Blower Fan Won't Stop - FAQs

Q&A on a Blower Fan that Will Not Stop

Air Handler Blower Fan Won't Stop Running FAQs

In Heat mode our Furnace will not turn off and keeps blowing out cold air

When the house reaches the desired temperature sometimes the fan keeps blowing even though the burners have stopped and the fan then blows cool air and does not stop.

I have to then turn the heat off and in a few minutes back on and then it runs properly by turning off. The fan is always set to auto. - On 2018-01-15 by Anne

Even took the batteries out of the wall unit and it is still on and blowing out cold air - Christina 2018/01/01

by (mod) -

Anne, and Christina:

On most forced warm air heating systems the fan will run until the call for heat is satisfied at the thermostat, and for a brief period thereafter.

But if the fan never turns off the:

SOME (not all) fan limit switches include a white push-pull knob that forces the fan to run continuously - or leaves it on AUTO.

That's what I suggest you look for first.

Then check the room thermostat FAN settings. Set the fan to AUTO, not to ON.

The indoor air handler blower can be forced to keep running, as we explain at

• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH
  
  That switch and its operation as well as other causes for a fan that won't stop are listed in the diagnostic steps given in the article
• FURNACE FAN WONT STOP

Christina, Just taking the batteries out of a thermostat might not even disable the thermostat.

Also see

• FURNACE BLOWS COLD AIR

Watch out for air delivery problems

Also remember to check obvious defects that would keep your air handler blower running in heating or cooling mode, such as a dirty or blocked air filter or crimped or disconnected air duct - both of which mean that the heating or cooling system runs but the thermostat is never satisfied so the system keeps running.

Keeprite furnace fan runs at high speed off and on at odd times independent of call for cooling or heating

Hi there,
I have a Keeprite variable speed furnace that seems to have developed a mind of its own.

The fan runs at high speed off and on all times of day and night without the call for cooling or heat. I tried disconnecting the thermostat, but the fan still cycles without it.

There are no error codes read from the flashing light on the circuit board. Do you have any suggestions? Any help is appreciated , THANKS! On 2018-09-06 by Ian

by (mod) - Diagnosing a Keeprite gas furnace fan that won't stop

Ian

Thanks for an important question about what we can almost call a ghost fan controller.

You did the first thing I'd suggest - disconnecting the thermostat wires at the thermostat.

The second step is to disconnect the thermostat wires at the air handler. If this shuts off the fan then the wires are shorted together somewhere.

The third step is to look at the fan controller card or relay in the air handler- more suggestions are in the article above.

AND as a last resort, let's find the model of your Keeprite gas furnace, then we can find the technical or service manual for it.

See KEEPRITE HVAC MANUALS for help finding the manual for your Keeprite furnace if you don't already have it.

Below is an excerpt from the Keeprite/ICP condensing gas furnace manual for the F/G 9MVE model

Adjust Continuous Fan Airflow/Low Speed Cooling Airflow

NOTE: When the furnace is used with a two−speed cooling or heat pump unit, the airflow selected for Continuous Fan via setup switch SW2−3, SW2−4 and SW2−5 will also be the airflow used for low−speed cooling, and vice versa.

NOTE: When the furnace is used with a two−speed cooling or heat pump unit, adjust the Continuous Fan CFM setup switches SW2−3, SW2−4 and SW2−5 to match the airflow required for low−speed cooling.

Select the required Continuous Fan airflow using setup switches SW2−3, SW2−4 and SW2−5 as shown in Figure 5 and Table 5

Heater fan won't stop after changing the air filter

My husband changed the filter in the heater and hit the emergency power off then turned it back on now the fan won't stop running any suggestions On 2017-12-26 by Angie

by (mod) -

That sounds strange indeed.

It's possible that in the furnace he turned on a manual FAN ON switch on the fan limit control, or he might have set the fan to FAN ON at the thermostat.

Try turning the power off switch OFF again, Leave it off for a minute, then turn it back on.

If that makes no difference, check the settings of the FAN switch at your thermostat as well as checking the diagnostic suggestions in the article at FURNACE FAN WONT STOP

Why the Furnace Fan Won't Stop Running?

My furnace fan in my house won't turn off when my unit is off - On 2020-02-01 by Tab

Blower fan continuously running while heat off switches on heat and on auto no fire in the box fan still run - On 2019-11-15 by Jon tester

Sometimes my blower fan won’t shut off for a while. It will work for half the day and then the other half of the day it will not shut off.If I flip the breaker off and right back on the fans stays off until the next cycle. - On 2019-12-28 by Jamie

My Coleman electric furnace will not shut off i have to use the breaker to shut it off - On 2020-12-04 1 by keith

I have a Payne all in 1 blower condenser unit. My blower is staying on all the time. - On 2020-07-13 by Spiro

Blower motor on air conditioner will not shut down. I put in a new control board,that didn't work.put in a new contactor switch.that worked for 8 day's then stopped working.put in another contactor switch .the same. fan motor still runs constantly. - On 2020-03-04 by Forrest

Reply by (mod) - What to check first if the blower fan won't stop in Heat or Cool mode

Jamie and others

First, always check your room thermostat. Has it been satisfied?

