Error code reference

Lennox Heat Pump Error Code 8

Welded Contactor

Welded Contactor – Compressor always runs; contactor failed to open or thermostat demand signal not connected to module.

First step from the service manual

Check compressor contactor for failure to open. Verify thermostat demand signal is connected to module.

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
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Welded Contactor – Compressor always runs

From Service Manual 979398, p.50:

1.Check compressor contactor for failure to open. Verify thermostat demand signal is connected to module.

2.Measure control board supply voltage at the test points. Expected: 12 VDC and 5 VDC; a drop below 4.75 VDC on the logic rail points to a failed onboard regulator.

3.Inspect all connectors on the main control for corrosion, thermal stress, or backed-out pins. Reseat each connector with the power disconnected.

Part WPW10804018

Electronic control board

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First step from the service manual

Get the full diagnostic procedure for 8.

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