Older continuous blower unit fan operation questions & answers.

This article series explains how and why to set your air conditioning or heating system blower fan to continuous operation in order to improve indoor air quality by increased and continuous indoor air filtration.

Q&A on Why Run an Air Conditioner or Heating Blower Fan Continuously

For maximum indoor air qality (IAQ) improvement in buildings: for a new blower installation we selected a fan unit which had both the capability of delivering adequate CFM of air flow and a blower fan motor duty cycle which permits continuous operation if we wish to run the system that way.

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These questions and answers about running an air handler blower fan continuously were posted originally

at BLOWER FAN CONTINUOUS OPERATION - be sure to read that article.

On 2013-03-24 by (mod) -

Dean

Check that the push-pull switch we describe above is not in the "ON" Position.

If the fan is not in forced "ON" either at the fan limit switch or at the thermostat, I suspect that the control switch itself may be bad.

Try turning off power to the unit completely, Wait 30 seconds. Turn power back on.

If fan won't stop the control is bad - or you've missed one of the switches we discussed.

On 2013-02-24 by Dean Dressler

How do I turn off a stuck fan blower which is from a 1991 Carrier HVAC system. The heater and AC works fine but I just can't shut of the fan.

Recently, my 21 year old carrier HVAC blower is stuck on when it is in the "Auto" position. How do I shut it off or ...????

Thank you, Dean (562) 833-4472

On 2012-11-24 by luci

How do I know if the fan blower motor is rated for continuous operation and is there any proof that it raises the electric bill? I have pets in the house and I notice that it helps with the hair and dust if it is kept running.

On 2012-10-07 by (mod) -

Edgardo,

Search InspectApedia for "odor diagnosis & cure" for help in tracking down odors and smells to their source.

On 2012-10-06 by Anonymous

I have a 1968 solid metal air duct system and 1995 Emerson 3.5ton heatpump.

I bought the house in Austin TX june 2012. It is a fixer-upper. Recently, with cooler weather, when I come into the house, I start tearing, getting a headache, runny nose, and smelling a strong odor which I cannot identify (I am from NY, no mold/fungus/ allergy experience prior to arriving in Austin). Replacing ac system is >>>$$ and would not include air ducts replacement.

I have not seen any mold but in a 1968 abandoned, tenant occupied house, I'm sure there is....need help.

The headaches stop as soon as I go outside. Did not occur until last week (first wk of OCt 2012). Help!!! ivm1@columbia.edu Edgardo, who is your AC contractor?

On 2012-08-18 by Tim

My fan motor in the air handler will not turn off. The thermostat is set on Auto. The compressor turns on and off when it should. How do I fix it so it works as it should in Auto?

On 2012-08-13 by (mod) -

Spence and David D there is no reason at all why a thermostat can't be used to control the fan in a duct system - just ask your HVAC tech to wire it up for you. Instead of calling for heat, the thermostat can simply turn the fan on or off at a given temperature range.

The rub may be that no matter how long the fan runs it won't, in some conditions, cool the house enough for the thermostat to ever tell the fan to turn off. For this reason, most folks simply manually turn the fan on and off when they want it to operate.

In fact there some attic vent fans that work this way, though as I explain next, those can pose a fire hazard.

We don't want a themostatically operated attic fan or whole house fan without some special fire safety controls as in event of a fire we wouldn't want that fan to come on and increase fire draft.

On 2012-08-12 by Spence

How can I find out if my fan is rated for continuous duty operation? Thanks.

On 2012-08-12 by DavidD

Can or is there a thermostat to control the fan only on a unit?

On cooler days we open the windows however our house does not circulate air well on its own so we turn the fan on and let it run to circulate air.

Is it possible to say get a programmable thermostat that can run the fan only say for 15 minutes, or some other programmable time, and have it run say every 90 minutes or some other time programmable of course.

On 2012-08-10 by mdalimd68@yahoo.com

ther no thermodinamice systam miller chart

On 2012-08-08 01:18:04.164899 by (mod) -

Rob

Interesting. I suppose thermostat contact bounce or a bad heat anticipator or bad TT could be at fault - I'd try removing the TT wires from the TT and tying them together to call for cooling - if the system runs ok then we know it's the thermostat. If the problem continues it's the TT wiring or a control board.

And of course check out and clean/free up that zone damper.

On 2012-08-07 by Rob

It sounds more like the Auto setting is sending Open and close signals to the zone damper and the zone damper is stuck or something and gives off a rythmic ping 1 2 ping 1 2 ping etc. Also, I have noticed condensation water splashing out from around the white drain pipe, almost like the drain is clogged and water is trying to find a place to go. I think something shorted out from the water maybe?

