We just moved into our new home. Noticed the A/C went on all day, non-stop even though it was set on auto at 77 degrees. Figured the thermostat was broken, so decided to replace old one with Honeywell 5-2. Mapped it just like the 4-wiring old one, Y-G-W-R. Red wire on old thermostat was wired to Rc, not Rh, so that's what I did. However, I did take out the jumper between Rh and Rc. The fan blows, but the A/C unit is not on. It only blows out room temp air. I put back the jumper and tried, no luck. I connected the red, w/ jumper and connect to Rh, no luck. Could the initial removal of the jumper wire done something to the A/C unit? We tried turn off and on the main circuit. Please help!

The jumper may have caused the problem. Normally you would connect the red wire to "RH with jumper to RC", connect the yellow wire to "Y", connect the green wire to "G" connect the white wire to "W"
Normally with only four wires you need the jumper wire, If they did not have this jumper the only way it could work is if you had two transformers in the system (one in furnace and one in the A/C) in this case one wire would go to "RH" and the red wire to "RC" with the white wire to "W", the yellow to "Y" and possibly the blue to "RH" the only way for you to tell is open up the furnace and look at the wires from the thermostat and see what connects here and then go to the a/c and see what wires go here. If nothing runs it is posible you burnt out the transformer in the a/c when you put jumper in, if some one did this they would have had to put a jumper between the yellow wire and the fan relay in the furnace.
Lets hope this is not the case . Start at the furnace and see what goes where and let us know. Good luck, Mike

Are you aure it wasn't the time out feature? I know with my Honeywell the time delay is almost 10 minutes. Its protection for the compressor.