Carrier
No Cooling Call Output
Thermostat calls for cooling, but outdoor unit does not start; indoor blower may 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 Y/Y1 wire between thermostat and control board, Failed cooling relay in thermostat, Tripped float switch opening Y circuit, Outdoor unit contactor coil circuit open
How to Fix / Troubleshooting
Safety first: Turn off power to indoor and outdoor units before working on wiring.
- Step 1 – Confirm cooling mode: Ensure thermostat is in Cool mode with setpoint below room temperature.
- Step 2 – Inspect Y/Y1 wiring: At thermostat and control board, verify Y/Y1 wire is secure. At the outdoor unit, check the low-voltage connections to the contactor coil.
- Step 3 – Check float switch: Look for a condensate float switch in the drain line. If tripped due to a clogged drain, clear the drain and reset the switch.
- Step 4 – Bypass thermostat (advanced): With power off, jumper R to Y at the control board. Restore power; if the outdoor unit starts, the thermostat or its wiring is at fault.
- When to call a pro: If the outdoor unit still does not start, a technician should test the contactor, capacitor, and compressor circuits.
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Repair Difficulty
Medium
3/5
Required Part
Carrier Smart Thermostat
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