I have a White Rodgers 1F78 thermostat. The guy who installed it for me installed it incorrectly at the time, and could only get the heater working, when summer came along, I had to rewire the stat to get the a/c to work, now it's getting colder again and when I turn on the heater, it doesn't kick on. I have 4 wires coming out of the wall, Red hooked to RC(which is jumped to RH), White hooked to W, Green hooked to G, and Blue hooked to Y. These colors coincide with the heater connections as well, so all wires match on both ends. When I switch on the heat, I hear the stat click after a few seconds, and then nothing else happens. The heater never does anything, but if I turn on the ac, it kicks on just fine. Don't know if there is a pilot that has to be lit or not, it's a pretty old LOOKING heater. Singer model ACF19-24-1. And I also checked my circuit breaker, it's not tripped, reset it anyway just to play it safe. Any help would be great before I have to pay an HVAC guy to fix something stupid. Keep in mind, it worked fine with the wrong wiring scheme last winter.

There isn't enough info to give a bulletproof answer here. First off, I did not research that tstat. No time. So I assume you know enough to follow what I say below.

First off, is the thermostat wiring done correctly down at the furnace and/or AC control panel? That must be correct for things at the tstat to work correctly.

Is this a dual system with two transformers, one in the heat unit and one in the AC system? If so, you need more conductors coming to your thermostat. Four isn't enough. You need at least 5 if your tstat is self powered or 6 for the cooling system to power it (using the C terminal).

Is this a combination furnace/AC system all controlled by one control board? If so, it should work as wired if your tstat is powered by batteries.

Really, you could just put it back to last winter's wiring and deal with it until you get your service man out to do a PM. He'll know what to do.

After writing all this and proofing it, it occurred to me to ask this. What WAS the wiring that worked for heating? If I know what you changed and how it is hooked up for each season I could probably get a handle on what needs to be done.

EPM

I have some trouble shooting ideas for you to try.

On the circuit board at the furnace short between the R terminal and G terminal this should make the blower motor come on.

If that works do the same with the R terminal and the W terminal, depending on what furnace you have, this should make your draft assist motor come on or it should atempt to light the pilot if it has one.

If this does not work do the same with the R terminal and the Y terminal, this should make your out door unit run, and if it does that means that you are getting 24 volts out of the transformer. If it does not run it could be a bad transformer or you are not getting power to the transformer. So feel of the transformer to see if it is warm if it is warm it should be working.

Let me know what you find out.