When I installed the thermostats originally I blew the fuses on the boards because I hadn't shut the power off before replacing the thermostat. I got it running with the AC and it ran all summer with no problem. When the weather cooled down we shut off the units for a few days. When we went to restart the units the fuses blew. We replaced them and got the unit running again, but if I shut off the unit the fuse blows again. The other day we tried to turn on the furnace and the fuses blew again. We replaced them but still can't get the heat to work. As soon as we turn the unit on the fuses blow. I am almost positive that I messed up installing the thermostats. How can I fix this problem?

Take the wires off the stat turn the power on and see if anything blows. If no touch red wire to white wire and see if fuse blows or furnace starts.