I have a Janitrol U-29A that is probably about 8 years old. I don't when it started, but sometime over the summer it began acting up. The blower does not stop blowing air unless I turn off the furnace at the circuit breaker. The AC unit outside turns on and off through the thermostat, but the heater does not come on and the unit just blows the air it pulls from the house.

I checked on here and some other places and the most common answer was check the thermostat. I went out and got one that has some nice features (and even if it is not the thermostat, it will be nice to have this new one rather than my old turn dial one) and replaced the old one.

About a year ago something happened to the furnace and the control board got fried (it looked like it got a drop of water on it and it would not even turn on.) I checked for similar issues and there is nothing that I can see.

I have seen places on the web say it could be a temperature control switch, but I could not find anything mentioning that in the parts manual. I was wondering if you all might think that could be an issue ro if I should check something else.

Thanks for your time in advance,
Jon

The most likely problem is the relay that controls the blower. Unfortunately, likely it is on the control board you just replaced. I guess you could be lucky and it is still be under warranty.

There is a limit switch somewhere around the heat exchanger that turns on the blower when the heat exchanger is warm. It could be stuck. However, with the furnace not coming on either, I would bet the control board is bad.

Thanks I will check it out. I hope it is under waranty, though I doubt it... oh well at least I have experience replacing them. :)

Ok I'm going to assume that you have a gas or oil furnace. There are limit swiches all over the furnace. These switches keep your furnace safe. When one goes bad or is doing it's job the furnace will not run and fan ususlly keeps blowing in order to cool the unit down. You may also have a bad fan relay in the unit. It is time to call in a qualified service person to check out your unit.

The board has a diagnostic LED. Any activity?