Honeywell Digital Thermostat with autoswitchover

[JBinOR]

Here's a mod I did this winter. I really wanted a thermostat that would automatically switch from Heat to A/C. I used a Honeywell RTH5100B thermostat. I had to look through the manual to figure out how to activate the switchover feature, but one's that's done, it does not need to be done again. Wired like I did, the fan kicks on only when the fan is set to ON, not when set to AUTO.

The red wire is the 12V DC+, yellow is A/C, white is furnace, gray is low speed fan. I believe that blue is the hi speed fan and green is the 12V DC-.

Red wire to R, Yellow to Y, White to W, Gray to G.

[JBinOR]

Maybe it was. I did it a while ago, and those were the two wires I didn't use.

[Altern]

:h hmm strange -- With residential T-stats the green = fan and blu/blk = common.