Ok, kind of a long story here. My dog chewed the thermostat wire out of the outside central air unit. I replaced the wire between the unit and the house, fine, worked, no problem. He did it a 2nd time. First, I built a fence around the unit, then I replaced the wire again. This time, nothing. I double checked and triple checked the connections and they're fine. I checked the breakers. Just for the hell of it, I replaced the contactor. Still nothing. If I press in the contactor, it works fine, if I want to sit there and hold it in. Furnace will not kick on either. I traced the thermostat line from the a/c unit under the house to the point that it goes up through the floor. It looks fine, no visible marks on it, all conncections look good. The thermostat is about 6 months old, digital. When I turn it on it clicks as if it is working fine. I am at a loss. Please help!

Check your transformer for 24V on low voltage side

Ummm... And how do I do that?

Open up the access panel for the air filters. You should be able to see the thermostat wires connecting to a circuit board. You can check for 24 volts between the R and com terminals with a voltmeter , test light, or a voltage detector. If you don't have power there, or perhaps skip checking the voltage, and look for an automotive style blade fuse on the circuit board.

My dog ate the insulation off the vapor tube and was chewing the flex on the 230 volt line.

http://www.photolocker.net/images/Labman/KatetheAC.jpg

Thanks! And cute dog! Thankfully neither of our dogs have been electrocuted!

It's just 24 volts in the wire when it is running the A/C kind of like putting you tongue on a 9Volt battery for a dog, maybe he likes it, just kidding. Labman is probably right, the transformer or a low voltage fuse, there could also be a fuse in the thermostat, mostly just digital stats have this one.