Error code reference
Lennox Heat Pump Error Code DS2 OFF / DS1 SLOW Flash
Low pressure fault
Low pressure fault — pressure switch has tripped (1 strike counted).
First step from the service manual
1) Remove any blockages or restrictions from coils and/or fans; check indoor and outdoor fan motor for proper current draws. 2) Check system charge using approach & subcooling temperatures. 3) Check system operating pressures and compare to unit charging charts. 4) Make sure all pressure switches and sensors have secure connections.
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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