Cooling mode: That is, if in cooling mode the thermostat is calling for the cooling system to run until the room temperature drops to the set temperature on the thermostat.

Heating mode: Or in heating mode we have the same problem: the blower runs but the furnace or heater isn't bringing up the room temperature to the thermostat setting.

Is cool (in cooling mode) or warm (in heating mode) air being supplied at your air supply registers?

Other Things to Check

Check the thermostat settings to see if the fan switch is set to ON instead of AUTO

Check the fan limit control in your air handler/furnace to see if there is a manual FAN-ON switch that is pulled out to keep the fan running

Check for a defective fan limit control or fan relay control switch.

Check for shorted wires at a control board or at the thermostat.

Blower still not shutting off? Start by stepping through the Diagnostics given on the page above. Let me know what you find and then we'll go over what questions remain.

 

Sometimes my Amana/Goodman ARUF Air Handler Blower just keeps going AFTER the thermostat is satisfied. Traced to clogged condensate drain.

I've got the same problem, as posted On 2020-03-04 by Forrest.

My Amana/Goodman ARUF3714C airhandler keeps blowing, even after thermostat reaches set-point; compressor shuts down, but airhandler keeps blowing. The problem is *intermittent*--sometimes airhandler shuts off, sometimes it just runs and runs (not the 65-second efficiency delay).

Figured it was the blower delay relay board; replaced it and all seemed ok for a few days. It started up again today. I called Goodman and a tech suggested the thermostat might be defective. I had a new-in-box thermostat on hand, and wired it in.

It's doing same thing--seemingly random failure of airhandler to shut down, after reaching set-point temp.

I'm wondering about either the control wiring, or the 24 volt transformer. We had a power outage a few days before this trouble started, and wonder if the transformer might have been zapped, and isn't putting out 24 VDC.

The other possibility is wiring--if there's some random short or open, responding to equipment vibration or...?

How to check the control wiring? Is "C"/blue the common ground? What wires should be 'shorted' to each other, or to ground, during different operating states? - \2020-07-10 by Steve -

Reply by (mod) - If blower keeps running check to see if the thermostat has been satisfied

Have you tried disconnecting the thermostat right at the air handler? That can rule the thermostat out.

Then before replacing any other parts, check each of the controls.

When the air handler keeps running, the most-common cause is that the room has not been cooled down to the thermostat's set temperature.

So let's check for causes of that trouble, such as refrigerant loss or a compressor that is shutting down.

Followup by Steve

I've already disconnected the thermostat, and replaced it with a brand new one...along with replacing the blower time delay relay board.

Reply by by (mod) -

I got that, Steve, but I'm not clear on whether or not you found that by disconnecting the TT right at the air handler was done at a time when the AHU was running when you think it should not.

Taking that step not only rules out a bad thermostat but also mistakes in thermostat wiring and also the more-subtle problem of thermostat wires that are shorted together somewhere enroute.

Followup by Steve (in GA)

thank you, I shall ohm out the control wires from thermostate mount plate, and check for shorts. Assumption: the W, Y and G should have no continuity
to C (ground), or to each other--correct?

I found a discussion in another forum with same symptoms (intermittent failure of airhandler to stop blowing after reaching setpoint temp), where poster found the G line was left 'floating' (as opposed to being grounded) at setpoint shutdown. He conjectured about putting a pull-down resistor across G and C, to bleed any stray/leftover voltage at setpoint shutdown. He mentioned a 5K.

I just installed a 100K across G and C. Should only load 24VAC transformer with an additional 24mA.

A cooling cycle just completed--system cooled to setpoint, thermostat clicked, and about a minute later, airhandler stopped blowing---good! Fingers crossed that this solved it!

Reply by by (mod) -

Right.

The simplest and most straightforward test is to disconnect a thermostat wires at both ends and then working from each end test for any continuity between any pair of them.

Let me know what you find

Followup by Steve (in GA) - Clogged condensate drain causes intermittent shut down of the A/C system

Well, it turned out to be something verrrrrrrrry simple, but somewhat elusive!

I checked all wiring from tstat to airhandler, and from airhandler to compressor. All lines were continuous, with no shorts to any other lines.

The compressor continued to run intermittently, with no icing seen on coils.

The vent temps were65-66 degrees.

After everything I tried (new airhandler fan delay/relay board, NOS tstat) got same intermittent results, I figured the compressor was shutting down for some type of overheat situation.

The reality...was different....*facepalm*

Contractor came out, gauged compressor and looked at boards on compressor.

He then checked the airhandler, and the condensate float switch (here it comes!).

He saw some water in the switch cup, and said "you've got a clogged drainline. That's what's shutting down the compressor." He blew out the line, and systems been running like a top since then.

The clog must have been *partial*, with slow drainage.

Between cycles, the line would drain enough to let float switch drop, and enable the compressor to run.

The compressor would run, cool the coils, and condensate would begin accumulating-- until it began to back up in the slow drain, and lift the float switch--and shut down the compressor.

I did actually peek in the float switch cup several times, and never saw anything. I must have been looking after it had drained down.

Genteq Endura ECM Blower Fan Runs Constantly - Why?

