[masraum]

Originally Posted by rick-l

This?
http://customer.honeywell.com/techlit/pdf/PackedLit/69-0780.pdf

Look at page 2 where it says thermostat.

Red = one side of transformer, 24 volts AC
White = call for heat
Yellow = cooling
Green = run fan all the time


Black or the common terminal, the other side of the transformer, not typically run to the thermostat. You need to find out what they are doing with it.

Yep, but look at Figure 2. That shows 2 leads coming off of C.

I think more and more thermostats are coming these days that can take advantage of C because there are wifi thermostats and programmable thermostats with memory and that sort of thing that take power to run. Most will also use batteries (like my current thermostat) but can take advantage of C if it is available.