Error code reference
Lennox Heat Pump Error Code 3
Unsteady thermostat input indicating intermittent inputs from the room thermostat, most likely a loose…
Unsteady thermostat input indicating intermittent inputs from the room thermostat, most likely a loose connection at the thermostat.
First step from the service manual
Check for loose connections at the thermostat.
The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.
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- Step-by-step tests with expected resistance, voltage, and continuity values
- Wiring diagram references and connector pinouts from the OEM service manual
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