Thank you for all the very very helpful information found on this website! I am a new homeowner and I found the blower fan (Genteq Endura ECM FM19, 1/2 hp, 230VAC) installed has been running constantly. This is what I have gathered so far:

1. if I disconnect 5-pin low voltage signaling on the ECM, the fan still runs.

2. I checked voltage on the 4-pin power supply to the ECM, they are all correct (C-0V, L-115V, G-0V, N-115V).

3. snap-disc thermo switch checked.

4. heat sequencer checked (I have a heat pump and electric heat).

5. fan relay is quite hard to reach, but when I call fan-on, the relay clicks and the fan blows a little bit stronger.

6. interior of ECM looks great, no dust, no rust, no busted capacitor, perfect rubbery seal.

I suspect the ECM module is programed to run the motor non-stop, by the builder or previous owner? Program # 604253-05. Or what else could be the problem here? Thank you again!

Regards,
Nemo - On 2019-12-04 by Nemo -

Reply by (mod) -

I agree with you that typically there's either a switch set somewhere or a shorted wire or bad control

Is my HVAC blower problem a bad ECM?

Thank you for getting back to me. You mean you think it's the ECM problem (bad or set that way) as well?

What do I need to do, if I don't want the fan constant blowing? - On 2019-12-04 by Nemo -

Reply by (mod) - Check dip switches or jumpers on fan controller

First let's identify the exact brand and model of heater and then look at the manual to see what settings are available.

On most equipment there's actually a user operable switch that will turn the fan to run continuously. But on some it might be a dip switch or jumper.

The other place to look of course is at the thermostat. You can rule out the thermostat by disconnecting the thermostat wires entirely at the heater. If the fan keeps running then it's not a thermostat setting.

Air Handler Blower Won't Stop - Cooling Mode, FAQs

AC is cooling but blower fan won't stop when it should

my ac is cooling fine but the blower fan wont cut off when its time any suggestions - On 2011-06-26 by gene -

Reply by (mod)

See our repair diagnostic steps at these articles

• BLOWER FAN WONT STOP - THERMOSTAT SWITCH
• FAN ON AUTO MAN THERMOSTAT SWITCH
• FURNACE or A/C BLOWER FAN WONT STOP

Heating furnace won't turn off - temperatures way above thermostat setting

At first heat would not stop going up now heat is same but way higher then the setting why won't stop running - On 2018-11-15 by Andrew Anderson

Heating furnace won't turn off - thermostat is turned off

I have my blower motor runs with the thermostat turn off, I change the capacitor and the limit switch it didn't help,the problem occurred when I had a new ac unit out in - - On 2018-10-15 by tony

by (mod) -

Andrew and Tony:

Let's start by checking out the diagnostic procedures at the article for furnace won't stop

There you will find a more complete list of likely causes then what I could make up in a brief off-the-cuff reply. Let me know how that works for you. See this page

FURNACE or A/C BLOWER FAN WONT STOP

A/C shuts off but blower fan continues to run

After my home reaches the temp. I set my thermostat to, the AC will shut off but the fan blower will continue to blow.

If I bump the temp on the thermostat up another degree, the blower will kick off.

How can I make the blower kick off when the temp the thermostat is set to is reached? On 2018-08-12 by Bo

by (mod) - the thermostat is not precisely accurate

Sure the thermostat is not precisely accurate - it's not lab-grade precise.

But if just touching the dial by pushing the temp up - that means setting the temp another degree above the room temp - turns off the blower, then yes, then that sounds like a loose connection or wire or a failing control.

In Cooling Mode & Fan on Auto every morning the fan comes on for a long time - why?

Hello! My Honeywell digital thermostat is set on cooling currently and the fan is set on auto. Everything seems to be working fine, except every morning the blower fan comes on for a long time (an hour or more) even though the thermostat shows no activity (cooling ihas not come on)

The inside temp is already at set point and drops to a couple degrees below the set point within a few minutes of the fan coming on and stays there the whole time the fan is running. This does not seem to happen at other times of day. The thermostat seems to be working the way it should. - On 2020-07-15 by Pam -

Reply by (mod): examples of normal long "ON" cycles in cooling mode

I'm guessing that your thermostat is using a night time setback that drops the call for cooling - an energy savings measure - OR it's simply that where you live the outdoor temperatures drop enough at night that your A/C system can stop running for a time.

Then in the morning when either your thermostat calls for cooling the home to a lower temperature OR when your house starts to heat up from first sun exposure the system turns on and has a longer run cycle to get the house temperature down to the cool setting.

That is, if the system is able to cool your home adequately through the hottest parts of the day it's probably operating normally.

Air Handler Blower Won't Stop - Heating Mode, FAQs

Question: Can blower be deliberately set to run constantly

Can blower running constantly 2019/10/18 Henri Nseke

Reply by (mod) - yes by setting a FAN-ON switch

See these articles for complete detail covering both deliberate running of the blower fan continuously OR accidental or malfunction (the fan doesn't turn off when it should)

• FAN ON AUTO MAN THERMOSTAT SWITCH
• FAN ON SWITCH ADDITION
• FURNACE or A/C BLOWER FAN WONT STOP
• FAN WONT STOP - THERMOSTAT SWITCH

In Heating Mode my ADP Air Handler (w/ hot water heating coil & a cooling coil) pump won't stop running

I have an ADP air handler with a hot water heating coil and a refrigerant coil. My thermostat controls the HW recirc pump.

