D001
GLAS
Dehumidification Control Output Fault
The thermostat displays D001 and will not activate the dehumidifier or over-cooling function when humidity is high.
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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
Dehumidifier not wired to the GLAS DEHUM or ACC terminal, incorrect dehumidification configuration in the GLAS, loose or open dehumidifier control wiring, failed dehumidification relay on the GLAS main board
How to Fix / Troubleshooting
Safety warning: Turn off the power to the HVAC equipment and any standalone dehumidifier at the breakers before working on the wiring.
- Step 1 – Verify wiring: Confirm that the dehumidifier control wires are correctly connected to the GLAS accessory terminals and to the dehumidifier or furnace board as specified in the GLAS manual.
- Step 2 – Check settings: In the GLAS settings, ensure that dehumidification is enabled and configured for either a dedicated dehumidifier or AC over-cooling.
- Step 3 – Continuity test: With the power off, test the continuity of the dehumidifier control wires.
- Step 4 – Bypass test: With the power on and using caution, manually jumper the dehumidifier control terminals at the furnace board or dehumidifier. If the unit starts, the accessory is functional.
- Step 5 – Replace thermostat: If the wiring and configuration are correct and the accessory responds to a manual jumper but not to the GLAS, the dehumidification relay on the GLAS main board has likely failed. Replace the thermostat.
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Repair Difficulty
Hard
4/5
Required Part
GLAS Main Control Board (Dehumidifier Relay)
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