Carrier AC Error Codes and Troubleshooting Carrier Error Codes 08 defrost mode 1 0A Defrost Mode 2 F0 low charge or refrigeration system interruption F3 Outdoor Ambient Temp. Sensor Malfunction F4 outdoor mid-coil Temp. sensor malfunction F5 outdoor discharge air Temp. sensor F7 cooling oil return cycle E1 System High Pressure Protection E2 Indoor Freeze