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Carrier thermostat fan control (C) Daniel Friedman Room Thermostat FAN AUTO ON or OFF Switch FAQs
Diagnosis & repair questions

  • POST a QUESTION or COMMENT about using and wiring the thermostat FAN AUTO, ON, OFF switch control for heating, heat pump, and air conditioning systems

FAQs about the roomor wall thermostat FAN ON OFF AUTO switch:

Questions & answers about how to set, use, or troubleshoot the heating or air conditioning fan control switch found on a room thermostat.

This article series explains the use, setting, and adjustment of the FAN ON- AUTO button or switch or the FAN ON-MAN switch on room thermostats.

This article series answers most questions about central heating system thermostats & controls, troubleshooting, installation, inspection, diagnosis, and repair.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

FAQs on Air Conditioning or Heating System Blower FAN ON-AUTO and FAN MAN-AUTO Settings on Wall Thermostats

Fan ON AUTO switch settings explainedThese questions about the use and repair of the FAN switch on a wall thermostat were posted originally at FAN ON AUTO MAN THERMOSTAT SWITCH - topic home. Be sure to also see that article.

On 2020-10-13 - by (mod) -

Anon

If I understand, your thermostat is set to OFF, and not to "heat" and not to "cooling" but when you turn the fan control to "ON" which is designed to force the blower fan to run, your air conditioner compressor unit (outside) comes-on.

If that's so then there is either a wiring error or thermostat wires are shorted somewhere between thermostat and control board in the air handler or compressor unit.

On 2020-10-13 by Anonymous

With the thermostat off turn fan to on and ac comes on why .

On 2020-01-22 - by (mod) -

Anon:

Please find your question and our detailed reply at

FAN RUNS ONLY ON FAN-ON / MAN https://inspectapedia.com/heat/Fan-Wont-Run-on-Auto.php

and don't hesitate to ask further questions.

Thanks for asking.

On 2020-01-21 by Anonymous

Fan will work only when thermostat set to fan on.
Fan won’t work when thermostat set to fan auto

On 2019-01-05 - by (mod) -

Susan

If the heater runs when disconnected completely from the thermostat wires - at the furnace controller or limit switch - and if it won't run in response to the thermostat I suspect either

the thermostat is mis-wired

or

a thermostat wire (or wires) has been cut or damaged enroute between the thermostat and the control for the furnace

or

the thermostat itself is defective or is not receiving power

On 2019-01-05 by Susan

My furnace wouldnt kick on replaced thermastate but when i take the button off auto on the heater itself it runs

On 2017-12-20 by Carl

I got a honeywell focuspro 5000 tstat in the heating mode when the tstat in auto the fan wont come on but the heatstrips will

On 2019-11-16 by (mod) - My fan wont stop when heat is on

Right, Rick; it's normal that in a residential forced warm air heating system the fan will come on shortly after the burner comes on (giving just some time to warm up the heat exchanger so we don't blow cold air on occupants),

and the fan will run all during the call for heat until the thermostat is satisfied

and the fan may run a little after that as well before it shuts down (that's to extract the remaining heat in the heat exchanger and thus to protect it from damage)

See the abnormal conditions for a fan that won't stop at

On 2019-11-16 y Rick

My fan wont stop when heat is on is that normal? or the fan have to be off when the heat is on ?

On 2019-11-14 by (mod) -

With the fan switch at the thermostat set on auto, turn the thermostat all the way up so you're sure it's calling for heat. Then stand at your furnace and watch the fan limit control dial as the burner turns on. You should see the dial rotate to the point at which it should be turning on the fan.

If it doesn't rotate or doesn't turn on the fan the problem is probably there at that switch. That's something your heating service technician can repair or replace.

On 2019-11-13 by Frank

Heat on thermostat does not work on auto but works when set to on. Ac works fine both ways

On 2019-11-07 04:44:51.680826 by (mod) -

Common causes of the fan running on are in two places


On 2019-11-07 by Dean

When using the heat function and the house reaches the desired temperature the burners turn off but the fan runs non stop even when switch is on auto

...but then when I use the cooling portion and the house reaches the desired temperature the fan does turn off..is the thermastat ok ? Or is the heating relay to blame?

On 2019-10-19 by (mod) -

E

Please post a photo of your thermostat showing its switches, brand, model of you can. Most likely you will be fine leaving it on HEAT mode.

Knowing the brand and model we can check the instructions for your specific thermostat.

