bad zone valve on water-to-air heating system kept blower from turning on

I was able to figure out the issue and it turned out to be a zone valve. I am not new to HVAC but also not a professional and haven't messed around this system much.

The unit is inside a bathroom ceiling servicing a hotel room without an access panel so i tried to do as much diagnosing before cutting a hole in the ceiling and installing an access panel to the area of the AHU valves.

In this system the heat zone valve not only open and closes the tempered water but also powers the blower unit.

I am working on diagnosing why my heater wont turn on, the blower motor will run when on cooling but not for heating. I have two boilers running with a boiler pump and know my heat pipe is up to temperature but the fan wont start up. Is there a fan limit switch just for heating? On 2017-11-21 by Thomas -

Reply by (mod) -

Thanks for the follow-up Thomas that will help other readers. I think that you are describing a water-to-air convector unit and a fan that wasn't turning on.

Hard Starting or Humming Blower Fan Motor FAQs

Blower motor hums, won't start

I replaced start capacitor but blower fan will still not start by itself, just hums. I was able to start the fan while humming by pushing squirrel cage with screwdriver. On 2018-06-06 by Steve -

Reply by (mod) - sign of a bad motor capacitor

Humming noises from any electric motor usually point to a failed motor or a bad starting capacitor

Usually the situation you describe is traced to a bad start run capacitor, bad fan bearings, low voltage, or one of the other causes discussed in the article BLOWER FAN WONT START such as a seized motor.

See ELECTRIC MOTOR DIAGNOSTIC GUIDE

and also

see FAN NOISES, HVAC

 

What are the things I can check on my AC unit when the fan motor hums and the blower fan is not coming on?

By private email:

I would appreciate any help or comments on things I can check on my AC unit. The blower fan is not coming on.

There is a 3 amp fuse in the wiring system that I have checked and it is good. Something tripped the breaker on the unit itself. I tripped it off and turned it back on.

The system came back on but there is no forced air coming through the vents and the condenser coils began to freeze up almost immediately. The unit has a squirrel-cage fan and it will not come on. With the breaker in the main panel switched off I reached in and the fan spins freely..

I then switched the main breaker back on and I can hear a “humming” but the fan won’t spin.. is it possible that the start-up capacitor and/or starter relay has gone out?? Again, any help would be greatly appreciated.. will be 90* hear tomorrow and my wife will be here with no air this week if I can’t get it going tomorrow..On 2018-10-14 by anon -

Reply:

"something tripped the breaker on the unit itself"

tells us that there was an over-current or short circuit; that could be a failing motor, low voltage, or a failed or shorted switch, control board, relay, or wire.

A service tech would probably inspect for something visually obvious: damaged, burned, loose, and then follow the current path through the equipment.

Watch out: you could be shocked or killed if you don't know how to follow those procedures safely.

Furnace blower motor hums and fan is not spinning.

I have a G51MP Elite Series Lennox Furnace and HVAC unit. The Blower located in the Furnace is not spinning, just hums, although it spins freely when turned by hand.

When I turn the Fan from "auto" to "on" on the thermostat , and I help the blower by moving it a little by hand, it runs, but only runs slow. I replaced the Blower Start Capacitor, but the same results occur. Any Ideas, what can cause this? On 2020-07-14 by Mark Cohen

Reply by (mod) - signs of a bad fan motor start capacitor

Mark

Whenever we have an electric motor that will run if given a spin or push I think the problem is probably a bad start capacitor

See FAN MOTOR START CAPACITORS which can offer a temporary repair that gets more life out of a failing blower fan motor.

Question: blower fan runs if I give it a spin

We have a Nordyne furnace Model #PGC2TC060D24B. The Blower # is 622636. When we put the fan in run mode, the fan will run sometimes and sometimes not until I spin the wheel. It is doing this when we try to run the furnace and air also.

Where is the capacitor on this motor? It is not on the outside of the motor. Do you think it is the capacitor?

Where is the capacitor located on a #622636 motor on a Nordyne furnace # PGC2TC060D24B furnace It is not on the outside of the motor. The blower will run sometimes when the thermostat is in the run mode and sometimes it will not run until I spin the wheel. 2019/10/25 Dsmith 10

Reply:

I don't know this furnace exact- model, D.S. nor could I find your model number - have you got the IO Manual for it?

If not we can help find one - that'll include wiring diagrams and parts lists.

But yes in general if the motor will run when you give the blower fan a spin then usually the problem is the starting capacitor (if present) OR a bad start relay control switch.

Furnace fan stopped running after intermittnet failures

I have a gas forced air system. Furnace ignites fine. Fan was only engaging when on auto setting every several cycles of furnace firing up.

Became less frequent and now doesn't engage at all. Tried running when fan in an "on" setting.

Worked on several occasions after running fan for a while but no fan no longer kicks back on after furnace fires up.

Additionally, we had a problem late summer where AC did not engage when fan on auto setting but did work when fan on contiuous run setting.

Does this sound like a control board problem? Thanks. On 2020-12-19 by Darryl A -

Reply by (mod) - signs of a failing fan motor or control relay

Darryl

When the fan doesn't start, does the burner shut off at high limit temp? That's a critical safety feature.

If that's going on the problem could be a bad fan motor or control board or relay - or of course something else.

When a blower fan runs in the MAN-ON position at the thermostat or at the fan limit control but doesn't run automatically, we look first to see that the burner is operating properly.

Bottom line: you are probably describing a failing control or failing fan motor.

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