Error code reference

Lennox Heat Pump Error Code Green SLOW Flash / Red ON

Discharge line temperature fault

Discharge line temperature fault — discharge line temperature exceeded 300°F (148°C); compressor de-energized until temperature drops below 225°F (107°C).

First step from the service manual

Check system charge and airflow. Verify discharge sensor connection and placement.

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 Green SLOW Flash / Red ON.

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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Green SLOW Flash / Red ON on my Lennox Heat Pump

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Discharge line temperature fault — discharge

From Service Manual 976275, p.47:

1.Check system charge and airflow. Verify discharge sensor connection and placement.

2.Inspect the exhaust duct from the unit to the wall cap. A crushed or lint-blocked duct is the most common cause of airflow-related faults.

3.Measure static pressure at the blower housing with the lint screen removed. Expected: ≥ 1.0 in. w.c. in a still-air test.

Part W10861225

Blower wheel and housing

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First step from the service manual

Get the full diagnostic procedure for Green SLOW Flash / Red ON.

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