Upon arrival to system, no heat call, I was shown to a split system with an air handling unit located in the main hallway closet. The homeowner had stated that he recently had the systems thermostat changed out. After the thermostat was changed out, they were having issues being able to run the heat, and when they try to correct the issue, the system would not run altogether. Upon diagnosis, I found the low-voltage control fuse to be blown. Without this fuse, the system will not be able to run at all. Replace the fuse and started the system and cooling mode to verify proper functions. System is operating well in the cooling mode at this time. Cycle the system, through each other mode heating and emergency heating to ensure functions of those as well. Heat is operating very well at this time. Completed for system inspection to ensure the system is operating within range of factory specifications. Spoke to the homeowner about work completed today, as well as the benefits/savings of