In heating mode after the recirc pump shuts off the fan keeps running, forever.

I do not see an aquastat or fan limit switch in the housing anywhere.

My question is what controls the fan on/off?

Is it programmed right into the circuit board or am i missing something? - On 2020-11-13 by ovsa

Reply by (mod) - ADP Air Handler with heating/cooling coils: fan control

Ovsa

There is usually a fan limit control in the air handler that turns the fan on or off depending on air temperature sensed in the plenum just above the heater's heat exchanger.

If the fan won't stop on your unit look for one of the controls described at FURNACE or A/C BLOWER FAN WONT STOP and that can be used to manually turn the fan on for continuous operation.

One of those is on the fan limit control, another is often on your room thermostat, and on occasion there may be a fan control right on the printed circuit board in the air handler.

Look furhter for a control board failure: if your air handler does not use a separate timer-containing fan limit control the time delay in fan shut-off may be controlled by dip switches on a control board or by a hard-wired timer.

If you don't have the manual for your unit see

ADP ADVANCED DISTRIBUTOR PROUCTS heating & cooling systems

Or this may be the IO Manual for your unit:

ADP B-Series Multi-Position & Hydronic Air Handlers IO Manual [PDF] (2017) Electric or Hot Water Heat, with available Variable-Speed High Efficiency ECM Motor

Follow-up by ovsa

Thanks.

I looked all through the duct work and there is defintely no controller in there. The stat is set at auto and it is a fairly new stat.
The manufactures data says,

"Time delay for blower activation: 60 seconds (std.)

130 deg. F Aquastat (w/optional aquastat).

So i think that 60 sec delay is just built into the board

I don't see any options or markings for time delay nor any DIP switches.

Anyway I can test it?

thanks for your help

Found a bit more info looking through the data sheets,

Units without Factory Installed Aquastats or Deactivated Aquastats

A time delay of 60 seconds follows before the circuit between R and G are complete activating the indoor blower motor.

The Air Handler fan will turn off 30 seconds after the Thermostat stops calling for heating.

Reply by (mod) - important for the blower fan to continue running for a brief time after the thermostat stops calling for heat

thank you for that it, too. Your paragraph yes I agree and we discussed in this article series The observation that it's absolutely important for the blower fan to continue running for at least a brief time after the thermostat stops calling for heat.

That's to extract the remaining heat out of a heat exchanger and thereby to avoid cracking the heat exchanger from high temperatures which in turn could make the furnace Unsafe and risk carbon monoxide poisoning.

So to be clear we should distinguish between the fan continuing to run for a brief interval typically 30 seconds or a minute after the call for heat of satisfied as distinct from the fan that just runs continuously.

If the fan runs continuously with never shutting off that's the situation discussed at

FURNACE or A/C BLOWER FAN WONT STOP

and is not that purging cycle that you found in the instructions and that we also discussed in this article series

Brand New HVAC blower fan motor keeps running, never stops

Hi looking for some technical help with our HVAC system. I just replaced the blower motor in our furnace and it is running constantly since the change.

I’ve disconnected it from the thermostat to isolate the problem and it still fires up as soon as the power comes on and stays that way with or without the furnace engaged.

The furnace itself still turns on and off as normal so I don’t think it’s the furnace limit controller reading overheat or going bad. I suspect it could be a bad relay.

The thing that really confuses me is that every morning when I wake up it tends to be off and stays that way until triggered either by the thermostat, the fresh air exchange or even me cutting the power and turning it back on gets it going again.

Then it stays running until the next morning again. - On 2020-12-05 by Nathang

Reply by (mod) -

Nathan

Let's start by asking you to review the causes of blower fan not stopping that are given in FURNACE or A/C BLOWER FAN WONT STOP because that's more complete than if I try to make that up again in an off-the-cuff reply.

Please take a look and let me know what you think and let me know what questions remain.

Followup by Nathan

Thank you. I have looked through your article extensively and tested at each place that is applicable to my system. Though I very well could have missed things as I get lost in the different types of systems.
It is an electric heating system with a heat pump and furnace.

1. Thermostat fan set to auto. Still runs all the time. Smart thermostat indicates that fan is off. Thermostat still calls for the fan when the furnace kicks on but when the furnace turns off and the fan is no longer called for at the thermostat it still runs.

2. It doesn’t seem as though there is a shorted wire as when I disconnect the thermostat from the furnace by disconnecting it’s wires at the Air Handler, the fan still runs.

3. There is no fan limit switch that I am aware of. It is a Trane and the furnace is BAY96X141502.

4. This system has a snap disk type limit switch. But I have checked it with a multimeter and it appears to be working correctly. Also the furnace is running as it should, just with constant blowing so if i understand correctly the limit switch would also be keeping the furnace from running normally.

Let me know if i’m missing checking something and I’ll check it out.

