My Honeywell Thermostat WiFi System via the "C" Wire was working correctly when the "C-WIRE" was hooked to the A/C Unit.

I needed to change the "C" Wire to my Gas heating system instead of the A/C for potential power outage usage in the future. (My backup generator will be used for the heat system not A/C)

ISSUE: When I shut down only the A/C via the Circuit Breaker - The Honeywell Thermostat goes blank. (Which doesn't make any sense since the RH (Power) and C are coming from the heating System.

ONLY when I have both the A/C & Heater Breakers on does the Honeywell Thermostat come on.

What gives ? Did I miss something here ?

With a potential power lose I would have the Gas Furnace powered (via the generator) but as it looks now the Thermostat needs both on for some reason ?

Thoughts: Could the Thermostat be bad ? Could the impedance of the Wire be an issue?

See pictures below

Thermostat connections[Furnace Wire Connection
Voltagetesting Voltage Testingenter image description here

  • What model is your thermostat? Oct 2 '21 at 23:42

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