Error code reference

Lennox Air Conditioner Error Code E120

There is a delay in the outdoor unit responding to the system.

There is a delay in the outdoor unit responding to the system.

First step from the service manual

Check all wiring connections. Alarm typically clears on its own after unresponsive device responds.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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E120 on my Lennox Air Conditioner

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There is a delay in the outdoor unit responding

From Service Manual 876082, p.14:

1.Check all wiring connections. Alarm typically clears on its own after unresponsive device responds.

2.Measure door lock assembly resistance across the PTC terminals. Expected: ~200 ohms cold, rising sharply once energized.

3.Inspect strike and latch alignment. A warped door or misaligned strike prevents the switch stack from closing in the correct sequence.

Part W10810403

Door lock assembly

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