Reply by (mod) - Trane air handler using snap-disc & control board for fan limit controls

Nathan

Good going on those diagnostic steps.

You're right that a furnace that uses "snap disc" controllers to manage the fan won't have a Honewyell dial-type fan limit control; but it's of course still performing those functions: fan ON OFF and HIGH limit settings are controlled by those snap-disc controls (whose wiring you may want to follow & check out)

With the thermostat wires completely disconnected at the air handler end, and when the fan won't stop, we rule out an issue with shorted TT wires as well as a bad thermostat or thermostat setting.

Of course "won't stop" bears some clarification: it is proper for the fan to continue running for a minute or so after a call for heat, to extract the remaining heat from the heat exchanger and thus avoid damaging it.

If you are absolutely certain that there is no FAN ON control anywhere on the furnace, and it's disconnected from the thermostat wires at the furnace end then there's not much left: I'd suspect a bad snap disc, (I hear that you tested it), a shorted wire in the air handler, or a bad relay in the air handler.

Other Air Handler Blower Won't Stop FAQs

After upgrading my themostat the fan runs continuously

Recently upgraded thermostat to digital. Now fan continually runs and heat is warm then turns cool.

And the fan won't stop blowing. What did I do wrong? On 2017-11-11 by CJ

by (mod) - Check for mis-wired or shorted thermostat wires

CJ

If those heater problems have happened since the installation of the new thermostat I suspect
- mis-wiring
or
- thermostat wires accidentally shorted together

Saul:

Reasons that a blower won't turn off when the thermostat-set-temperature has been reached are given in the article above starting at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

by CJ

If they were accidentally shorted together what do I need to do? I verified wiring and appears to be correct. I do know that we relocated the thermostat and had to add some thermostat wire to existing in order to reach the spot we wanted.

by (mod) -

CJ

If testing confirms the thermostat wires are shorted together, then you either find and repair the short or run new thermostat wires

 

Furnace fan comes on as soon as power to the electric furnace is turned on

Electric furnace blower comes on as soon as I turn on power at fuse box. If I take out fuses at furnace the elements will heat up. As soon as i put fuses back in fan starts and elements goes out. What could it be? Thanks On 2017-12-28 by mike

by (mod) -

Mike
Since on most forced warm air heating systems the blower does not come on until the plenum has warmed up, and since your system turns on immediately, I suspect that there is either an improperly set FAN ON switch that is forcing the fan into manual on position, or the limit switch is defective

Will the furnace be damaged if the blower fan doesn't turn off?

How long before the furnace starts to get damaged if the fan doesnt shut off. - On 2018-03-07 by Jim

by (mod) - No

Jim

Running the fan continuously should not damage the furnace, but it's true that some fan motors may be designed for continuous operation and others not

I figure that if a furnace was provided by the manufacturer with a manual FAN ON switch on the limit control then the designer intended that the fan could be operated continuously.

 

Where is the blower fan motor switch found?

My blower motor will not stop running unless I turn thermostat down about 10 degrees below temp reading. Where is motor limit switch located? Could it be a faulty thermostat? Thanks. H. Thomas

(mod) - how & where to find the fan limit control switch

Hershel

See FAN LIMIT SWITCH and you'll fin dphotos of the control that give its typical location.

Because the limit control switch has to sense the air temperature inside the furnace it will always be mounted on the furnace, typically on or close to the supply air plenum, thus on the upper are of most furnaces (some oil furnaces locate the control lower in the unit).

The switch will usually be under or behind the furnace cover that's removed to give access to the furnace burner and controls,

or


On some furnaces you'll see the fan limit switch mounted on a supply air plenum (chamber) above the burner and heat exchanger section - that is, at the start of duct work that carries warm air into the building occupied space.

Coleman furnace fan switches tiself from AUTO to MANual

I have an old coleman furnace. The fan wont shut off after cycling. I have replaced the limit switch and fan switch with a universal. I have it set to auto and it starts and cycles fine. During the cycle, for some reason, it will automatically switch from auto to manual thus keeping the fan from shutting off. Any ideas? Thanks, Paul On 2019-01-09 by paul

by (mod) - fan switches tiself from AUTO to MANual

Paul

Thanks for a stump-the-chump question: I am puzzled too. I suspect a bad electrical connection or bad control.

Try going through the fan limit control switch diagnostic procedures at

FAN LIMIT SWITCH TROUBLESHOOTING

and let me know how that works out.

ALSO be sure to confirm that none of your thermostat wires are shorting or touching one another nor loose at their connectors.

Blower fan won't stop and can 't find OEM relay switch - they want me to buy a whole new furnace

Blower fan keeps running and contractors tell me they cannot find the manufacturers original part to replace the failed one and they want us to buy an entire new unit, can anyone help? On 2019-07-17 by Paul

On 2019-07-17 by (mod) - service tech says can't get a replacement control board for my air handler / blower

Paul,

Let's start by identifying your furnace blower unit brand and model; a photo of the unit data tag would be helpful. From that we also want the unit's age, and the country and city where the unit is installed.

Then you can contact the manufacturer to ask their advice. It ought to be possible, at worst case, to replace the blower controller: circuit board and relays; it would be a surprise for the manufacturer to say you have to replace the entire unit. Also there may be third party generic parts that will work.

