Came out to call for a system not heating properly. Customer stated that he was changing out his thermostat from the OG&E stat to a simpler thermostat. He had problems with the new thermostat not operating and blew a fuse. Customer had a friend stop by to help him install it and still wasn’t working properly. I checked the thermostat over and found the common wire on B. Switched it to C terminal for common. Customer had replaced the fuse in board already, so I tested the thermostat and it wasn’t kicking the system on still bypassed the thermostat and the system worked. There’s a good chance the customer shorted the thermostat or it was bad out of the box. Customer approved me installing a Honeywell T6 thermostat after we discussed pricing. I took existing thermostat off the wall and installed the T6. Wired thermostat correctly and tested operation of Heat and AC. System is now operating properly.