On 2019-10-18 by E

When I turn the thermostat to auto for heat nothing happens. But when I turn the on switch I get heat. Can’t keep it running on the ON mode. Help?

On 2019-09-28 by (mod) -

Robert

I'll be glad to help - first please take a look at the live links

Because those two controls usually explain the reason that a fan stays on, in better detail than if I try making it up off-the-cuff again here.

Do not hesitate to ask follow-up questions if either of those articles don't fix your fan-on problem and I'll be glad to take it further then.

On 2019-09-28 by Robert brush

The system is off but fan stays on

On 2019-09-07 by (mod) - thermostat not responding right to room temperature

Let's start diagnosing this problem by eliminating the thermostat from the situation entirely.

AT the air conditioner, where the you find the thermostat wires connected - there the thermostat is acting like an "on-off" switch. Just disconnect the two thermostat wires and jump the two terminals together with a short piece of wire - on the control board. That will call for cooling without the thermostat or its wiring involved.

If the problem recurs the issue is n't the thermostat or its wire.

WATCH OUT: there is LIVE ELECTRICAL VOLTAGE inside any control board or panel - touching the wrong terminals can damage the equipment or can kill you - so if you're not trained and comfortable taking that step hire a qualified repair person to do it for you.

On 2019-09-07 by elvis

what is the problem when my Emerson non-programmable thermostat is set at 65 degrees F, and it cuts off the unit at 77 degreed F?

On 2019-04-22 1 by (mod) -

Kim

If you have access to the thermostat that controls your heat, simply set the thermostat dial (or digital display) to a temperature 5-10 degrees BELOW the actual room temperature (as read on the thermostat) and the heat should turn off and stay off. You don't need to do anything else.

On 2019-04-22 14:11:25.417901 by Kim

Heat on and off switch. What happens inside single stand stove when put on off

On 2019-04-22 14:05:48.792153 by Kim

How to stop heat with out turning off gas fully. Floor unit don't use for anything but winter heat . Stand alone stove heater

On 2019-04-22 by (mod) - how do I turn off heat without turning off the gas supply?

Kim

If you have access to the thermostat that controls your heat, simply set the thermostat dial (or digital display) to a temperature 5-10 degrees BELOW the actual room temperature (as read on the thermostat) and the heat should turn off and stay off. You don't need to do anything else.

You can, optionally, also set the thermostat switch to HEAT OFF if that switch is present - not all thermostats will provide that feature.

On 2019-04-22 by Kim

Heat on and off switch. What happens inside single stand stove when put on off

How to stop heat with out turning off gas fully. Floor unit don't use for anything but winter heat . Stand alone stove heater

On 2018-11-20 by (mod) -

Assuming that you remember to put the thermostat in heat mode, if the blower fan never turns on I would start by watching The Fan limit control switch. You should see the furnace or heat Source come on and the plenum temperature rise and the fan limit switch dial rotate. If you're single of that and the fan is not turning on there's probably a control board, relay, or wiring error

On 2018-11-16 by John

I just replaced my thermostat with a new programmable thermostat. I have a Hydronic air system, boiler, air handler and air conditioning unit. In HEAT mode when the thermostat is calling for heat, the blower fan will not turn on in AUTO FAN, but will in FAN ON mode. In COOL mode the blower fan comes on in both AUTO and FAN ON mode when the thermostat is calling air conditioning. Any idea what would cause this?


On 2018-05-19 by (mod) - no air upstairs

Do you have a separate air handler for your upstairs area? Without knowing anything about your system I can't make very useful suggestion but that's where I would start.

On 2018-05-18 by Jacqueline

Can't get my air on upstairs

On 2018-03-09 by (mod) - heater is not turning on

AB

Let's start with the diagnostic steps given at NO HEAT - FURNACE https://inspectapedia.com/heat/Furnace-Diagnosis-Repair.php

On 2018-03-09 by abuchanan

I use Honeywell thermostat...real simple one. Thermostat click said "HEAT ON" on the panel. But the heater is not turning on. Turning on Fan works but the heat

On 2018-01-09 by (mod) - Vulcan furnace turns itself on in hot weather

Peter,

When an interesting question. Indeed a typical Honeywell fan limit switch uses a rotating dial with three temperature set points to turn the fan on and off; in turn, that dial is caused to rotate by a coiled bimetallic spring within a probe placed in the warm air plenum of the furnace.

It is possible that the supply plenum is getting so hot that the furnace fan limit switch thinks it needs to do a heat purge cycle to avoid heat exchanger damage.