Suspect bad circuit board causing blower to run continuously

So, hope you can help. I have a blower fan, that does not shut off. This is the same situation on the heat side AND the cooling side. NOTE: When heat or AC itself shuts off, fan slows down, but does not fully stop running. When heat or AC kicks on, it blows at full normal speed.

New issue, did not used to be there, for years. Oil fired furnace/AC unit. Checked all thermostat wiring, no issues. High temp switch checked and replaced( was probably fine). No change. Unit: Carrier 361AAN036075/ Control board Honeywell ST9103A1002

It has been suggested to me that there may be a "cold weld issue" on the circuit board and to replace it. I want a second opinion before I spend the $100+ on a new board and spend the time replacing it. Any help appreciated. On 2019-07-03 by Doug Ziebro

Reply by (mod) - Replacement Blower Fan Relay Switches:

Could be a failure on the control board or on a replaceable fan relay switch. See if your unit has a separate fan relay.

When the system fan should be OFF your tech will check to see if the relay is dropping power to the fan. I'd like to actually do some tests before replacing the board.

Supco relay used as an A/C fan relay switch.

An replaceable electromechanical relay is usually a physically separate device with a visible, moving relay part that you could even push down with a finger (don't unless power is off). There's none in your photo.

Or it's labelled "relay" - here's a general purpose Supco relay used as an A/C fan relay switch.

On 2019-07-06 by (mod) - Goodman Amana Furnace Fan Relay B1370751 B13707-51

And as another example here is a Goodman Amana Furnace Fan Relay B1370751 B13707-51

 

On 2019-07-06 by Doug Ziebro - Bad Fan Controller: Carrier 361AAN036075/ Control board Honeywell ST9103A1002

Thanks for the input. I appreciate it. Silly question...how do I know if I have a replaceable fan relay switch? I know I have a " continuous low speed fan switch", but that is always set to "off".
For a point of reference, I have worked on motorcycles and cars, including rebuilding engines.

I have also fully serviced the beckett oil heater(burner) side of this unit. So Hopefully, I will able to troubleshoot this fan switch. Thanks for the help.

Overheat at resistors on Fan Controller: Carrier 361AAN036075/ Control board Honeywell ST9103A1002

Again, thank you. I was able to replace the board, and luckily, the swap solved the problem. It is amazing to hear the AC shut off, and the fan stop as well.

We have gone for almost a year, having to manually hit the power kill switch, on the out side of the unit. to get the fan to shut off.

The beauty of the internet and the sharing of information, is a truly wonderful thing. Timing is great too, because we are supposed to be getting a 100 F+ heat wave here in NJ this week.

I have attached a picture, with an area circled, where I think the failure point potentially was. It seems slightly burned. Rear side of board looked fine.

One the new board, where the those two resistors are, is a large square block style ceramic heat sink. Makes me ponder of this was a recurring issue, spurring Honeywell to update this control board. Thanks again.

Above: Carrier 361AAN036075/ Control board Honeywell ST9103A1002 - On 2019-07-17 by Doug Ziebro -

On 2019-07-17 by (mod) - replacing control board fixes problem with blower fan that would not stop: signs of overhreating on control board

Doug,

Thank you so much for the photo, the follow-up, and the detailed look at the browning that suggests overheating on the Honeywell fan control board in your air handler - that information will certainly help other readers.

Working together makes us smarter.

 

Furnace fan won't stop running, is the Burner Locked Out?

Furnace fan won't stop running. Owners Manuel says it's locked out. What does that mean was running fine until we changed filter On 2018-11-21 1 by Kristine -

by (mod) -

Locked out usually means that the system burner has shut off on safety because the burner would not ignite.

That doesn't sound like your problem. Check through the Diagnostics giving in FURNACE FAN WONT STOP

Blower Fan is ON and will not turn off. Control board or control board switch problem?

I am having a strange issue that I can't seem to get to the bottom of. Hopefully someone can help!

Blower Fan is ON and will not turn off.

Heat - OFF, Fan - AUTO = Fan stays ON

Disconnect ALL thermostat wires from Fan Control panel = Fan Stays ON

Replaced Fan Control Panel with New = Fan Stays ON

Wacked Blower Motor with BFH = Fan Stays ON - On 2017-12-05 by BenC

Reply by (mod) -

First change the thermostat fan setting: Set fan to AUTO,

then if the fan still keeps running:

- Check the limit switch

- Look for shorted control wires or relay

Followup by BenC

My furnace is an old Armstrong Series III 80 FYI

I now have replaced Limit switch. No Change.

Troubleshooting, I unplug Heat from Fan Control. Then Unplug either Roll Out or Limit. Blower stops, Induc fan turns on.

Replace lead for Roll Out/Limit, Induc turns off and no blower. 2-3 min later

Blower fan starts.

If I do the above sequence and plug in Blue to Heat after shutdown from Roll Out/Limit, blower fan starts with everything off.

Suspect motor or safety control causing blower fan not to work as it siould

I believe the problem is the motor. I have not confirmed this yet. But I have the Heat unplugged from motor control. When I trip the roll out or limit, blower shuts down. Meaning motor shuts down cause board goes into fault.

