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 blower won't run, blows fuse and fan limit switch makes a "POP" sound

Our furnace stopped running due to a blown fuse, but when we shut everything off and put in a new fuse then turn it back on, the fuse blows and we hear a pop sound from the fan/limit switch. What would cause that? On 2018-08-14 by Diane

by (mod) -

You are describing an electrical problem: a short circuit - wires crossed or a motor that is seized.

Watch out: LEAVE POWER OFF so as to avoid getting shocked or starting a fire.

Your repair person will trace the circuit, probably un-plugging components until she finds the failed wire, control, or motor.

Burner continues operate and the blower fan does NOT turn on (UNSAFE!)

The problem I’m having with my Honeywell Fan Limit Control is; when the thermostat calls for heat, the oil furnace burner turns on as it should – however the burner continues operate and the blower fan does NOT turn on.

The burner continues to run until the plenum temperature reaches High Limit setting of the fan limit control – at which point the furnace burner is shut off.

As the plenum temperature cools down the fan will start to run and continue to run until the low set point is reached, if the thermostat temperature is not satisfied – the burner will come back on and 90% of the time the fan will operate as it should;

however if the plenum cools all the way down and a totally new heating cycle is called for, the problem repeats.

This problem occurred with my old (20 years) Honeywell fan limit control – so I replaced the control with a new Honeywell Fan Limit Control.

The problem repeated itself with the new control. I rechecked the wiring and that was correct.

The bimetal probe is the same recommended length as the old one and does not seem to be binding. I did not change the factory setting on the control dial.

I returned the Honeywell Fan Limit Control and replaced it with a second Honeywell Fan Limit Control.

Everything worked fine for the first several cycles and then the problem repeated itself. I have a 10 year old Honeywell 7 day programmable thermostat and have made sure it has fresh batteries and it cycles off and on as it should.

As usual new filters have been placed in the furnace, the furnace has been cleaned and the blower motor seems to function as it should when I set it to manual operation with the switch on the control.

Any ideas? Thanks, Dennis On 2012-09-26

Reply by (Mod) - Daniel Friedman: turn off the system immediately

Watch out: if your burner really stays on and the fan never turns on your furnace may have already been seriously damaged and would be unsafe.

Overheating a furnace heat exchanger can cause cracks that leak fatal carbon monoxide gas into the occupied space. If that's your situation, leave the heater OFF.

Be sure you have working Carbon Monoxide and Smoke detectors.

I suspect you've either damaged the control or there's a wiring error.

These three articles have a rather complete set of diagnostic steps and repair tips. Please see

• FAN LIMIT SWITCH TROUBLESHOOTING
• FAN RUNS ONLY ON FAN-ON / MAN
• FAN WONT START

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 -

Reply 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 -

Reply 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

Blower fan won't recirculate air, but WILL on heat mode

I have new home with a Carrier Weathermaker (58SXA100-JG)...
When I moved in recently I turned my thermostat to cool mode (although we dont have central air yet) and the furnace began circulating air throughout the house nicely.

I noticed the other day that it had stopped, and found that it would not turn on no matter what I did. Switching to winter mode and turning the heat up, it fires up and the fan blows nicely throughout the house.

Doing a little bit of due diligence, I found out that if I disconnect one of the wires from the limit switch, the fan/blower will turn on. So I know it runs.

Upon further investigation, I found a small mouse had gotten into the circuit board and got fried...

The circuit board only has a slight discoloration but I'm wondering if this might be the reason for the blower to work on heat mode, but not on 'cool' mode. I bought a basic Honeywell thermostat that I'm going to try tonight but feel like that likely wont be the problem.

Any thoughts? On 2016-08-24 by Blower fan

by (mod) - When a blower fan runs in one mode (heat) but not in another (cooling) - bad wiring or bad fan control switch

When a blower fan runs in one mode (heat) but not in another (cooling) I suspect either a wiring error or a failed control board or relay. Your mouse sounds like someone to blame in this case, and I suspect you need to replace the control board.

by Thanks!

Thanks. Just ordered a new control board. I'll let you know next week if it worked!

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

Where to start checking if the furnace runs but fan doesn't come on

I installed a new ICM 281 for a Carrier Day and Night FAU. When I turn on the power, the blower fan started running for 1-2 minutes, the hot surface igniter light up red hot, the burners ignited while the blower kept running. Everything seemed to work fine.

A few days later, the FAU stopped working.

Shouldn't the surface igniter becomes red hot first, then the burners light and run for a few minutes, before the blower starts running to push the hot air up into the unit?

