replaced old thermostat but A/C dont work


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Old 04-20-09, 01:57 AM
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replaced old thermostat but A/C dont work

I had replaced my old honeywell thermostat chronotherm with the honeywell pro4000. The old thermostat had a W,Y,G,RC,RH, and 2 C terminals wired. they were wired as followed:

white = W
white = Y
green = G
red = RC
black = RH
black = C
and RC was jumped with the 2nd C terminal

on the new tsat there was a tab that jumped rc and r so i pulled it because there is a transformer in the attic air handler and a transformer in the furnace. the new tstat has W,Y,G,RC,R,O,B, and 1 C terminal. I wired it as followed:

white = w
white = y
green = g
red = rc
black = r
black = c

i tested the heat and the air conditioning and it worked but than i realized i didnt jump the rc and c like the old tstat so i googled what it was for and saw that someone said it must be the same way it was. so i jumped it but than the A/C didnt work. i put it back the way i had it and still doesnt work. i put the old tstat on and the a/c still didnt even work. Did i blow the transformer in the air handler? i have a bad sense of smell so i couldnt smell much when i checked the transformer and i dont have a voltmeter to check it. please help
 
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Old 04-20-09, 03:57 PM
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Go to your air handler low voltage terminal strip where all you thin low voltage different color wires connect (R,W,Y etc.), and see if you have 24 volts from the Y connection to ground, when you turn the stat to cool. You are supposed to if wires are hooked up right.

It's rather odd you have two white wires and 2 black wires. Did someone run 2 sets of identical colored bundled low voltage wires up to the stat? Do you have the right white wire on the Y terminal?

And did you go outside and make sure that there is not a condensor unit breaker turned off out there? or tripped? or blown? Or a 'disconnect' that is flipped over in an off position?

Did you have the a/c running before you replaced the stat?

WHY did you replace the stat?
 
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Old 04-20-09, 11:55 PM
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i know i have all the right wires with the right contacts. no breakers are off, tripped or blown and dixonnect is in right position. the A/C was running before i changed the stat and it ran after i changed it until i jumped rc and c because i realized on the old stat rc was jumped with a second c. i replaced the stat because it was an old mercury stat and i just wanted a new one, it kind of looked dumb redoing the house and leaving an old tstat on the wall. i took the transformer out of the air handler and it was all brown so i guess it did burn out. i think i did it when i jumped rc and c so i took that jumper out. ill see when i replace the transformer.
 
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Old 04-21-09, 04:37 PM
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You have one tramsformer or two? If one, it must be good because the heat works. If you have a second one, can't you just voltmeter test it?, rather than just change it out? That's the way I like doing things anyway.

If you were to temporary wire back up your old stat (if you still have it) then that may tell you right there if it is the stat or not, and save any hassle.

If you get no further instructive responses from anyone here, specifically about wiring that stat, maybe you could PM Jay, as he is good with that sort of stuff.
 
 

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