When time clears blower starts again. There is constant 120 from the board but blower should only start when heat or cool tells it to. With heat unplugged, the only 120 is thru the 120 and com. Which is normal. If it only shuts off when this is faulted and power is cut from these lines, and wires from fan control to blower ohm good, must be short internal on blower motor. On 2017-12-16 by BenC

Lennox blower keeps running, no heat.

Same problem here. Lenox constant blower no heat. no voltage to thermostat. Jumped limit and rollout limit.{they are in series} thermostat was powered and called for heat....for five min. then back to fan only. Do you think it's a circuit board problem? 29 degrees outside on a Sunday On 2017-12-10 17:09:17.594523 by Phil

Reply by (mod) -

Phil and Ben,

I agree that when the control board shows a fault light when the fan turns off that's diagnostic.

But could it not be a different fault - that is not the motor - that the control board is sensing, and in response to that fault it is turning off the motor?

I agree too that if the control board continually feeds power directly to the motor then there's a control problem. But if the board voltage is actually going first to a safety control like the fan limit switch then that's a different situation.

Do you have and did you check the wiring diagram for your unit?

When a blower fan won't stop I wouldn't expect a bad motor to be the direct cause, more likely it's a control or relay.

Worried that my furnace keeps igniting - possible fire hazard

I think my air off and the fan off but my furnace keeps lighting up. I’m worried it with catch fire. - 2019/11/04 Misty Lawhon

Reply by mod:

Misty

I can't tell what's happening with your furnace from your brief text: is the thermostat calling for heat?

Watch out: In any event if you have the slightest worry that the heater is unsafe then

You should shut down the system then called for repair;

 

No Manual Switch on our Honeywell Fan Limit Switch: Should we Keep our Thermostat Fan switch set to AUTO?

If our Honeywell fan limit switch does not have the auto/manual push/pull button for the fan, then is it safe to assume that it is always set for auto?

Our limit switch does not have the hole for the button in the cover, but when opened, it looks like the image above except there is no white button.

Maybe it broke off? (we just bought the house and moved in so don't know).

I read another comment from someone who said that not all models have the button, but our's keeps running well after the temperature is reached.

Any ideas on how to make sure the fan limit switch is set to auto? - On 2020-10-19 by Ed

Reply by (mod) - yes

Ed

Essentially, yes. IF your limit switch has no MAN-ON switch (found as a white push-pull knob or as a small metal slide left-right lever) then yeah that control is in automatic mode.

However some thermostats also include a FAN ON / AUTO / switch that can also control the fan. I'm showing that in the thermostat switch photo just above.

If your fan NEVER turns off regardless of the thermostat setting then I suspect either one of the problems listed

at
FURNACE or A/C BLOWER FAN WONT STOP

OR

one of the situations described at FAN WONT STOP - THERMOSTAT SWITCH

I turned off my A/C off but cool air is still blowing out of registers

I turn my ac off but the cool air was still running .what can cause this problem - Anon On 2012-07-19

Reply by (mod) - AC is off but cool air keeps coming out

I'm guessing either your fan is in manual ON mode or there is a problem with the blower fan relay or control circuit.

See BLOWER FAN WONT STOP - THERMOSTAT SWITCH

and A/C or FURNACE FAN WONT STOP

Furnace fan runs continuously, smell of burning plastic

Fan continuously runs on furnace, replaced the circuit board in March which fixed the issue for about 2 months, back to continuously running.

We did smell what seemed like burning plastic that we couldn't pinpoint, but seemed to be about when we noticed it was running again.

Could there be an issue with the electrical panel because it seems to keep burning out? On 2017-05-25 by Megan Fan

Reply by (mod) - F

Megan,

I agree that it at least appears that there is an external problem hurting the circuit board.

A power surge or a shorted component, or dust, water, debris can also short a board.

Electrical panels don't usually initiate a problem, more likely a damaged or corroded or defective component fails to protect against an overcurrent on a misbehaving circuit.

Watch out: for electrical and fire safety, I'd ask for help from a trained service technician. Your service tech will also check for excessive current draw through the control board, for example due to a failing relay switch or failing electric motor.

Fan sometimes kept running more than one hour after burner has been automatically shutdown

My fan sometimes kept running more than one hour after burner has been automatically shutdown, sometimes the fan stopped just a few minutes after the burner is shutdown.

Is this a problem with the fan limit switch which should tell the blower to turn off when the residual heat in the furnace is dropped to below the temperature setting? Or is just malfunctioning? On 2016-12-22 by Anonymous

Reply by (mod) -

Running the fan for an hour after the burner has shut down means something's wrong. I suspect a bad wire connection or a failing limit control.

The fact that the problem is intermittent also suggests the same diagnosis. If there's no obvious loose wire or loose connection I'd ask for help from a service tech.

 

My furnace blower stops only when is in emergency heat

Anon:

by (mod) -

The blower and furnace should run until the thermostat is satisfied.

If the thermostat is not satisfied in aux heat that may be the trouble.

In other words, your thermostat is calling for heat and is not satisfied until you turn on your backup or emergency heat system. That tells us that you're probably using a heat pump in HEAT mode and outdoor temperatures are too low for it to suffice.