On 2012-08-05 by (mod) -

Rob, if you heard the vent/duct noise when the equipment was not running then it's probably not the equipment itself but perhaps duct noises that occur due to a temperature change (cooling night air, shrinking sheetmetal).

On 2012-08-05 by Rob

Last night we were awoken by a pinging noise coming from the vents that stopped as soon as we clicked the fan switch to on. When we switched back to auto the ping noise happened again. It sounds like something is broken somewhere in a damper or something. Anyone know what could cause this?

On 2012-07-05 by (mod) - the A/C works with the thermostat (TT) set in "AUTO" but when you turn the fan to full-time "ON" the A/C will not turn on at all

Not sure, Linda. I think you're saying the A/C works with the thermostat (TT) set in "AUTO" but when you turn the fan to full-time "ON" the A/C will not turn on at all

. If that thermostat control setting is the ONLY thing you're changing, and provided you're not in the process moving the system out of COOL mode, I'd suspect a switch problem in the thermostat, in a relay or control board in the equipment. Perhaps you can send me a photo of your thermostat and its controls.

On 2012-07-05 by Linda

The air conditioner is working fine and delivering cold air but when I have the fan on the "on" position, it just won't come on. What might the problem be?

On 2012-05-29 by (mod) - If you have no cool air or not enough cool air the system will just keep running

Annie Marie B.

If you have no cool air or not enough cool air the system will just keep running as the thermostat is never satisfied. Provided both indoor and outdoor units are running, and airflow is not blocked (say by a dirty filter) you need a service call.

Diagnostic details are at LOST COOLING CAPACITY (search this website for that article0

On 2012-05-29 by Annie Marie Bonniville

about my centeral air conditioner if the weather is 80 out side and I set my thermo at 72 my air conditioiner never cut's off HELP HELP THANK'S

On 2012-05-04 by Bart

Hi,
My A/C isn't coming on, so we first checked the thermostat. I used a jump wire and when I jumped R and W together the fan blower came on but the unit itself didn't kick on.

I then jumped the Y and G terminals to test the thermostat, but the fan blower didn't come on. I read where if the blower doesn't come on when jumping the Y and G terminals that the problem was not likely the thermostat.

We are going to buy a new thermostat(probably need a newer one anyhow) and intall it. If this does not work, what would be the most obvious problems that I could check myself? We don't have the money for a repairman.. Thank you

On 2012-05-02 by Greg

AC and fan run continouley what should I check?

On 2011-11-27 by (mod) -

Chris: yes running the fan alone when you are using an independent heat source will help distribute heat to other portions of the home. But WATCH OUT: an open fireplace, even if it warms your living room, will virtually always operate as a net heat loss for the building. If the fireplace has a source of outside combustion air and a glass door to prevent sending room air up the chimney and a heat exchanger you may get some net heat gain. Otherwise it's a net loss.

On 2011-11-27 by (mod) -

Nancy - be sure to see the article titled DEHUMIDIFICATION PROBLEMS (in the ARTICLE INDEX found at the end of this article)

On 2011-11-27 by (mod) -

Nancy, if your A/C system is not cooling AND presuming that your air flow is not restricted by a clogged filter, crushed duct, dirty blower fan or coil, etc., then it's possible that your A/C system is not properly sized for the home.

Combined with that problem if your building has a source of excess moisture (wet basement or crawl area, lots of steamy showers, poor exhaust venting, pasta cooking, large number of occupants, etc), a portable dehumidifier may lack the capacity for the total space you have combined with the moisture source.

Frankly I would never expect a portable dehumidifier placed in a hallway to be capable of dehumidifying an entire multi-story home. It just can't move enough air through itself and won't pull from nor deliver air to the more remote rooms.

I agree that undersized ductwork or inadequate return air can severely limit the capacity of your central A/C system.

I'd have an expert examine the HVAC system entirely: duct system, blower unit, cleanliness, air filter condition, type and location, etc. before making any costly changes in the system. It seems odd to me to be considering adding a "dehumidifier" to an existing HVAC system that already has air conditioning. Properly sized and installed, the air conditioning system should be doing the dehumidification.

Finally, a thorough inspection of your home for moisture sources, leaks, etc. sounds needed as well.

On 2011-11-27 by Nancy

In the summertime, our R.H. reached 70%.

It was so bad, that the moisture from the (many) showers we take condensed from the air onto two INSIDE WALLS, with drip marks flowing down the walls. We will be installing vents in our two upstairs bathrooms in the next few months, which I believe will make a big difference. However, in September we purchased a dehumidifier to put in the hallway between the two bathrooms.

