Y001
GLAS
Open Y (Cool Call) Circuit
Thermostat shows Y001 and will not start the air conditioner when cooling is demanded.
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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
Loose or broken Y wire at GLAS wall plate, Disconnected Y terminal at furnace/air‑handler control board, Open thermostat cable conductor for Y, Failed Y relay output on GLAS main board
How to Fix / Troubleshooting
Safety warning: Turn off power to both the furnace/air‑handler and outdoor condenser at their breakers before opening panels.
- Step 1 – Check GLAS Y terminal: Remove the thermostat and verify the Y (or Y1) wire is fully inserted and clamped.
- Step 2 – Check furnace/air‑handler board: With power off, confirm the Y wire is connected to the Y terminal and secure.
- Step 3 – Continuity test: With power off, disconnect Y at both ends and test continuity with a multimeter. Replace cable if open.
- Step 4 – Bypass test: With power on and caution, briefly jumper R to Y at the furnace control board. If the outdoor unit starts, the AC system and control board are functional.
- Step 5 – Suspect GLAS relay: If the AC runs with an R‑Y jumper but not when GLAS calls for cool, the Y 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 (Y Cool Relay)
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