Error code reference

Lennox Heat Pump Error Code 9

Option 1 safety device switch opens after compressor runs more than five minutes.

First step from the service manual

Check Option 1 safety device and wiring.

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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Option 1 safety device switch opens after

From Service Manual 979397, p.49:

1.Check Option 1 safety device and wiring.

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 9.

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