Hi,

I am replacing an older Honeywell Chronotherm III (T8601 C1021) with another newer Honeywell Chronotherm III (T8600 D1111) and there is not a C terminal on the replacement unit.

The original wiring configuration was (wire color > terminal):

White > W
Green > G
Blue > C
Red > R
Yellow > Y

And on the new thermostat, it has onlt the following five terminals: W, G, R, Rc, Y.

So, where does the Blue wire connect on the replacement stat? And the Red wire?

Seems straightforward to connect White > W, Green > G, Yellow > Y, so that's been done.

But it is not clear where the Blue wire or the Red wire connect?

Trial One: Left Blue unconnected, and connected Red > Rc, and the a/c worked perfectly, but no heat.

Trial Two: Connected Red > R, and nothing happened.

Then I gave up for fear of damaging either the stat or the system.

Please let me know if you have an idea for the correct terminal for the Blue wire and the Red wire connection.

And perhaps also let me know why Honeywell would eliminate the C terminal for this nearly identical newer unit and not reference it anywhere in their support material.

Thanks,

Baffled in St. Joe (MI)

The blue--c--common isn`t necessary,, just cap or tape it off
The red can either go to rc or rh,, you must put a jumper from rh to rc to make them both get low voltage power