There was no power to the thermostat. I found in the attic the homeowner had shut the power switch off believing it was a light switch. I checked over the unit to find the intermittent power loss issue. I found the three amp fuse was partially installed, and the connectors were loose. I tightened the terminal connections and installed the fuse. I checked the connection box in the furnace and the disconnect switch and found no wiring issues at the condenser. The wires are properly connected and the breaker was tight. I showed the homeowner how to link his thermostat to the app. The unit is operating properly at this time.