I bought a Honeywell rth221b thermostat. I was smart enough NOT to mark the wires when I took off the old one.:mad: the wires that come out of the wall are red, green, white, and blue. The thermostat looks like this-

Y-o o-Rh
G-o o-Rc
o-W

Im assuming green to G, red to Rh (Rh and Rc have a jumper between) and white to W. Where in the world does blue go?? My heat worked but not my central air. Im assuming the A/C is the blue wire?

Like a typical guy, I threw away the instructions months ago and never checked to see if the AC worked... Smart... I know.

Thank you in advance for your help and tips.

Blue has to be (Outside unit - Y) especially if manual fan works because that is G. In AC mode the thermostat controls the fan.

You might want to print this out after reviewing it. https://www.askmehelpdesk.com/heatin...eat-58313.html I am thinking blue to yellow but read the whole thread.

I also say blue wire to Y terminal. Here are your instructions.

THANKS for the answers! Almost there!

This is what's on my furnace. How do I know if my AC unit has a transformer? I don't know if I should use the jumper.

Hope this is helpful!

Need a jumper between rh and rc... blue goes to y terminal...

This looks bit odd to me. I see the blue wire going to the yellow terminatal but I also see another red going to the same terminal. I think it goes to the one vacant terminal marked G, what do you think KISS?

Looks to me like the whitish-yellow and the red are the ones used to go outside to the ac unit,, this is OK rutterback

Nothing is working... this is what my thermostat looks like... thanks again for everyone's patience.

Which one should I try in the "G"?

Thank you

Move the red off the yellow leaving the blue still connected to yellow. Move red to the empty G on the right.

I think we need to start completely over. This looks way to simple and it should be working. Hah.

I propose - disconnect the thermostat.

We are going to "play thermostat". So before trying things disconnect power. Can I assume that you don't have a voltmeter? Leave the wires attached because they are disconnected at the other end. Just add the jumpers.

Jump R to Y and Gc at the furnace. Turn on furnace. Outside unit and fan should come on. Might have to wait 2-5 minutes. Fan will come on immediately.

Turn off power. Remove these jumpers.

Jump R to W. Turn on power. Furnace should comeon and a short time later, the furnace fan should come on.

Turn off furnace. Remove jumpers.

That checks out the furnace.

DO the tests and report back.

Check the fuse near your circuit board or maybe you blew the transformer.
You did turn the power off before playing with wires on tstat didn't you?

Nothing is working! Please help!! Its 95 outside!

I never shut the power off like an idiot. I don't know if there is a voltmeter either? I'm going to try what KISS said... ill report back.. thank you

I never did understand siberairs comment and reddie to me. He said I was wrong but never explained further. I have not seen a board on the furnace with 2 wires going to it. The blue/yellow sends the signal, the second red should be jumpered at the stat.

This may amuse you but I see that Siberianair has been blocked out as a troll. Maybe skip his suggestions for now.

Rutterback--- what did you ever do to solve the problem? I'm having the same issue!