Error code reference
Lennox Heat Pump Error Code Green OFF / Red FAST Flash
Discharge sensor fault
Discharge sensor fault — board detects open sensor or out-of-temperature sensor range after 90 seconds of run time.
First step from the service manual
Check discharge sensor resistance per Table 4. Replace sensor harness if open or out of range.
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
- Verified part numbers when replacement is required
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