[Ryguy]

I bought a new thermostat tonight, a honeywell CT87B, I unhooked the wires from the old stat, and now have no idea what there all for or where they go. I have a carrier central air unit, and an older sears hot water baseboard heat unit, I have two sets of wires coming from the wall. There first one has two wires, Red and White which I am assuming is heat. The second has 4 wires, red, white, blue, and green which I am assuming are the AC wires. Where do I need to connect all these? I connected them as they were on my old thermostat but the AC didn't turn on. The terminals on the back of the thermostat are Rh Rc W Y G.

Can anyone help me out before we freeze :) It's snowing outside and awful cold.

Thanks in advance

[labman]

Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

None of your wires are yellow. You need to check at the air handler or A/C compressor outside which wire is connected to the Y terminal or compressor relay coil. I would connect the red/white pair to RH and W, In the second bundle, red to RC, green to G, and once you identify it, the A/c wire to the Y. Likely the blue connects to the A/C coil too, so that just leaves the white.

[Ryguy]

So the blue and the AC (should be yellow) wire would connect to the same terminal? Which would be the Y on the thermostat? I do not have any yellow wires, I will have to go outside tomorrow and look at the AC unit to see if the white connects to the coil.

I did manage to get the heat working while waiting for a reply, you were right that was the first bundle with the red and white wires.

And again thanks for the reply!!

[Ryguy]

I got it!! Your right the white wire is supposed to be yellow, ( looking at the old thermostat) The white and the blue were connected together on the Y terminal, And the little red wire goes to Rc like you said, now the fan works, the ac kicks on and the heat works.

Thanks for the help!! I really appreciate it!!