Furnace questions

[RockcrawlingTJ a.k.a. Justin]

I understand a furnace should run for a few minutes to push all of the hot air out of the ducts and from the coil but our furnace never seems to shut off. It works fine, heats the place just fine, just doesn't seem to shut off when it should.

Can I adjust the program? It started to do this with the new thermostat but has increasingly become more pronounced the past month or two. It was 80* in the house this morning, thermo set to 68 and it was still running (just the fan).

Thanks.

[CSP]

Does your thermostat have a fan switch that gives the options of "On" and "Auto"?

Sounds like it does and it's set to the "on" position.

Edit: or does it eventually shut off?

[Jeff Mason]

There should be a low limit heat switches, if I remember correctly. Basically, they tell the fan to stop running if the temperature of the air is below 'x' amount.

I'll bow out of this and wait for Frank Z or one of the other qualified guys to answer.

[Jeff Mason]

http://www.inspect-ny.com/heat/FanLimitSwitch.shtml

[RockcrawlingTJ a.k.a. Justin]

Yes, it has an "On/Off" position. When the fan is running, even if I turn it to off I have to go to the furnace and take one of the covers off that has a pressure switch. I then have to leave it off for the majority of the day before putting it back on, otherwise it kicks right back on. This is a random issue but it is happening more and more often.

[zillacon]

Brand age of the furnace would help?

[RockcrawlingTJ a.k.a. Justin]

http://www.inspect-ny.com/heat/FanLimitSwitch.shtml

Sweet, I'll check that as well...

[RockcrawlingTJ a.k.a. Justin]

Brand age of the furnace would help?

Make and Model:
Rheem RGAC-080A

I think the furnace is original to the house - "a - 1980" is stamped on the tag within the unit.

It's a little dusty in there but I cannot seem to find the fan control as mentioned in the link. I'll do some Google searches on the unit itself.

[zillacon]

If you post a pic of the controls I'll point it out to you. If the heat was running and you said it got to 80 deg. and not just the fan alone running I would rule out the fan control. Something is calling for heat! I would start by looking into that stat of yours. If you need some more help send me a pm and I'll give you my # to see if I can help you over the phone.

[RockcrawlingTJ a.k.a. Justin]

If you post a pic of the controls I'll point it out to you. If the heat was running and you said it got to 80 deg. and not just the fan alone running I would rule out the fan control. Something is calling for heat! I would start by looking into that stat of yours. If you need some more help send me a pm and I'll give you my # to see if I can help you over the phone.

I'll drop you a PM - to clarify the heat actually turns off but the fan does not stop, blowing cool air out of the vents. As the day gets warmer the house naturally begins to heat up putting the room with the thermo to 80* at times. If I turn the thermo to the 'off' position the fan continues to run until I take the cover off with the pressure switch.

[Digger]

I had this happen one time with a furnace. As Jeff suggested there is a temperature (limit) switch located in the ducting of the furnace that turns the blower on when the air is warm enough and then turns it back off when the burner shuts down and the air cools off in the duct again.

Mine looked like a control box mounted to the outside with about a foot long wand that protruded into the furnace duct.

Follow the electrical leads from the blower and I'll bet you find the thermal switch.

[RockcrawlingTJ a.k.a. Justin]

http://i9.photobucket.com/albums/a74/RockcrawlingTJ/ATT00014.jpg

[Jeff Mason]

It's almost summer. Shut off the gas, hit the breaker, and forget about the problem until October :D

[RockcrawlingTJ a.k.a. Justin]

LOL I thought about that but I'm going to list the home and do not want to leave the new owners with an unforeseen problem they'd have to deal with down the road.

[zillacon]

I cant see the pic at work but I'll chime in when I get home.

[CSP]

The picture looks like it is the box where power comes into the furnace. I don't see any controls.

[zillacon]

The fan control is the silver cigarette sized box that says honeywell on it. If you need a replacement call of Federal Heating and air. They sell to the general public.