P3
Carrier
Low Outdoor Ambient Protection / Compressor Low-Temperature Protection
Indoor unit displays P3 and system may not start in heating or may shut down
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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
Outdoor temperature below operating range, Faulty outdoor ambient sensor, Control board misreading temperature, Incorrect system configuration
How to Fix / Troubleshooting
Safety: Turn OFF power before accessing outdoor components.
- Step 1 – Check outdoor temperature: Compare actual outdoor temperature to the Carrier unit's minimum operating temperature in the manual. If below spec, the unit may be protecting itself.
- Step 2 – Inspect ambient sensor: Ensure the outdoor ambient sensor is correctly mounted and not influenced by exhaust vents or direct sunlight.
- Step 3 – Power reset: Turn OFF power for 5–10 minutes, then restore and test.
- Step 4 – Technician diagnosis: If P3 persists in normal temperatures, a technician should test the ambient sensor and outdoor PCB.
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Repair Difficulty
Medium
3/5
Required Part
Outdoor Ambient Temperature Sensor
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