Amazon Smart Thermostat Open Cooling Call Circuit (Y-Terminal Issue)

Thermostat calls for cooling, but the outdoor AC unit does not start.

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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 Y wire at thermostat, loose Y connection at furnace/air handler control board, broken Y conductor to outdoor unit, failed Y output driver in thermostat.

How to Fix / Troubleshooting

Safety: Turn off power to both the air handler and the outdoor condenser at the breaker.

  • Confirm cooling call: Ensure the thermostat indicates that cooling is ON.
  • Inspect Y at thermostat: Verify the Y wire is properly seated in the Y terminal.
  • Inspect Y at furnace/air handler: Confirm the Y wire is secure on the control board and that the cable to the outdoor unit is intact.
  • Check outdoor disconnect: Make sure the service disconnect near the outdoor unit is inserted and ON.

If wiring and outdoor unit power are good, but the condenser only runs when R and Y are jumpered at the control board, the thermostat’s Y output is likely defective, and the thermostat should be replaced.

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Repair Difficulty

Medium 3/5

Required Part

Amazon Smart Thermostat Main Control Assembly
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