It sounds as if the control that should be turning on back up heat automatically is not working.

Ask your service technician to check that control.

Backup electric heat in air handler shorted and made the fan keep running

Pull electric elements out of furnace and make sure none are touching the frame of the furnace.

I found this condition on a goodman that had the elements and the fan running all the time .

by (mod) - check the backup electric heating elements in the furnace of a heat pump system

Thanks Larry for the good suggestion: a fan control wire or even possibly a thermostat wire shorted to ground (the metal furnace or blower compartment body) should be on our checklist.

Blower turns on and blows cool air even when it's set to OFF

My furnace comes on and runs cool air (we don't have AC) even when I have it in the OFF position of <heat off air> and the auto/ manual fan is in the auto position.

I have the temperature set all the way down to 50 degrees. Where do we start looking? - 2015-08-18 by Mdk 8998

by (mod) - shorted thermostat wires

Check for thermostat wires shorted together

Disconnect the TT wires at the air handler; if it stops running then either the thermostat wires (TT wires) are shorted together or the thermostat itself is defective.

I am going to replace our limit switch as the fan is continuously running

We just found out that we need to replace our limit switch as the fan is continuously running.

I have found one online and will be ordering it, but I have a question about the other limit switch.

The small button style one with two wires attached, the high temp limit thermostat.

When looking at the furnace for the source of our problem, I kind of broke the button one free of the built in frame.

I'm looking to replace that and am having no luck searching the part number located on it, but I have found one with the correct Limit of 300. The only difference is this one has a manual reset button in the center of it, which our current one does not. Is this really an issue?

Can I use the one with the manual reset in place of one without it? As long as the measurements are the same? 2014-12-09 by Amanda

Reply by (mod) -

Amanda

I am sorry to sound like a timid old maid, but if you understand the risks of giving a homeowner advice about heating safety controls you may appreciate that I'm nervous about this.

Watch out: A mistake in installing a limit switch, or mis-handling the switch - say bending a sensitive spring on the dial for example - can put the switch out of proper order and could make the heating system quite unsafe.

For a bolt-on repair when I don't know the part number, I check the installation and maintenance guide for the heating system; if I don't have that document I note the brand, model, serial number and I give the manufacturer a call to ask for the proper part number. Or I might take the old part to my heating supplier for an in-kind replacement.

I would NOT just replace a button type switch based on measurements alone, as switches may look identical physically but may operate at different temperatures.

In general about fan limit switches, the units that do not have the push-pull button are omitting an extra control that let the owner or service tech set the fan for continuous operation rather than automatic.

That's the chief difference.

Fan Limit Switch was Stuck ON - I fixed it myself

After lighting my furnace, the fan kept running and would not stop. After several hours of troubleshooting and following the schematics. I traced it down to my fan limit switch. I removed the switch and found it to be stuck at the on -150 position.

I cycled it by hand a few times and took a wire brush to the base. it had some build up causing it to not release to the off position. After cycling it the switch ended up going back to the off position. I installed it and my furnace now works fine.

Great pictures on this site made it possible for me to fix it myself. Thanks!! On 2014-11-28 by RAY G

Reply by (mod) - Ray's Fan Limit Switch Problem Troubleshooting Tips

Ray you did a steller job of debugging a fan limit switch problem.

And thanks for the nice comments.

But still you should really replace the switch.

Watch out: The fan limit control switch is particularly sensitive to being forced out of calibration, especially if someone forces or pushes on the rotating dial parts - the result could be unsafe as the furnace could over-heat, risking fire, damage, or fatal carbon monoxide poisoning.

Sorry but while you did a marvelous repair I'm left ... worried.

by Ray G

Thanks for the input Dan, I have a new switch on order as I type this. and am making sure the fan runs for a bit after the furnace shuts off, in order to cool the heater box down before shutting off.

by (mod)

Quite right, Ray. That fan run-on interval after the burner shuts off is important to avoid cracking a heat exchanger.

Blower fan keeps running until I tap the Fan Limit Control Switch

The fan starts ok, but keeps running until I tap the limit switch. Have to do this each time or fan keeps running. Is the limit switch bad?

Reply by (mod) - fan stops only if I tap the limit switch

Anon

I'd check for a loose wiring connection first, then if needed, replace the switch.

Is it possible for me to add a second switch in parallel with the over ride button outside the furnace - DO NOT DO THIS

I have a standard domestic gas furnace. The remote thermostat has only a 2 wire run back to the furnace.

I wish to run the furnace blower for long periods to circulate cooler air through the house during the summer.

I can push the manual over ride button in on the high limit switch, which achieves this.

Is it possible for me to add a second switch in parallel with the over ride button outside the furnace so that I don't need to open up the furnace to operate it? Is this a safe practice? On 2014-09-09 by Woolf

Reply by (mod) -

No Woolf,

The push-pull switch on a limit switch used in furnaces is electro mechanical and is an integral part of the control.

Watch out: I would not modify a limit switch in any manner - even if the snafu risks are small it's just not worth the risk of malfunction that can result in killing the occupants or burning down the building.