Replacing 2 Hunter thermostats with a Honeywell RTH9580 Wifi. Neither unit has a C wire – I'm comfortable with the upstairs high efficiency unit, but the downstairs older unit has thrown me for a loop.
The Hunter has cables connected to G-RH-Y-W, with proper color coding. There was a spare wire – so no problem, go downstairs, connect to C, and I'd have my 5 wires, good to go. But… when I got downstairs I found the "Y" connected to "C" on the unit, and the Y terminal had no wiring. I bought the house this winter, so its never run the A/C. I'm beginning to question what would happen if I flipped the switch to COOL!
There are secondary wires jumpered off that run to the compressors – but I'm not understanding how to fix the wiring. Can I just move the wire connected to "C-Y" to "Y-Y" and use the spare wire to connect to "C-C"? Or is there some reason a unit would be wired to "C" on the unit and "Y" on the thermostat??
Best Answer
The YELLOW or Y terminal at the furncae/ air handler is a dummy terminal for convenience, it is not required to be used, you could send Yellow directly to the AC unit out doors. Common will be used since the Common leg of power comes from the transformer which is in the furnace. The Yellow going to common likely if you trace it back it in fact is Common leg of the 24 v power supply.