We installed a Honeywell RTH6400 thermostat in January. We now need a/c & outside unit will not come on, inside unit runs. When we installed this we thought everything was hooked up right, but who knows. We've pulled the cover off the thermostat & we have a blue wire that is taped, should it be hooked up to something? Is this a different issue all together?

Do you have a jumper wire between rh and rc?

Metal jumper wire is connected to R & Rc.

Do you have a volt meter?

No, My father does, but not here. I just looked & the red wire is on Rc. Is this correct?

Yes as long as it has a jumper. Set the t-stat so the ac should come one. Then go outside and take the 2 screws holding the panel to the electric on the ac. Right where the power goes in. look for this contactor.

http://yueqing-shi-shinaidi-electrical.tradenote.net/images/users/000/102/716/products_images/283101.jpg

See if the two bottons in the middle are pushed in.

Did you check the breaker to the outdoor unit?

Checking will be right back.

Rember that is 220 volts so be careful you can push those buttons with a screw driver.

Not finding where the power goes in.

We reset breaker to unit earlier & no success.

Should be on the back left or the back right of the unit closest to the house.

Already tried resetting the breaker..

Is it a the entire back of the unit?

Not sure, what brand do you have?

Lennox

Yes some lennox and trane units you have to take the entire pannel off.

Ok, will do

There is only 1 black button & it seems to be pushed in

OK if it is pushed in then your t-stat is working corectly. Your problem is with your main power. 220 volt. Is there a outside disconnect for the main power on your house?

http://www.homeairdirect.com/store/images/disconnect.jpg

My husband says that if he pushed the button in, the outside fan works, but if he takes the screw driver off, then it goes off.

OK then the problem is with the t-stat wires.

See if he can find where they go into the unit. They will be buged together with the two small wires that go up to each side of the contactor, usually blue

Any idea what we should do? I have a blue wire that is not connected to anything.

Blue wire on the thermostat isn't hooked up to anything.

Sorry I confused you. I did not mean at the t-stat. there should be 1 t-stat wire outside and it should have a red and a white in it and out there is where they should be buged to the two blues. Make sure that connection is good.

Everything seems to be connected OK outside

OK then there should be no problem there. Take your stat back off and with a jumper wire or a pair of needle nose pliers touch between
r-y and see if the ac comes on.

Outside? Sorry trying to relay message to my husband

No in at the t-stat

Take it back off the wall and jump between r and y