When replacing my old thermostat with a programmable one, I inadvertently touched the wires together. There was a small blue arc and a burning smell. I didn't turn off the power before installing because of the low voltage - lesson learned. Now there appears to be no power to the thermostat. My other a/c unit is still running and is working overtime to cool my house. Do you think I blew a fuse? If so how do I find out and replace it? Please help, it's supposed to hit 100 degrees out here in AZ today. Thanks.

There may be a small 24 volt fuse in the main control for the AC. May be close or even located on the 24 volt control transfomer, which supplies the control voltage for the thermostat. Not one unit is the same, so you will need to open the air handler and look for this fuse/transfomer.

This exact thing happened to me recently: You can fix this problem yourself.. Turn off the main power, open the door panel to your air handler [mine is in the attic], and replace the 24v fuse that is contained within. It took me about an hour to complete as it was summer in Arizona and my air handler door panel had been taped, plus screws needed to be removed. After removing the old fuse, I inspected it and it was indeed burnt. After installing the new fuse, the thermostat and AC worked brilliantly. I saved myself an electrician callout charge and you can do the same with a .18 cent fuse. This is not a difficult process, just don't give up on it and be patient as you work [at least that's what I tell myself].