Troubleshoot furnace wiring from converter.

[SaSuVa]

The title is vague at best, my apologies.

I purchased a 2007 Gulf Stream Conquest with a Suburban furnace. The furnace did not respond to the thermostat. The fan does not start nor any other function.

The thermostat furnace wire coming from the converter does not have any voltage. When I apply 12vdc to the thermostat furnace socket, I get no response from the furnace.

I feel this is a ground problem and it may come from the control board of the furnace. I can jump the wiring at the furnace and initiate the blower, but it does not cause the furnace to ignite. Oh, the blower motor fan was completely full of wasps nest. I removed the nest and tested the blower. It works.

Where to start? Well I guess i have already started, the question is, what steps do I take to determine what the problem is and resolve it?

Thanks Sam

[BFlinn181]

I think I'd start by unplugging all wires and connectors to the furnace control board. Spray with contact cleaner and reconnect them. Perhaps a bit of corrosion is the problem.

The furnace should get power from the house fuse panel. The thermostat should send a trigger signal to the furnace. Look up your thermostat make and model online to find a manual for it to check its hook up.

The house fuse panel gets power from the converter/charger and the house batteries. If you suspect a bad ground connection, a jumper wire is a handy way to make a temporary ground connection to see if it's the problem.

I'd also remove the wasp's nest on the fan blades and clean to make sure it's still in balance. Hopefully, the fan motor is O.K., it should be thermally protected from overheating if stopped.

[SaSuVa]

Thanks for the reply Bflinn181, wasp's nests removed. The problem was the wiring at the a/c was disconnected, I assume because of the furnace attempting to operate, making some noise and the owner worried about damage. They simply chose to use electric heat instead of repairing the furnace.

There are two white wires coming from the control box in the ac unit. They BOTH connect into thermostat wire bundles. However, a close examination of the wiring diagram finds that two blue/white wires(14 guage) from the a/c control box connect to a white wire(18 gauge) and a red wire(18 gauge), from a two-wire thermostat bundle. these two wires(red and white) go to the furnace.

The single white wire(14 gauge) from the a/c control box connects to a white wire((18 gauge) in a thermostat bundle, I think it was a 5 or 6 wire bundle. That wire goes to the thermostat.

Connect the wire and the furnace works, who knew!?!! Normal furnace operation, fan, heat and it shuts off just like new.

Interestingly:
1)When the a/c control box wire is disconnected from the thermostat. the thermostat lug for furnace will flash a 7vdc approximately when changing from "furnace" to "off" to "cool", that makes diagnosing difficult. 2) When selecting "furnace" at the thermostat, the a/c fan will come on until the wiring is connected, then the a/c operates normally. 3) I tried to connect the furnace directly to 12vdc(at the blower connector on the furnace), while I could get the blower at the furnace to turn on, the furnace did not operate. When I tried to connect the furnace wires at the a/c control box to direct 12vdc power, the furnace would not operate.

Hths,
Sam