Fuse for Furnace

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AJW

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Joined
May 5, 2013
Posts
33
Location
Alberta CA
2013 Itasca Sunova 33C For the life of me I cannot find the 12 volt fuse for my Suburban SF35 furnace. It quit working (fan does not come on) but the thermostat works for the heat exchanger and AC. There is 12 volts across the white & blue wire at the thermostat and there is 12 volts at the white wire at the furnace. The trouble-shooting guide says to check the fuse. I have downloaded the wiring diagram (Wiring INSTL-Body , 12V # 180335-02) from Winnie but there is no fuse shown! All it shows is "4pin HSG to Furnace". I suspect the problem might be in the furnace itself. Any suggestions?
 
I think you will find the the "demand for heat" wire is a different terminal on the thermostat in each case. On the Coleman Mach thermostat/basement air combination used in my 5th wheel,  the wire to the furnace is part of a 3 pin plug, the other 2 being 12V+ and -12V, the battery and ground supply to the thermostat itself. The demand wires for cooling and heat pump are part of the second (9 pin) connector.  For starters, with the cover off, it can be checked for +12V right at the thermostat after placing the thermostat in Gas Heat mode and raising the temperature  or by simply jumpering the +12V directly to the furnace lead and the fan will (should) start. If it doesn't, you could well be right and you will have to dig around the wiring at the furnace end. (You might find an inline fuse back there or a connection that has come loose. My furnace connections are all wire nut connections, no plugs, and they can come loose.)
 
If the OP has the usual basement air heat pump and gas furnace configuration, odds are good the wiring is the same as mine. If he has roof air, then you are most likely correct.
 
Looking very quickly at your truth table John, my thermostat/furnace/air conditioner wiring seems identical to yours. The only obvious difference is that the 3 pin plug was cut off and wire nut connections were used behind the thermostat. (Alfa was too cheap to furnish the 3 pin connector required as it was to be supplied by them. The 9 pin connector was supplied as it was part and parcel of the umbilical cord to the AC unit...)
 
AJW said:
2013 Itasca Sunova 33C For the life of me I cannot find the 12 volt fuse for my Suburban SF35 furnace. It quit working (fan does not come on) but the thermostat works for the heat exchanger and AC. There is 12 volts across the white & blue wire at the thermostat and there is 12 volts at the white wire at the furnace. The trouble-shooting guide says to check the fuse. I have downloaded the wiring diagram (Wiring INSTL-Body , 12V # 180335-02) from Winnie but there is no fuse shown! All it shows is "4pin HSG to Furnace". I suspect the problem might be in the furnace itself. Any suggestions?
Click to expand...

AJW
Do you have 12V at the RED wire at the furnace?

On my coach the furnace fuse is in the House Fuse Panel... which is located in a bedroom cabinet.

(The House Fuse Panel also contains the fuses for the interior lights, power vent, water pump, water heater, refidgerator and the TV antenna booster).
 
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