Furnace blower does not turn on in the auto position

**vlee1973** · 10-28-2010, 10:49 AM

The furnace lights up, but the blower will not turn on if I have the thermostat in the auto position. The blower will turn on if I turn the thermostat to the fan position. I have Ultra II 90 high efficiency furnace
maid by Magic Chef. Any help would be greatly appreciated.

Vince

**Thatguy** · 10-28-2010, 11:59 AM

Originally Posted by vlee1973

The furnace lights up, but the blower will not turn on if I have the thermostat in the auto position. The blower will turn on if I turn the thermostat to the fan position.

The blower comes on in the auto mode based on time or on duct air temperature.
If it doesn't come on I hope the hi temp limit switch kicks out? Otherwise you are in danger.

Can you post a schematic? Do you have a multimeter?

**jimbo** · 10-28-2010, 01:22 PM

There is a temp. sensor which delays blower start until the heat exchanger warms up. Need to replace that sensor, or possibly the fan control relay board.

**vlee1973** · 10-29-2010, 11:34 AM

Sorry about the wait guys. The furnace does turn off after a couple of min. I could get my hands on a multimeter. I have added a couple of pictures.

**Thatguy** · 10-29-2010, 01:18 PM

Originally Posted by vlee1973

The furnace does turn off after a couple of min.

So your hi limit switch works.

The schematic is illegible but if it weren't there would be some crucial circuit test points you could check. My camera has a close up option but this same schematic may be online somewhere.

You should probably find out why your furnace housing is rusting. Maybe water is dripping from that blower housing in the upper left.

**vlee1973** · 11-01-2010, 10:17 AM

I changed the temp sensor and everything is working like a champ. I will look into the rusting problem. Thank you for all of the help Jimbo and Thatguy.

Vlee