A C9 error code could indicate a fault with the thermistor that measures the return air temperature entering the indoor unit. This reading helps the system decide how hard to run to reach your set temperature, so a faulty sensor here can stop the unit operating correctly.
The fault can originate at the sensor itself, along its wiring, or in the way the indoor control board interprets the signal it sends.
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