Carrier F3

What does Carrier F3 mean?

The control has detected a fault in the outdoor ambient temperature sensor. Carrier's repair method is to measure the resistance value in the sensor, since the system uses outdoor temperature to manage operation. A reading outside the expected range triggers F3 and stops normal running.

Symptoms

• F3 shown on the indoor unit display
• Outdoor-temperature-based control affected
• System will not run normally
• Fault isolated to the outdoor ambient sensor

Common causes

• Faulty outdoor ambient temperature sensor
• Sensor resistance outside specification
• Open or shorted sensor wiring
• Loose connection at the outdoor board

Diagnostic steps

1. 01

   Confirm the F3 code

   Verify F3 on the indoor unit display, which reports faults for both units.

2. 02

   Measure the sensor resistance

   Follow the manual and measure the resistance value in the outdoor ambient temperature sensor.

3. 03

   Compare to the resistance chart

   Check the reading against the manufacturer's resistance-versus-temperature data.

4. 04

   Replace if out of range

   If the sensor reads out of spec, replace it and confirm the code clears.

When to call a professional

The outdoor ambient sensor sits inside the outdoor unit near live electrical and refrigerant components. If you are not comfortable opening the unit and measuring sensor resistance safely, have a licensed HVAC technician test and replace it. A professional can verify whether the sensor, its wiring, or the outdoor board is the source of the F3 fault.