At FAN LIMIT CONTROL SETTINGS - inspectapedia.com/heat/Fan_Limit_Switch_L4064B_Settings.php
we note that

From the factory the FAN ON is usually set to about 130 °F.

So your outdoor furnace plenum air temperature would have to be reaching that temperature for the fan to turn "ON"

Two other articles give reasons that a furnace blower fan may run when you don't expect it to do so, though they're not exactly your situation. Take a look nevertheless for additional operating details found at

FURNACE FAN CYCLES DURING HEAT https://inspectapedia.com/heat/Furnace_Fan_Cycles_During_Heat.php
and at

FURNACE FAN WONT STOP https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

You can answer the question for us by watching the position of the rotating temperature dial on the limit switch.

On 2018-01-09 by peter osborne

I have a gas wall furnace located outdoors which pumps heated air via ducting to all rooms. It is a Vulcan unit, 40 years old, and do not want to replace yet.

On extreme summer heat, the fan on the outdoor unit comes on continuously and blows "room temp" air.

Although the indoor control is Off. Is the cause due to severe heat "tricking" the thermostat or the fan switch in the outdoor unit ? Please advise as annoying to switch off fan at outdoor power point.

On 2017-12-30 by (mod) -

Tommy,

I think you're describing a problem that the heating system is simply not coming on at all. When you force the fan on the fan will push air but the heater is not actually Heating.

You can Use the on-page search box at the top or bottom of this page on this page to find our article series that gives diagnostic steps when you have

NO HEAT, FURNACE

On 2017-12-10 16:01:32.456985 by Tommy

The heat or ac will not come on when set on auto. The fan will blow air when put on on. But will not heat up. Just blows cool air. What's wrong?

On 2017-11-24 by (mod) - smoke coming in at return air inlet?

It's pretty unusual for the return air and a heating system to be bringing in outside air and smoke. I would start by looking at the return air and let's to see where the smoke source is and why you're drawing outside air. Just turning off the fan may stop the problem temporarily but it will also stop your heat.

Take care of that if there's a fire outside you need to turn everything off get out of the house and call the fire department

Watch out: if a heating furnace return air is taking air from near an oil or gas burner that can cause the movement of fuel or combustion odors (gases) into the occupied space and it is likely to create a combustion air defect, or even a fatal carbon monoxide hazard

Also Be sure your building has properly-installed, properly-located, tested, working CO (carbon monoxide) and smoke detectors.

On 2017-11-24 by Joan

The Auto Fan is bringing smoke smells into my house from outside. How do I stop the fan!!!

On 2017-11-19 by Wendy

My fan on my heater keeps blowing and will not shut off the only options are Auto or on. How do I get it off

On 2017-02-07 by Bill

We have a brand new circuit board. It has run fine until yesterday and now the fan always being on auto will not shut off even if we turn the system to off????

On 2017-01-28 by chuck

I just installed a new thermastat. For some reason the fan wont stop when its done with its cycle,and it will not blow heat again unless i reset the breaker

On 2017-01-06 by Anonymous

Thermostat set to auto its on heat and runs all time will not shut off

On 2016-12-11 by Anonymous

i have a lennox G1201-82-1 the heat and blower wont shut off, instulled a new thermostat and is set to atuo. there is no heat pump.

On 2016-12-04 by Mark - I don't think the fan should be blowing 24/7

Rheem blower doesn't shut off in heat mode. Had 2 new units installed with heat pumps. Heat strips were also added. Everything was installed in march.

So I used the Ac thought the summer with no problems. Unit would turn on and cool and shut off normally. Now I switched to heat and the blower does not shut off.

According to my thermostat once the selected temp is reached you hear a click and the light/lights turn off but the fan continues to blow non stop. As the temp goes down in the room you hear a click and the light turns on and starts to heat the house again.

This continues 24/7. I'm setting the heat anywhere between 65 to 68 degrees. Only way to turn off the fan is to turn system to off.

I have checked to be sure it is set to auto. I did look at the thermostat wiring guide and noticed the B wire (blue) reversing valve (heating mode) is wired and in the book says activates reversing valve in heat mode-ALWAYS ON in HEAT MODE

I pulled the thermostat off and disconnected the blue wire....didn't get any heat out of the vents but when I lowered the selected temp to at or below the current temp the you hear a click and the lights go off and the fan stopped.

I'm not an expert but I don't think the fan should be blowing 24/7 which would cause for a high electric bill.

