I have an old 1980 era mercury analog thermostat, and want to replace it with a programmable one. The system coontosl a gas furnace with external compressor. The old t-stat is a general electric, and has the following wire conventions:

Wire Terminal
Green G
White W1
Yellow Y1
Orange Y2
Red RH and jumped to RC

The new thermostat, which states is for multi-stage units, is a Hunter Autotemp Heat pump multistage programmable.

Terminals avail, and wires that seem to go to them:

Wire Terminal
Green G
Red R
Yellow Y1
White W2
C
L
O
B
E

There is a designation on the terminal block for W1 and Y2, but no way to connect them (no screw terminal). I am not sure what to do with the orange wire that was connected to the Y2 terminal on the old t-stat. Any suggestions will be greatly appreciated-
Rock

Try this for help.

https://www.askmehelpdesk.com/heatin...tml#post220523

Thanks for this. I am still unclear on whether if the orange wire is the Y2 (second stage cooling) and the terminal block on the thermostat does not have a Y2 on it, will I damage anything not connecting the orange wire for now ( in winter?)

Do you really have a modern 2 stage A/C?
If not a heat pump just leave orange off

OK, I have more info.
It is a heat pump system, 2 stage, General Electric furnace and thermostatt. There are 2 mercury swicthes in the old one.
The problem I have now is the Hunter thermostat (model 44760) states that I MUST connect the common wire, however, there does not appear to be a common wire run to anything on the original t-stat ( see original post)... plus still don't know whether to connect the orange one to anything.
Thanks again. I am about ready to just call a service technician

I should also add that there are blue and black wires that were taped offf with the old thermostat. Is it possible one of these ( the blue one) is the common wire? I am using a volt meter; touching the red wire with any of the others gives a reading of about 30 acv, but touching the red and blue, or the red and blackI get zero...

Go to the air handler or where ever the other end of the cable is. If neither the blue or black is connected to anything, pick one and connect it to the common at both ends.