Any idea what the cause of this could be?
The head gasket had previously gone on this vehicle letting oil into the coolant - I was thinking the coolant/air heat exchanger could have an oil film stopping any heat getting through but now think the oil would transfer heat as well so maybe it;s not that.
Maybe an air lock? - but it transfers no heat at all as far as I can tell... so unless there's no water in the matrix at all.... which is unlikely?
I'm starting to think it is more to do with the mixer dial on the dash
- perhaps the mixer flap that mixes the hot and cold air is stuck? The dial turns normally though.
Any ideas?