What should I test to see why the FAU stopped working?

Thanks. J. On 2019-01-19 by Joe T.

by (mod) - quick checks when the blower fan won't start

Joe

The fan comes on after the plenum is warmed. Not before - on a heating application.

Otherwise the unit would blow cold air on occupants.

Where to start: Watch the fan limit control to see if it's rotating to the FAN ON position.

If the burner runs the heat exchanger temperature should increase and the fan limit control should turn on the fan when the temperature reaches the FAN-ON setting.

If the temperature makes it to FAN-ON and the limit swich calls for the blower to run, then if the blower ran won't start there's a problem with the

- limit switch or its wiring

- the blower fan power or wiring or relay

- the blower fan motor or if it uses a belt, the drive belt

See our detailed troubleshooting and repair procedure

at BLOWER FAN WONT START

If your fan limit control switch does not seem to be working properly, see FAN LIMIT SWITCH TROUBLESHOOTING

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.

Old GE forced air furnace fan limit switch replaced but fan still won't turn on

I have an old GE forced air furnace(40yrs old)and had to replace the fan/limit control Honeywell M#L4064B.

The reason for replacing the control is because the fan would not run when reaching the fan on set point. The fan does run manually.

The problem still exists after replacing the fan control.

At this point, because of the age of the furnace, I'm finding it near impossible to locate a schematic for this heater.

Any ideas as to why the fan does not start when called for?

When the burner reaches the high limit the gas valve does close. On 2016-12-05 by Bill -

by (mod)

Bill

If the fan will run manually we figure that the fan motor and blower assembly are OK, so what remains is a fan limit control that's not turning on the fan when the plenum temperature reaches the FAN-ON setting.

And since your fan limit switch is a new one, I don't suspect the control itself. So more likely the problem is with the blower assembly.

If you haven't already done so, you should confirm that by watching the rotating dial on the fan limit switch.

At least the high limit is working - to avoid destroying the furnace heat exchanger or killing the building occupants.

See the diagnosis and repair steps at BLOWER FAN WONT START

Also take a look at this article FAN LIMIT SWITCH TROUBLESHOOTING to see if that helps.

Unfortunately one can't easily test the switch off of the furnace since you do not want to manually twist its dial - that risks de-calibrating or damaging the switch making it unsafe.

by Bill

I followed the steps for testing the fan/limit control and it appears to work fine and shutting the gas valve off when reaching the high limit setting but when reconnecting the fan motor lead the fan does not turn on.

What other component is related to calling for the fan to run that would be after the fan/limit control. I was thinking the fan relay may be suspect but the fan does run in the manual mode.

by (mod) - watch the fan limit switch dial rotate as the plenum heats up

Just to be sure we're on the same page, you're watching the heater dial rotate as the supply plenum heats-up. You should see the dial rotate until the dial's FAN ON position or temp setting is satisfied.

At that point the fan should run. It won't run until the plenum has heated up. Since you're seeing the furnace limit switch shut the burner off at the HI-OFF position or LIMIT position then we know the plenum temp must have passed the FAN ON position.

There's probably not much besides a fan relay to look at.

by Bill

Thanks for the info. I'll inspect the relay for possible problems.

Furnace blower wont' run, I want to make it run continuously

The motherboard will turn on and run the heat but no blower. Would like to bypass the blower to run constantly. On 2016-12-31 by Warren

by (mod)

Warren, SOME but not all fan limit switches contain a FAN-ON switch that will keep the fan on constantly.

If your limit switch lacks that feature you might be able to install one that has it.

I'd be reluctant to simply hot wire the fan motor directly.

by Warren - successful diagnosis of fan problem - need new control board

Thanks for the feedback.

We have the fan running now but no heat. I will pick up a new board this week and replace it.

Honeywell fan limit switch fails to turn on the blower fan

My furnace's Honeywell fan limit switch fails to turn on the blower fan, but it does shut off the burner when it reaches 200F. When the dial rotates to the lower limit, fan control wiring side (left) isn't closing (tested with multimeter). FYI, the blower fan works well when AC is running.

Is it possible to make the left side connection close when the dial reaches lower limit to turn on the blower fan? If so, how to repair it? BTW, there's no manual fan ON/AUTO control button on the switch. Thanks, On 2023-11-28 by Bob R.

by InspectApedia Publisher - repairing the internal parts on that fan limit control risks making it unsafe

@Bob R.,

I'm sorry to say that I think the control needs to be replaced.

