Suburban furnace won't start

[Boharris]

I have just purchased a 1998 Thor California Tahoe TT. All works but I can't the get furnace fan to start. A/C works as it should with the Duo Therm T-stat. I have pulled out the furnace and have power directly to the fan but no power to the red wire directly across on the 4 pole relay on the motor (not sure if i should). I can jump the +12v and the Heat on the t-stat and the fan will run for about 30 seconds or so then stop. What do i need to check next or change?

[Boharris]

Good news here too. Jumped Furnance to 12v on old Duo Therm and all came on and worked perfect. Home Depot $18 Honeywell T-Stat and away we go. A/Cond is even shuting off with temp setting. Woo Hoo.

Many thanks for all the above advice.

[facory]

Had the same problem. I pulled the thermostat and found a corroded connection where two points come together to make the connection. Looks like the old points on cars. If you find this take a small piece of emory cloth and gently clean them.

[Boharris]

Will try it!

[enblethen]

If you have a combination thermostat, try resetting it. Some have a fuse that you remove for 15-20 seconds, then reinstall to reset. After re-installation of fuse it takes about 15 minutes to reset.

[Boharris]

Also have noticed my a/c will not shut off when cold. I have it really cold in there and the t-stat set on 90 and it's still running. Think maybe the t-stat is bad and the furnace is not seeing the set temp to even come on? i set it to 90 and still no furnace fan. I will check the sail switch tomorrow anyway.

[enblethen]

The relay is a time delay style. You will not have power across until it times out which should be 10-15 seconds.
Locate your two wires, normally blue, coming from the thermostat. Connect them together. The fan should start immediately, time delay relay should time out supplying power to the circuit board, via the over temperature device and then the sail switch.
Sounds like you could have a dirty sail switch. Locate it and blow it out good with air.