White Rodgers furnace gas valve wiring?

[Darrell Woolaver]

Hello, I noticed today that the wiring going from the Honeywell spark/controller unit to the gas control valve. (White Rodgers 36E24-204) is not wired according to the diagram. I replaced the controller with this Honeywell S8670K unit about 10-11 years ago and it has been working fine BUT I noticed today that the common on the gas control valve is connected to 24V-ground and not the designated MV/PV common port on the control unit. Yellow lead goes from 24V ground to the gas valve and then in turn another yellow lead comes off of the gas valve back into the furnace somewhere.

Everything is working ok and has been like this for years so I'm guessing that 24v ground and MV/PV common must be electrically equivalent?

I'm inclined to move yellow wire jumping off of the common directly to the control unit and then connect the common to the MV/PV pin as this is what wiring diagram show it should be. But I'm certain the old control unit which was replaced must have been wired like this which is why the MV/PV common is not used on the replacement Honeywell spark unit? pics attached.

 

[Fitter30]

Transformer common is also grounded to the furnace cabinet. Look on the wiring diagram blower door common o f transformer will show it.

 

[Sponsor]

 

[Darrell Woolaver]

Transformer common is also grounded to the furnace cabinet. Look on the wiring diagram blower door common o f transformer will show it.

Thanks Yes, I traced the yellow wire that was piggybacked off of the common junction on the gas valve down to a "C" pin on the fan motor board.

I went ahead and moved things so that common on gas valve is connected to the dedicated MV/PV common on the spark controller and then moved the yellow going to the common below to the 24V-grnd port. (which is where it was before)

I think you are saying that 24V(transformer)grn and the MV/PV common are both grounded to the cabinet chassis? If so my moving of wires did not actually do anything except perhaps make me feel better because the wiring now matches diagram for the Honeywell spark control sticker. This would also explain why everything worked fine in the previous configuration.

 

[Plumber69]

I think it is just a loop, the new ones you have to move the 24v to the thw extra prong

 

[Plumber69]

Spark ignition on these furnaces where stupid