Thermostat does not detect or control whole-home humidifier/dehumidifier

Safety first: Turn off power to the furnace/air handler and any standalone humidifier/dehumidifier units at their breakers before working on wiring.

Steps to troubleshoot:

• 1. Verify accessory type: Confirm whether your humidifier/dehumidifier is 24VAC control or line-voltage and ensure it is compatible with the Emerson thermostat’s accessory output.
• 2. Check wiring: At the furnace board or accessory, verify that the control wires are connected to the correct HUM, DH, or accessory terminals as specified in the Emerson installation guide.
• 3. Enable accessory control: In installer setup, enable humidification or dehumidification control and set appropriate humidity setpoints.
• 4. Test accessory independently (advanced): With power off, temporarily jumper the accessory’s control terminals to simulate a call and verify it operates.
• 5. Replace thermostat if relay is faulty: If wiring and configuration are correct but the accessory never receives a control signal, the thermostat’s accessory relay may be defective.

When to call a professional: Accessory wiring and voltage compatibility should be verified by an HVAC technician to avoid equipment damage.