carrier fault code

I have been blowing the 3 amp fuse when my ac is turned on. It runs fine with the heat on. The fault code is for a short in the 24v wiring. I checked my ac unit outside and couldnt find and shorts. I also installed a new thermostat this winter so i double checked the wires going into it and they all seem to be correct. Thanks in advance for your help it has been 88 degrees the last 2 days here in cincinnati and getting a little toasty...:furious: