[wirepuller224]

Just moved into another house, and there are 2 - 2conductor cables disconnected from the furnace PC board

One is from the a/c unit which turns on but doesn't kick on the furnace fan

The other is from the main bathroom exhaust fan switch . This is a 2 pole switch ( 1 pole is the 120VAC for the bath fan , the other is dry contacts to turn on the furnace fan ) and I gather the idea is to run the furnace fan whenever the main bath fan is running to avoid negative air pressure in the house which could lead to CO being back drafted down the chimney

I need to reconnect these but cannot read the diagram inside the furnace cover, faded/blurry
Which terminals do these go on and can they both go on together

[Joshdta]

I have never once seen a bath room exoust fan tied into the furnace wiring. New one to me. What are the open terminals left on the board? And are you sure that's where they come from?

[wirepuller224]

I live in Northern Alberta, Canada and apparently it's a building code requirement here that when the main bath fan (usually at least 135 CFM ) is running, the furnace fan must also run to avoid negative air pressure in the house. Possiblly to do with our extreme winter temps ( as low as -50 F)

Terminals are as follows

TWN Y W R G C

Open Black Blue Red Green Open

Thermostat is a Honeywell TH6110D1039 Programmable

Thanks for the quick reply