Howdy

Came home from work and the fan for the HVAC is running. It's set to auto so it shouldn't come on until the temperature gets above the a/c set point on the thermostat.

Indoor temp is already 2 degrees colder than the set point so no need for the thermostat to signal anything to come on.

I turned the HVAC to "off" even thought it should not be necessary. Flipped the fan switch to "On" for a bit and then back to "Auto" in case it's a switch problem (that's my guess) but that didn't do anything.

Kill the power at the breaker and see if that resets anything? The thermostat has (I believe) a battery backup so killing the breaker shouldn't do anything but turn off the fan.

Suggestions?

have you had any work done recently? maybe you have a manual switch at the fan that accidently was switched on? or possibly a stuck switch/relay up there. If you haven't had any work done recently and this just started, probably need a new thermostat.

I'm with RoyVal on this one -- I'd look for a stuck time delay relay in the air handler.

Usually those are delay on 'off', so that the fan runs about 30 seconds longer after the compressor shuts off to clear the cold air out of the ducts and warm up the coil.

I've had them both stick 'on', and also stick 'off', which causes the compressor to run with no indoor blower.

Of course, mine is an older air handler that uses electro-mechanical relays. If you have an new-fangled system, it may all be controlled by an electronic circuit board.

If it's the former case, the parts costs less than $20.00.

Good luck.

No work recently.

My brother just told me similar thing. Relay stuck in the air handler or thermostat.

He recommends killing the breaker and then pulling the face off the thermostat and then closing the breaker. If fan comes on, it's the relay. If it doesn't, it's the thermostat.

Sound correct?

Opened the breaker marked "heater"

That stopped the fan

Took all the wires loose in the thermostat

Closed the breaker

Fan kicked on

Opened the breaker again. We weren't going to need the heat or a/c tonight anyway

I'll get up in the attic in the morning and see about this relay business

Slap an Ecobee in there while you're at it.

maroon barchetta said:

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Opened the breaker marked "heater"

That stopped the fan

Took all the wires loose in the thermostat

Closed the breaker

Fan kicked on

Opened the breaker again. We weren't going to need the heat or a/c tonight anyway

I'll get up in the attic in the morning and see about this relay business

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having that fan on 24/7 isn't going to hurt anything until you can get it figured out (really wouldn't hurt anything long term either). I wouldn't turn the breaker off if it was me. If anything...you're find it might make your house temps more consistent from room to room. Let us know if/when you figure out the problem.

I'll let you know. I have the breaker off for now and am out running errands and will get in the attic later.

Thankfully the temps are mild so we wouldn't have we been running it anyway.

Just fyi. Our fans run constantly at our house

All it does is circulate the air better

Our ceiling fans run a lot. We don't want our air handler fan to run when it's set to not run!

RoyVal said:

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maroon barchetta said:

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Opened the breaker marked "heater"

That stopped the fan

Took all the wires loose in the thermostat

Closed the breaker

Fan kicked on

Opened the breaker again. We weren't going to need the heat or a/c tonight anyway

I'll get up in the attic in the morning and see about this relay business

---

having that fan on 24/7 isn't going to hurt anything until you can get it figured out (really wouldn't hurt anything long term either). I wouldn't turn the breaker off if it was me. If anything...you're find it might make your house temps more consistent from room to room. Let us know if/when you figure out the problem.

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Can't speak for other parts of the country but in central Texas if the ac is on and you leave the fan on all the time instead of auto you will have much higher humidity inside. I have seen as much as 10-15 % even almost 20% higher humidity on numerous residences versus when the fan is set to auto. Have also seen mold/mildew grow on things such as pillows etc when the fan was set to on and it ran for multiple days caused by the excessive humidity levels. The problem is when you leave it on all the time, the constant airflow continues to cross over the wet coil that is no longer cold once the compressor has turned off so you end up reintroducing humidity back into your residence.