Watch out: The worry is that any effort to repair the internal parts on that fan limit control risk making it unsafe.

For emergency heat and where the limit switch had no manual fan-on switch, you may be able to turn the blower fan on continuously at the thermostat or by direct wiring.

Take care to avoid a shock.

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.

It 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.

Nordyne Furnace 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.

My furnace comes on but the blower fan does not run

Furnace burner comes on but fan doesn't. Not sure if it's fan switch or capacitor or fan motor.

The fan limit switch does turn when it heats up. It has 4 leads, 2 fan and 2 limit. Can I jumper the 2 leads for fan to see if the fan runs? (Nov 5, 2014) John M.

Reply:

John

I would first

- turn power off to the unit, then see if the fan assembly will rotate freely

Then observe: your heating service tech will probably check for voltage at the fan motor - if there is none we think it's a control problem. If there is voltage and the motor hums but doesn't spin it's more likely a start/run capacitor problem.

See FURNACE or A/C BLOWER FAN WONT START

Fan limit switch hums but fan won't start

You stand next to the switch and fan not running and you can hear the switch hum lesterstocker@yahoo.com (Jan 1, 2016) les

Reply:

I can only guess from my remote position, but a humming switch that doesn't actually operate suggests instead: a seized electric motor, bearing, pulley, blower assembly, OR a failed switch / relay. I would turn the system off and call a repair person.

Aux gas heat ignites but fan doesn't come on

My furnace works fine when set on the heat pump. When it switches to the gas auxilary the gas ignites, but the fan doesn't come on until the high heat turns off the gas.

Then the blower comes on and runs until the air starts cooling. The AC guy was here and thinks it is the control board. but I want to make sure.

We had a problem with a clogged condensation pipe last year, but there doesn't seem to be any water issues this time. (Nov 25, 2014) Jane Metzger

Reply:

Jane

In heat pump mode heat is coming from your heat pump and the coil in the air handler - on the gas furnace the fan limit switch is probably not being called on to do a thing - since its job is solely to protect the heat exchanger in the gas fired furnace.

But when the system switches to aux heat then the gas furnace wants to operate (or you want it to) and the fan limit switch is on-duty.

I'm not smarter than your on-site AC guy but you'd think that if the control board in the heat pump is turning on the gas furnace - that is the gas furnace tries to run and its burner ignites, then at that point it's the fan limit switch that actually turns on and off the blower (in response to furnace heat exchanger temperature).

I'm not quite clear on what's happening but can offer a diagnostic question or two.

What is turning off the gas: the fan limit switch?

On most gas furnaces the blower will run continually during a call for heat and will run for a short time after the thermostat is satisfied - to cool down the furnace heat exchanger (avoiding damage to it).

The limit switch will shut down the burner if its sensor thinks that the heat exchanger temperature is dangerously high.

I'd start by checking that the wall thermostat switches are all set properly.

I'd continue by watching the fan limit switch during a heating cycle to see if its dial rotates and noting its position when the burner operates, burner stops, fan comes on or off. (the limit switch dial should start moving until the burner has begun heating the plenum)

See FURNACE or A/C BLOWER FAN WONT STRT

Lennox blower fan won't run, Furnace flashing indicator says limit control is bad; replaced unit still flashes.

My furnace (lennox) has stopped working it is flashing that the limit control is bad. I replaced it and is still flashing that i is bad and my blower is not engaging or spinning but it sounds like there is electricity going to it. I replaced the blower a few months ago. What do I do next? (Nov 9, 2015) stephen

Reply:

When you replaced the blower I am guessing that means the fan motor or motor + actual blower assembly.

If the blower isn't running either the motor or a control is bad or worse, an underlying problem - maybe a short or nicked wire - damaged the new motor or its start/capacitor.

I'd start by checking the things that I've missed before like: be sure that the blower door is not open or ajar or that the door switch isn't shutting off the blower.

Can a failed outdoor compressor/condenser cause the indoor blower fan not to start?

I have a Carrier model 38YZA heat pump outside unit with a Carrier model FV4 inside unit in the attic for the upstairs level of my home in Huntsville Al.. Yesterday I noticed the upstairs temperature was well above the set temperature of 72 degrees.

I did not hear the inside blower motor running and went outside to check on the a/c unit. It too was not running but I saw ice on the refrigerant line leading to the house. I turned off the system at he thermostat immediately and left it to access later in the evening when it became cooler.

