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SF 42 furnace madness

Lt46
Explorer II
Explorer II
So, turned on heat and got fan but no ignition. Pulled furnace and cleaned, while also doing a tune-up. New sail switch, new overtemp switch, new ignitor and new burner installed. Bench tested 12v + and 12v- connected, jumpered the 2 blue wires and got fan, gas valve click and ignitor sparking. All looks good so far. Re-installed, connected gas line, checked for 12v+ and 12v- at connection and is good, jumpered the 2 blue wires again and the cycle began as expected. Fan operated, click from gas valve and ignition of gas producing heat. Yeah, still good so far. Shut it down and went inside, set thermostat to 90*, set mode on T-stat to HEAT and NOTHING, no fan, no click, no spark, no nothing. What the heck is going on? Further investigation reveals my t-stat will not turn on the AC fan or AC cooling either, no nothing. This is beginning to look like a t-stat failure??? BTW, the 2 amp fuse in the t-sat checked and OK but I put new one in, just to rule it out. Anyone else have any ideas?
Thanks
Peter & Dawn
[black] 97 Winnebago Adventurer 37RW [/black]
F53/460 w/ tag axle
[black] 96 Prowler 27X SOLD[/black]
IAFF L-792 (Ret.)
17 REPLIES 17

Lt46
Explorer II
Explorer II
Thanks Chris. I have 8 wires coming out of the t-stat with only one blue wire. I'm not understanding what you mean about swapping the blue thermostat wires?
Peter & Dawn
[black] 97 Winnebago Adventurer 37RW [/black]
F53/460 w/ tag axle
[black] 96 Prowler 27X SOLD[/black]
IAFF L-792 (Ret.)

Lt46
Explorer II
Explorer II
Thanks Chris. I have 8 wires coming out of the t-stat with only one blue wire. I'm not understanding what you mean about swapping the blue thermostat wires?
Peter & Dawn
[black] 97 Winnebago Adventurer 37RW [/black]
F53/460 w/ tag axle
[black] 96 Prowler 27X SOLD[/black]
IAFF L-792 (Ret.)

Chris_Bryant
Explorer II
Explorer II
Try swapping the blue thermostat wires- one supplies 12 volts to the thermostat.
-- Chris Bryant