Thermostat does not detect or control whole-home humidifier/dehumidifier
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.
Possible Causes
How to Fix / Troubleshooting
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.
Repair Difficulty
Required Part
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