The C4 error code relates to the thermistor that monitors the temperature of the indoor heat exchanger, or coil. This sensor helps the system manage cooling and heating correctly, and a C4 fault can appear when its reading is open-circuit, short-circuit, or simply out of the expected range.
Because this sensor sits inside the indoor unit and connects back to the control board via a small plug, faults here are often connection-related rather than a sign of a bigger mechanical problem.
Send us the code and a photo of the display, and a Ford & Doonan technician will get back to you. Please don't reset the unit before you take the photo.
(08) 9331 8800