RV furnace electrical

[jjrbus]

Electrical is not my strong point and the older I get the worse I get, but this should be very simple! I have a 94 Toyota RV with a Everest star 79/80 Series furnace. The wireing and plumbing in the RV were a bit of a mess when I bought it and I am getting it back together.

I wrote down everything as I removed it, but did not test the furnace beforehand. When I hook this up it blows the fuse!

The red #3 to thermo and +12V on schematic is not making sense to me and I suspect I am missing a ground wire?

Can anyone help me with this or tell me the right questions to ask?
Jim

[img] [/img]

[jjrbus]

I left out just a wee bit of detail so as not to muddy the water's. The existing red and white I referred to go into the loom and emerge as green and clear at the thermostat. The lack of an existing ground wire has me baffled, but it is a Florida vehicle and the furnace at 22 years old looks unused!

[wa8yxm]

As someone said, Black is Ground, the Red wire is +12 volt and also power to the thermostat, The remaining wire is signal FROM the Thermostat (+12 volt means "i'm feeling chilly", high resistance (no voltage) = "I'm feeling warm")

Very standard.. On my unit however the wires to the T-Stat (Both of 'em) are blue,, but there is no color standard so what you have is normal.

[jjrbus]

No idea what the original fuse size was and not in the owners manual. The manual does show that the furnace draws 1.2A, I will ask on the Toyota forum.

Seem to have success. There was no ground wire at the furnace? Added a ground wire and fan comes on. No gas so cannot test further. But no sparks, smoke or blowing fuse.

Thanks much greatly appreciated. Jim

[westend]

What size fuse blew that was original? My WAG would be 10A but I don't know the draw of the ignitor.

[jjrbus]

Many thanks for the responses.

The existing grey wire is the 12V+ power supply from the 12V DC distribution panel.

While we are at it, What size fuse should this have? Jim

[Old-Biscuit]

The RED is 12V POS from the DC DIST Panel (FUSED) and goes to the factory On/Off---circuit breaker mounted on the frame of furnace.
That same 12V DC (fused) goes to 'R' on t-stat

79/80 Hydraflame

OP...not sure what you mean by 'grey to 12V fuse block' ??

[westend]

You need to have Red (#3) to a circuit breaker. This circuit breaker protects the power feed to a relay and then to the gas valve and motor of the furnace.
If you are blowing fuses, chances are that you have the power shorted to ground somewhere. I'd suggest to get some help, this is an easy circuit to wire correctly.

[Chris_Bryant]

In that picture, the black is ground, red is both +12 and to the thermostat and White is from the thermostat. No ground to the thermostat.