Trying to figure out some HVAC wiring.  House has a 1 stage air conditioner, 2 stage furnace that’s wired as a 1 stage, and it has (1) a Fantech FG8 fresh air intake fan that is ducted into the HVAC return plenum, and (2) a 150 cfm laundry room exhaust fan that is apparently also tied into either the furnace wiring, the air intake wiring — or both — presumably so that the laundry exhaust fan comes on when the air intake fan comes on in order to balance out pressure.  The Fantech FG8 air intake fan is also tied to the kitchen’s range hood and comes on automatically when the range hood is turned on.

 

I have attached a picture (the only one I have) of the wiring at the furnace board.  I think it shows:

 

The brown 24v wire bundle marked with the red arrow appears to be coming from the a/c condenser and is connected to the common and Y terminals on the furnace as expected.

 

The brown 24v wire bundle marked with the purple arrow appears to be coming from the thermostat and is connected to common, G, W, and Y, as expected, but the R wire appears to be going into a blue wire nut (circled in yellow) rather than to the R terminal on the furnace.

 

There’s a gray 24v wire bundle marked with a blue arrow.  This appears to have an orange wire and a red wire going to the R terminal of the furnace board, and a green that is connected in the blue wire nut to the red wire from the thermostat.

 

It’s mostly this gray 24v wire that I’m not understanding.  Why is the red wire from the thermostat bundle wire-nutted to the green wire from the gray bundle?  And why are red and orange wires from the gray bundle connected to the R terminal of the furnace board?  I’m guessing that it has something to do with the interplay of the furnace, Fantech FG8, and laundry room exhaust?  I understand that nobody will know for certain based on this description and this picture, but if anybody has some idea of what might be going on here, some guess, some speculation, etc., I’d really appreciate hearing any ideas.  Thanks!

Update:  The system also has one of those hockey puck style wet switches.  I posted a similar message on another forum and somebody commented that the wiring setup likely had to do with the hockey puck wet switch, rather than the Fantech or exhaust fan.  I’m thinking the hockey puck answer is probably correct and would be easy to verify just by looking to see where the gray bundle goes, but I’m not at the house to check for a few days.