With it running 24/7, we couldn't get the R.H. below 60%, on all three levels of the house. Even now, when we have our heating on, as soon as the temperature outside warms up a bit, the humidity in the house shoots up.

Three major problems we have: Our air conditioner doesn't cool the upstairs (other floors fine), we only have one return vent upstairs, and since we installed a high efficiency furnace, the moisture problem has definitely gotten worse. I want to install a central dehumidifier, but we have a TRANE furnace and I've been told that only the same brand dehumidifier can be installed.

Is that true?

And is it true that only having one return vent upstairs will prevent the dehumidifier from being effective upstairs? I know this is a lot of information, but we're getting desperate.

On 2011-10-23 by Chris

When I am burning wood in my fireplace (in my living room, where the thermostat is), of course the fire warms the living room up, but the rest of the house is cold. If I run my fan only, during this time, then will that circulate the warm air through the rest of the house?

On 2011-10-03 by (mod) -

Hillary, running Just the A/C fan will move air and make for more even temperatures in the home and it will increase the level of air filtration. If that is enough to make you comfortable without running the A/C system, it's certainly less costly.

If your outside unit never ever stops, you need a service call.

On 2011-09-10 by JBB

I noticed frost build up on my home AC evaporator unit. The filter is cleaned, thermostat is fine and the Ac unit blower cools and stops properly, but the condensor fan unit outside does not stop instead runs contnously. The only way I switch off condesor fan is by Circuit breaker switch in garage . Any trouble shoot suggesstion is appreciated

On 2011-09-10 by hillary

hi I am wondering if having the fan on my thermostat ON, but the actual air conditioning, OFF, does that save me power? or am I basically just over working the fan and not gainging any energy saving benefits?

On 2011-09-08 by (mod) -

Sorry Charlie, I can't guess. See if you can dig up the model and serial number of your equipment, then take a look in the installation and operation manual there. Or is your thermostat a programmable one that is turning off the fan?

On 2011-09-07 by Charlie

Why does my continuos fan opration shut off over night?

On 2011-09-07 by (mod) -

Gil, thanks for that helpful and interesting comment. I agree completely and will add your comment to the article text.

On 2011-09-07 by Gil Vice

An additional benefit of continuous fan operation is reduction of bioaerosol growth (mold etc.)

During cool periods (like overnight), the AC is off and the coil and drain pan warm up. The longer the fan is off, the higher the relative humidity becomes in the air handler, limited only by how much water was in the drain pan. If there is sufficient humidity, microbes can grow anywhere in the air handler there is even a spec of dust. Running the fan continuously keeps relative humidity in the equipment to the level of the rest of the building.

This even helps compensate for a poor installation with an improperly leveled drain pan.

AC disinfectant tablets can also help. Most people will never notice this problem, but mold sensitive people can start experiencing problems with brand new systems in the first month of operation. If you are using AC to help allergy problems, consider running the fan continuously.

On 2011-08-25 by (mod) -

Shery, I agree that shorted TT wires could be continuing to call for the fan to run. Just first check that no one has turned on another switch to force continuous fan operation.

For example, at the air handler unit of combination A/C and heating systems there is a fan limit switch that may contain a white button that can be pulled or pushed out or in to run the blower fan continuously.

I'd ask the tech why, if the motor runs, the problem is the motor and not a control or control circuit?

On 2011-08-24 by Shery;

Air handler won't shut off even with Thermostat in auto position, A/c unit runs fine and shuts off fine, air handler just keeps running, tech said needed new motor, I say it may be a electric shortage or thermostat connection problem ? any thoughts ?

On 2011-08-12 by (mod) -

Edgardo because this humidity problem diagnosis talk may be helpful to other readers, I've preserved our discussion just above. We appreciate the debate and welcome your further observations.

On 2011-08-07 18:59:22.710179 by Edgardo

Another disadvantage I found running the AC fan continuously in my residence, was a noticeable increase in the humidity in the house. The fan would blow across the wet coils and drain pan while the compressor wasn't running and put the water it had removed from the air during the prior cooling cycle back into the living space. So I stopped doing that.

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Continue reading at BLOWER FAN CONTINUOUS OPERATION - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BLOWER FAN OPERATION & TESTING
• FAN WONT STOP - LIMIT SWITCH
• FAN WONT STOP - THERMOSTAT SWITCH
• AIR HANDLER / BLOWER UNITS - home

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BLOWER FAN CONTINUOUS OPERATION FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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