Richard J Washington , DC November 20, 2015 The appliance is a through the wall heater/ac unit the problem was that it would cycle on and off properly for ac but not for heat I reasoned that, if the fan and compressor worked, and if I could discern the thermostat's operation by way of a "click" (for AC, but not for heat), the problem was likely the thermostat. When I replaced the thermostat, the problem was resolved. Do-It-Yourself Rating: Repair Time Estimate: 30-60 minutes