Error code reference

Lennox Air Conditioner Error Code 3

Unsteady thermostat input

Lennox codes Lennox air conditioner codes

Unsteady thermostat input - intermittent inputs from the room thermostat, most likely a loose connection at the thermostat.

First step from the service manual

Check for loose connections at the thermostat.

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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Unsteady thermostat input - intermittent inputs

From Service Manual 769839, p.51:

1.Check for loose connections at the thermostat.

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 3.

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