On 2016-10-26 04:24:13.299948 by Anonymous

Heater running constantly won't shut off

On 2016-09-13 by (mod) -

Antoine

As you've disconnected the TT the trouble could remain as shorted TT wires - so try disconnecting them at the blower unit. If the fan keeps on, see FAN WON'T STOP - LIMIT SWITCH at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php for help in diagnosing and fixing the trouble.

On 2016-09-13 by Antoine Sayegh

HI,
My ac blower fan wont shut off. I tried to set the fan on auto, turn(AC) it to off on thermostat; the AC shuts off but fan keeps running. I changed the fan relay, same issue. I disconnected thermostat , fan still runs. The cooling process is runniong properly with temperature settings. Any help appreciated. Thanks

On 2016-07-29 by (mod) -

Thanks for that added detail, Gene, it'll help other readers.

On 2016-07-27 by gene woodfin

my tempstar air handler their are two paths to the fan run relay. In the fan switch on mode your turning the fan on thru a n/c contact on the relay. In the auto the 24vac takes a different path thru the fan limiter unit n/c contact

On 2016-07-27 by (mod) - In AUTO mode, the fan won't turn on until ...

Gene

In AUTO mode, the fan won't turn on until other conditions are met, such as the thermostat calling for heating or cooling. The fact that the fan runs in ON or MAN means that the trouble is not in the fan itself.

If your thermostat IS calling for heating or cooling but the fan won't turn on, there may be a problem with the fan relay or control board in the air handler.

If your system is in HEAT mode, then yes the fan limit switch could be in trouble.

On 2016-07-27 by gene woodfin

my tempstar nugg075df03 air handler blower wont always turn on in auto mode but will always turn on when fan on switch is actuated.I have checked all voltages at transformer 110/24vac replaced thermostat suspect fan limiter is the problem. what do you think!

On 2016-07-20 by (mod) - when the fan won't turn off

Susan, a hot water boiler system doesn't use the FAN ON OFF AUTO switch discussed in this article. At least not in most system designs.

If your A/C system is set to AUTO and never turns off

Set the thermostat SET temperature to above room temperature as shown on the thermostat

. If the system does not shut off after about a minute, then I suspect that thermostat wires are shorted, there is an A/C control board problem, a relay problem, OR someone has turned on a manual FAN ON switch in the air handler itself.

See these diagnostic articles

FAN WONT STOP - LIMIT SWITCH

FAN WONT STOP - THERMOSTAT SWITCH

On 2016-07-20 04:13:05.432320 by Jennifer

My thermostat is set on "auto" however, my fan won't shut off at all, ever. I have a hot water boiler for heating, if that is relevant. Even if I shut my air off the fan continues to run even though is set to auto. Help!

On 2016-07-20 by Susan again

Not sure I asked the question correctly....I have a hot water boiler system for heating. I also have an air condition unit and the coil sits inside the ductwork. I have my fan on auto at the thermostat but whether it is calling for cooking or not, the fan never shuts off. How do I fix this.

I forgot to say the FAN won't shut off.

I have a hot water boiler system and an air conditioner. I have my air conditioning set on auto but it never shuts off. How do I fix this?

On 2016-07-05 by (mod) - Fan set to AUTO means the fan will run automatically when the system is cooling (or heating)

That's right: Fan set to AUTO means the fan will run automatically when the system is cooling. But the fan setting does not call for cooling;

The thermostat switch needs to be set to COOL and the thermostat temperature control needs to be set below room temp.

Search InspectApedia.com for DIAGNOSE LOST COOLING to see detailed suggestions

On 2016-07-05 by Elle

I have put the air conditiner fan on auto but on thermostat i shows cool on. So trying to figure out what went wrong..help pls..

On 2016-06-19 by (mod) - Temperature raises back on the thermostat quicker then it actually does in my house

I'd ask my heating service tech to take a look at the thermostat location and the cooling requirements of the space; if the thermostat is in a location where it improperly senses room temperature (exposed to sun, drafts, supply air) that could be the problem.

On 2016-06-18 by Dee Cooper

Hi, I have a question about my a/c unit. I have a two ton unit, my pressures are reading correct levels, I have new filter in my return, new thermostat wired correctly with fresh batteries

My unit will get to the satisfied temp and will not cut off within the time frame. I have been mainly raising temp to make it understand it is satisfied and it immediately shuts off like it should.

Temp raises back on the thermostat quicker then it actually does in my house; therefore turning the unit back on.

After about 7p.m., I can set it to 70 degrees and it will run for about an hour and satisfy. I do have vaulted ceilings in my living room, however; my house is very small under1200 sq.ft.. What else do I need to check or do? My electric bill of course is high. HELP!!!

