Lennox
No Cooling Call Output
Thermostat calls for cooling but the air conditioner or heat pump does not start; fan may or may not run.
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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
Open Y1/Y2 wire between thermostat and Lennox control board, Failed Y output in thermostat, Misconfigured cooling stages in thermostat setup, Blown low-voltage fuse due to previous short on Y circuit
How to Fix / Troubleshooting
Safety warning: Turn off power to the indoor unit before working on low-voltage wiring.
- 1. Verify thermostat mode and setpoint:
- Ensure the thermostat is in COOL mode and the setpoint is below room temperature.
- 2. Check Y wiring:
- Inspect Y1 (and Y2 if present) connections at thermostat and Lennox control board.
- Tighten any loose terminals.
- 3. Test cooling from control board:
- With power on, briefly jumper R to Y1 at the control board.
- If the outdoor unit starts, the thermostat or its wiring is at fault.
- 4. Replace thermostat if Y output is defective:
- If wiring is intact and the system runs when jumpered, install a new Lennox thermostat.
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Repair Difficulty
Medium
3/5
Required Part
Lennox Smart Thermostat
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