Thermostat indicates 'Dehumidifier Error' or cannot control whole-home dehumidifier

Safety first: Turn off power to the air handler and dehumidifier at the breaker before working on wiring.

Steps to troubleshoot:

• 1. Verify wiring: Check that the dehumidifier control wires are connected to the correct DHUM or dehumidification terminals on both the thermostat/interface and the dehumidifier.
• 2. Confirm settings: In the thermostat's installer menu, ensure dehumidification is enabled and the correct control type (on-board vs external) is selected.
• 3. Test dehumidifier manually: If the dehumidifier has a local control panel, try running it independently to confirm it operates.
• 4. Inspect low-voltage circuit: Use a multimeter (if trained) to verify that the thermostat is sending a dehumidification call when humidity is above setpoint.

When to call a professional: If wiring and settings are correct but the dehumidifier does not respond, a technician should inspect the dehumidifier control board and low-voltage circuits.