Has the centre console been disturbed? eg Radio out or upgraded?
The ‘three knobs in a box’ assembly below the radio is the brains of the aircon/climate system, including cabin temperature sensor, and if the plug on the back is not properly connected or a wire is damaged, then there can be strange effects.
- If you can get heat out it suggests the hot water is flowing through HVAC unit OK.
- If you can vary the fan speed it suggests blower and its FET control are working.
- Being able to change things suggests the Intake, Mix and Airflow actuators in the HVAC unit are working.
- This leaves just the cabin thermometer living in the three knobs box, and it could even be as simple as a bad connection inside there, such as to the actual temp sensor, or maybe within the temp knob (Servisol Super 10 contact cleaner to the rescue?)
The obvious thing to try is a different known working set of three knobs, make sure you get the Climate Control set if you have CC.
Edit. I was wrong about where the thermometer is. See the photo of the sensor in my later post below.