Lennox Heat Pump Error Code Green OFF / Red FAST Flash

This code indicates a discharge sensor fault. The control board has detected either an open circuit or an out-of-range resistance reading from the discharge line temperature sensor after 90 seconds of run time. The system shuts down because it cannot confirm safe discharge line temperatures without a valid sensor signal. The sensor, its wiring harness, or both will need to be tested and potentially replaced.

No. The discharge sensor monitors the temperature of refrigerant exiting the compressor, and without a valid reading, the system cannot protect the compressor from overheating. Operating the unit in this condition risks compressor damage, which is one of the most expensive repairs on a heat pump. Leave the system off until the fault is resolved.

Repair costs vary depending on whether only the sensor, the harness, or both need replacement, as well as local labor rates. Sensor and harness parts are generally in the range of $20 to $150, and a technician's diagnostic and repair visit typically adds $75 to $200 or more depending on your area. If the fault has caused compressor damage from delayed repair, costs can increase significantly.

Start by measuring the resistance of the discharge temperature sensor and comparing that reading to the values in Table 4 for the unit. If the sensor reads open or out of range, replace the sensor or the harness. Also inspect the wiring harness and connector terminals for damage, corrosion, or loose pins before ordering parts.

A power reset may temporarily clear the fault code, but the code will return once the unit has been running for 90 seconds if the underlying sensor problem has not been corrected. Resetting without repairing the sensor or harness does not fix the fault and can delay a proper diagnosis.