On 2016-06-06 by (mod) -

Yes indeed. That tends to give more even temperatures, does more air particle filtration, and ... in this case won't work too long if your HVAC tech doesn't find and fix that squeak: it could be a failing bearing.

On 2016-06-06 by ellen

is it okay to have my FAN ON set on the furnace, and my air conditioner set to come on at a certain temp? I notice since the air conditioner has been kicking in now that it's hot, the FAN on the furnace blows constantly but makes a tiny "squeak" sound when the air conditioner kicks in and of course the fan goes into high speed or something or more forceful. I'm wondering if the "squeak sound it makes when switching is normal and safe".? thanks very much

On 2016-05-16 by Angie

My Carrier heat and cooling in one system (heatpump). I can turn my fan to on and it runs but if I turn on the heat or air I can hear the unit outside running but I get no air (fan) flow from my vents. Can you help.

On 2016-05-04 by (mod) -

If the blower fan works normally on a call for heat or cooling I suspect a wiring or controlberror.

On 2016-05-03 by Anonymous

The fan will not run when the stat is switched to fan on

On 2016-04-29 by Brent

if the heat cool switch has been set off does the fan still run if set to on?

On 2016-04-07 by (mod) - fan cycling on and off every 2 seconds

Perhaps a bad thermostat, a bad wire, or a problem at the heater and its controls.

On 2016-04-07 by Alpha

If i set my thermostat to auto it keeps coming on and off every 2 secondes what may be yhe reason

On 2016-03-28 by (mod) - Some blower on-off cycling is normal

Some blower on-off cycling is normal, such as running on for a minute or two at the end of a heating cycle.

See also these two articles

https://inspectapedia.com/heat/Furnace_Fan_Blows_Cold.php - FURNACE BLOWS COLD AIR -

and

BLOWER FAN OPERATION & TESTING at https://inspectapedia.com/aircond/HVAC_Blower_Fan.php

On 2016-03-28 by Ned

Even though the thermostat is in the off position, the blower fan will turn on and off by itself. What can cause this?

On 2016-02-14 by (mod) - power outage loses thermostat settings

Craig if you had a power outage, lost power to the thermostat, or had to change its batteries it may be running on a temporary program and needs to be re-set to the program you want.

On 2016-02-14 by craig hewitt

My furnace thermostat is saying temporary on it.
want to known what to do ?

On 2015-12-28 by (mod) - what to check first when the blower fan won't turn on

Check for an open door to the blower compartment or to a dirty or blocked air filter.

On 2015-12-27 by carla

doesn't matter what we do the fan will not turn on, everything seem ok in our thermostat but out home is not cooling down there is a red light on in the furnace.

On 2015-12-03 by (mod) - the fan cycles on and off even when the furnace burners are not on

Carm

I'd say it happens but it's not necessarily "normal" in the sense of "correct" for the furnace fan to keep cycling;

See https://inspectapedia.com/heat/Furnace_Fan_Cycles_During_Heat.php that explains why a fan cycles on and off when you don't expect it to.

Then check out the fan limit switch for proper operation at

BLOWER FAN OPERATION & TESTING

On 2015-12-03 by Carm

thermostat is set to auto ,yet the fan cycles on and off even when the furnace burners are not on is this normal.

On 2015-08-07 by (mod) - keeping air moving will generally improve dehumidification and will keep indoor temperatures more even

I tend to agree with your co-worker at least in theory; keeping air moving will generally improve dehumidification and will keep indoor temperatures more even. But the specifics of your office HVAC design might make your co-worker shoot herself in the foot with the pistol of my advice.

As my HVAC genius Mark Camer (Tampa Florida where it's plenty hot) says, "... it depends"

If the return air inlet for your system is picking up very hot air from an inadequately cooled space then when the A/C compressor itself is not running it might blow too-warm air especially on occupants under supply registers closest to the hot return innlet.

The thermostat location can also make trouble - if the thermostat is "satisfied" and turns off cooling while some occupied spaces are still too hot that's the problem. It's especially tricky to balance cooling in office areas if people subvert the system by closing some registers, opening others, or removing suspended ceiling tiles, all of which were not in the plan of the HVAC designer.

Start by lowering the thermostat setting a few degrees while leaving the fan ON.

On 2015-08-07 by Sherry

Need help with an office dispute. Our central system has heat/air and auto/fan/off switches. Outside daytime temp has been in the upper 90's for about a month, with weeks more to come. A co-worker insists on moving the "auto" switch to "fan" resulting in warm air filling the suite and the temperature increasing about 10 degrees F.

