I've got a problem with my heater only producing warm air- Heater core has been changed recently, and heater tap seems to work (Heater core and brass pipes get hot) I've got a feeling my Air mix door is faulty/broken, not closing correctly. With the car at operating temp and the brass pipes on the heater core hot. I have removed the Air Mix motor and operated the flap via the cog to full open and closed. full closed delivers cool are, and full open delivers warm. But I can't seem to get Hot air. Is there any way to physically view this part without removal of the entire dash. Or is it a whole dash out, and open the heater box to find out?