Furnace and AC both operate at the same time!

[DeucesWild]

I know this is a wiring problem, but I have no idea where to start. I'll just toss up what I know, and maybe someone can fill in the blanks.

I have 2 sets of wires. 1 From the thermostat and 1 from the AC unit.

The Thermostat has 4 wires: Red, Green, Blue and White. The AC unit has 2: Red and white.

First off, there is a new thermostat as the old one was broken. I know it's possible that a new one can in fact be broken, but I'm going to assume it works.

Here's what is happening. When I set the thermostat to 'Heat - Auto' Both Heat and AC units kick on (and fan). When I set the thermostat to 'Cool - Auto' Just the fan comes on. Fan appears to operate properly in both 'fan - on' settings.

I don't know anything about furnace parts, but the unit that the wires from the thermostat and AC unit come together in is where I think the problem is. This unit has 5 terminals labled as follows: W G Y on the left, R C on the right.

The 6 wires from the thermostat and AC unit come in as follows:

Thermostat white to W
Thermostat green to G
Thermostat blue to Y
AC unit white to Y
Thermostat red to R
AC unit red to C

I don't know the exact model, but this is a comfortmaker furnace. I think the AC unit is as well, but I'm not on location to confirm.

Thanks in advance for any help.

[Java_Bob]

check this out should make it clearer for you

Thermostat wiring colors and furnace terminal designations repair.

[DeucesWild]

I found that page yesterday actually, and it may as well be written in German.... Made no sense to me at all.