I bought the wrong thermostat. I discovered this today, two months after installing it, when we went to run the air conditioning and it was blowing out heated air. Which is not ideal when it’s 84 out. So today is when I learned the difference between single stage and two stage thermostats. My immediate concern was to get the air conditioning going, and then deal with the problem of installing the right thermostat later.

This entry is meant as a reminder to myself so that, come December when we need heat again (this is Florida, after all), I’ll know what to do. Assuming I haven’t put a two stage thermostat in place before then.

The wiring to enable cooling on my two stage system using a single stage thermostat is:

Old stat -> New stat
G -> G
C -> Taped off
R -> R
R and Rc jumpered
Y -> Y
O -> W/O/B
W2/E -> Taped off

When I want to enable heat again, pull and tape off the O wire and put W back into W/O/B.

The *old two stage thermostat* wiring was:

The *new single stage thermostat* wiring was (before doing the A/C fix):

Again, after the A/C fix the white wire is taped up and the orange one is in W/O/B.

In the stat setup, function 1 = 1 and function 2 = 0.

Once it’s time to install the two stage, the wiring will be:
G -> G
C -> C
R -> R
R and Rc jumpered
Y -> Y
O -> O/B
W2 (white) -> Aux
Aux and E jumpered

Then function 0170 = 7, 0910 = 0, and 0270 = 9. That applies to RTH7500D and RTH7600D