He says this is to "keep the air circulating". While this sounds right, I can still feel the uncomfortably warm air every time he moves it. I was taught, firmly, that the setting should remain on auto at all times. Your thoughts?

On 2015-06-29 by (mod) - system only allows me to choose 'on' or 'cool'.

Linda I'm not sure which thermostat your system uses - brand and model, so I can only guess. If this thermostat ONLY is used for cooling I suspect that "ON" forces the fan on continuously and "COOL" puts the system in cooling mode. You'd want to use COOL.

On 2015-06-29 by Linda

I live in an apartment. The air condition system only allows me to choose 'on' or 'cool'. The system will not allow me to choose 'auto'. The system runs continually. Between 'on' or 'cool', which of the two settings should I keep the system on? Suggestions?

On 2015-05-18 by (mod) - can't the the house cool enough

Johnny,

Start by asking your HVAC technician to measure the operating temperatures of the system at the cooling coil and at the supply register outlets.

Also measure airflow. Before knowing how the system is working - or if it's working - we can't begin diagnosing the trouble.

On 2015-04-24 by johnny g

I have a split entry style house & Sears installed central air thats connected to my furnace.

My problem is, set temp at 68 & can't get temp. lower than 75 (floor registers)& never shuts off,but family room in basement goes below 68. I have an insulated attic & the ac just can't go lower than 75 on the main floor,why?? Can i add a fan booster to force more air up through my floor registers?? or any suggestions to fix this??

Question: blower does not shut off

(Aug 19, 2014) Brian said:
I have my air conditioning set on auto and set a on schedule for Day at 26 and Sleep 25 and cool is on. The problem is cool air comes through the vents but the blower fan does not shut off when it reaches 26, it runs continuously and after a few hours it will no longer produce cool air. What is the problem?

(Mar 2, 2013) Anonymous said:
My heat will not work in auto mode, the flames light but the fan wont come on please help

Sophia Castella said:

using this service i have able to showing my room as any front of company member really its a great post.
northernbeachesair in Australia - gas heating Dee Why

Reply:

Interesting, Brian, I'm not sure.

If the room temp satisfies the thermostat it should shut off the equipment.

But thermostats are not necessarily absolutely precise instruments.

If room temp is actually just below the trip-off point for the thermostat and the AC system is not able to drop the temperature further (for example because the cooling coil is frosting over, impeding airflow) then the system might keep running.

Your second point about no cool air makes me think that the coil is iced OR the compressor is staying off.

Question: blower runs continuously and loud thumps occur when cooling cycle ends

(Aug 19, 2014) Nate said:
I have an open floor plan/vaulted ceiling/two story home which is very difficult to keep evenly cooled in the summer. It seems to help to run the blower fan continuously but I have noticed a loud thump inside the home when the cooling cycle completes. To clarify the FAN is always on, when the condenser starts its cycle, I get a loud thump inside the house. This thump does not occur when the FAN is set to auto and it turns on at the same time as the condenser. It seems/sounds like the thermostat or something else in the system is telling the blower to turn off and then back on again.

I can imagine this is good for the blower. What can I do to stop this?

Reply:

Nate

Have you checked for

- loose motor mounts at a blower assembly or fan

- sudden pressurization of metal ductwork causing a section of duct to flex?

Question:

Nov 3, 2014) Anonymous said:
system will heat but if you turn it on to auto the fan will not come on

(Nov 16, 2014) Pat said:
I have an electric heating unit that just won't stop running even if I lower thermostat or switch it to off...help

(Nov 27, 2014) Anonymous said:
fan will not run in auto mode

Reply:

Anon if a heating or air conditioning fan runs in MAN mode then we know the fan itself, its motor, and electrical power are working properly. That leaves us looking at the thermostat wiring, thermostat settings, and possibly control board or relays on the other end of that wiring.

Question:

(Dec 19, 2014) Anonymous said:
I am using the A/C heater. I have it set at 73 / the blower does not cycle on or off after the temp has been reached, but the temp does does not rise above the 73 setting. Why? I have fan set at auto.
Sly

Reply:

I may have misunderstood but it sounds as if the fan is not running when the heat point on the thermostat is satisfied. Which would be correct.


...

Continue reading at FAN ON AUTO MAN Thermostat Switch - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Fan & Limit Switch Repair Aritcles

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FAN ON AUTO MAN Thermostat Switch FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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