My furnace blower motor will run properly on "Auto" but will not operate at all on "On".
What's going on?

Thanks,
trazmo

I forgot to mention, I have replaced the thermostat (Honeywell electronic).

Trazmo

Time for you to revist your thermostat install. The G terminal is what controls the manual operstion of the blower. If not the wiring then check the thermostat setup program to be sure all your settings are correct.

Thanks for the input. Done what you suggest, all is correct. I was having the problem before the new thermo, that's what prompted me to install it.
Any other thoughts?
Thanks,
Traz

If it is working correctly at this point the job is done since I am sure you caulked or plugged the area where the thermostat wire comes through the wall on the back side of the thermostat. This prevents inner wall drafts from creating problems with the thermostat temperature sensing device.

What type of furnace? Model?

Comfortmaker
GUH100A016CIN

trazmo, are you sure of the model #? Can't seem to find anything using that number. I think HVAC1000 (he's the expert) thinks your problem is solved, you might need to repost. Good luck

I just picked back up on this. I misread the post and thought the problem was over. Usually the furnace blowers ON thermostat selection is controlled by a relay. On newer furnaces this relay is located on the circuit board but older units have a stand alone relay. I have located your furnace BUT I have no wiring diagram for it. Does you furnace have a circuit board?

Yes, it has a circuit board

Usually the circuit board contains the blower relay. See if there is 24 volts from the thermostat green wire to ground. This is at the G terminal in the unit. The G terminal is what activates the blower when using the ON selection at the thermostat.

I checked out the board and a lead was burnt out. I reapaired it an now motor run normally in both the "on" and "auto" positions. Thanks for the suggestions they led me in the right direction.
Over and out,
trazmo

Glad you got it running.