I just installed a Honeywell RTH221 Thermostat. The old one had a red, green, yellow, and black wires. I installed the black one to the yellow connection. Now the unit runs backwards... heat instead of cooling... cooling instead heating. How should I have connected the wires?

R to red, black to w, green to g, yellow to y. try this and let me know if it works. If not, I will need to know what color wires are hooked to the terminals on the furnace.

I ended up connecting black to yellow, red to red, green to green, and yellow to white. Now everything is working correctly.

Glad you got it going. Good job.

Thanks! I am not sure how I figured it out.