random aircon problem

[too jazzy]

hey guys got a problem with the air-con, when its set to blow air at the face, and when the car goes up a slight hill the air will automatically cut out to the face and blow straight at the windscreen, or when on the highway at above 90 then it will also cut off and go straight to the windscreen in that case you have to slow down and then it will change by itself back to the face.

just wondering what could be the cause of this?

[bcw61]

This is the classic symptom of a vacuum leak within the HVAC vacuum controller system.

Do a search through the JC forums, as there are quite a few threads previously raised for this exact same issue - together with various fault-finding steps & fixes.