D001
GLAS
Dehumidification Control Output Fault
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 GLAS DEHUM or ACC terminal, Incorrect dehumidification configuration in GLAS, Loose or open dehumidifier control wiring, Failed dehumidification relay on GLAS main board
How to Fix / Troubleshooting
Safety warning: Turn off power to HVAC equipment and any standalone dehumidifier at the breakers before working on wiring.
- Step 1 – Verify wiring: Confirm dehumidifier control wires are correctly connected to GLAS accessory terminals and to the dehumidifier or furnace board as specified in the GLAS manual.
- Step 2 – Check settings: In GLAS settings, ensure dehumidification is enabled and configured for either dedicated dehumidifier or AC over‑cooling.
- Step 3 – Continuity test: With power off, test continuity of the dehumidifier control wires.
- Step 4 – Bypass test: With power on and 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 wiring and configuration are correct and the accessory responds to a manual jumper but not to GLAS, the dehumidification relay on the GLAS main board is 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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