American Standard
Humidifier Integration / Control Logic Issue
Thermostat fails to control whole-home humidifier even though humidity readings are normal
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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
Humidifier not enabled in installer settings, Incorrect humidity setpoint, Wiring to HUM terminals incorrect, Humidifier power not present
How to Fix / Troubleshooting
Safety: Turn off power to the furnace and humidifier before working on wiring.
- Enable humidifier: In installer settings, ensure the humidifier accessory is enabled and configured for the correct type.
- Set humidity target: Set a realistic humidity target (e.g., 35–45% in winter). If the target is too low, the humidifier may never run.
- Check HUM wiring: Verify that the humidifier solenoid or control relay is wired to the correct HUM or accessory terminals on the furnace board or thermostat, per American Standard diagrams.
- Verify humidifier power: Ensure the humidifier has its required power source (24V or 120V) and that any inline transformer is functioning.
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Repair Difficulty
Medium
3/5
Required Part
Whole-home humidifier and HUM control wiring
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