Error code reference
Lennox Hvac Error Code 301
The O relay on the air-handler has failed (pilot relay contacts did not close or relay coil did not energize).
The O relay on the air-handler has failed (pilot relay contacts did not close or relay coil did not energize).
First step from the service manual
Replace control. The alarm clears after a reset.
The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.
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Get the full diagnostic procedure for 301.
- Step-by-step tests with expected resistance, voltage, and continuity values
- Wiring diagram references and connector pinouts from the OEM service manual
- Verified part numbers when replacement is required
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