Later in the evening I checked to verify the circuit breakers were in the on position which they were. I switched the system on again at the thermostat but nothing started, no inside blower (even when switched from auto to blower), nor the outside fan or compressor - all silent.

My question is can a failed "outside" compressor capacitor cause silence at the outside unit fan and compressor as well as the inside fan motor to not start? When I turn the system on at the thermostat, I hear a slight click within a few seconds as if the thermostat is calling for the rest of the system to turn on. On 2017-08-23 by Tom b -

Reply by (mod) - Yes in some conditions

Yes, maybe, Tom. For example, in heating mode, the blower fan won't start below a certain temperature.

That feature avoids blowing cold air on people during the heating season.

That circumstance could occur IF your outdoor compressor/condenser unit is a heat pump and is operating in heating mode.

But in cooling mode, if the outdoor compressor/condenser isn't working, in a typical residential air conditioning system, the blower will run, but the air delivered simply won't be cooled.

Carrier heat pump with electric heat. The blower fan will not run with the heat pump

I have a Carrier heat pump with electric heat. The blower fan will not run with the heat pump, but will run with the electric heat. Any suggestions? (June 16, 2014) Lee Ann

Reply:

Lee Ann that sounds like a control or control board problem, as you know that the blower itself will operate.

A possibility to check first is that the heat pump is actually working.

If we are trying to heat a space and if the heat pump is unable to raise temperatures inside the air handler to a sufficient level, a fan limit switch might keep the blower from ever turning on - as it doesn't want to blow chilly air on people who are clamouring for heat.

Heat pump works but back-up gas furnace does not work properly

My furnace works fine when set on the heat pump. When it switches to the gas auxilary the gas ignites, but the fan doesn't come on until the high heat turns off the gas. Then the blower comes on and runs until the air starts cooling.

The AC guy was here and thinks it is the control board. but I want to make sure. We had a problem with a clogged condensation pipe last year, but there doesn't seem to be any water issues this time. 11/25/2014 Jane Metzger

Reply:

Jane

In heat pump mode heat is coming from your heat pump and the coil in the air handler - on the gas furnace the fan limit switch is probably not being called on to do a thing - since its job is solely to protect the heat exchanger in the gas fired furnace.

But when the system switches to aux heat then the gas furnace wants to operate (or you want it to) and the fan limit switch is on-duty.

I'm not smarter than your on-site AC guy but you'd think that if the control board in the heat pump is turning on the gas furnace - that is the gas furnace tries to run and its burner ignites, then at that point it's the fan limit switch that actually turns on and off the blower (in response to furnace heat exchanger temperature).

I'm not quite clear on what's happening but can offer a diagnostic question or two.

What is turning off the gas: the fan limit switch?

On most gas furnaces the blower will run continually during a call for heat and will run for a short time after the thermostat is satisfied - to cool down the furnace heat exchanger (avoiding damage to it).

The limit switch will shut down the burner if its sensor thinks that the heat exchanger temperature is dangerously high.

I'd start by checking that the wall thermostat switches are all set properly.

I'd continue by watching the fan limit switch during a heating cycle to see if its dial rotates and noting its position when the burner operates, burner stops, fan comes on or off. (the limit switch dial should start moving until the burner has begun heating the plenum)

Blower Fan Won't Start / Won't Run if Burner Won't Run FAQs

Furnace fan does not run on call for heat

I'm testing my furnace in anticipation of the snow season. The furnace is 8 years old. I can get the fan to kick on, but only on the fan option and not when I switch it over to heat. I have checked the wiring, changed the filters and still no luck.

I'm thinking it is possibly the fan relay switch or I need to replace the thermostat??? I installed a new thermostat, but have the same results. Looking at the control board, all it is showing is a solid green light. Your thoughts.

...

I got the pilot light to engage. It ran for about 30 seconds then shut off. I haven't gotten it to kick on since then. (Oct 4, 2014) Will

Reply:

Will if the gas pilot won't stay on your system may need a new thermocouple.

 

Furnace blower fan cycled off too quickly: gas valve was partly closed!

Just lit the furnace, and it was cycling the blower off in less than a minute.

After reading the article FAN LIMIT CONTROL SETTINGS, I pulled the cover off to watch the limit switches. They were set right on.

What I found was, that I hadn't turned the gas full on, so after the blower kicked in, the switch was cooling down to the shutoff. A little more gas kept the the dial where it was running. - On 2012-10-07 by Warren

Reply by (mod) -

Warren,
Thank you for the helpful short on cycle diagnostic comment. I will add it to the article text.