H3
Carrier
Humidistat / Humidity Control Fault
Carrier thermostat or humidifier control shows H3; humidifier runs continuously or not at all regardless of humidity setting.
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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
Failed built-in humidistat in Carrier control, Miswired external humidistat, Shorted or open humidistat wiring, Control board logic failure
How to Fix / Troubleshooting
Safety first: Turn off power to the HVAC system before working on control wiring.
Steps:
- 1. Verify settings: Check the humidity setpoint on the Carrier thermostat or humidifier control. Ensure it is not set to OFF or 0%.
- 2. Inspect wiring: If an external humidistat is used, verify correct wiring between the humidistat and furnace HUM terminals or humidifier control. Look for shorts between wires.
- 3. Bypass test (for external humidistat): With power off, temporarily jumper the humidistat terminals at the furnace or control. Restore power and see if the humidifier operates. If it does, the humidistat is likely faulty.
- 4. Replace humidistat or control: Install a new Carrier-compatible humidistat or replace the integrated control if it is not responding correctly.
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Repair Difficulty
Medium
3/5
Required Part
Humidistat / Humidity Control
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