E290
Lennox
Dehumidification Control Error
Thermostat displays E290 indicating dehumidification control fault; dehumidify function does not operate correctly.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect dehumidification wiring between thermostat and Lennox furnace/air handler, Misconfigured dehumidification mode in thermostat setup, Failed dehumidification relay on Lennox control board, Open or shorted DHUM or D terminal wiring
How to Fix / Troubleshooting
Safety warning: Turn off power to the indoor unit before adjusting wiring.
- 1. Verify dehumidification configuration:
- In the thermostat installer menu, confirm the dehumidification type (overcooling, blower speed reduction, dedicated dehumidifier) matches the Lennox equipment.
- 2. Inspect DHUM/D wiring:
- At the Lennox control board, check the dehumidification terminal (often DHUM or D).
- Ensure the wire from the thermostat is secure and not shorted.
- 3. Test dehumidification function:
- Command dehumidification from the thermostat and observe if the blower speed or compressor operation changes as expected.
- 4. If E290 persists:
- The dehumidification relay or control circuit on the Lennox board may be defective and require replacement.
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Repair Difficulty
Medium
3/5
Required Part
Lennox Furnace/Air Handler Control Board
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