My 54 gmc came with a deluxe heater and when I got the truck it looked to difficult to get it to function so I put a round type heater in and it has been good .I took the deluxe heater off the shelf yesterday and took it apart to clean it up and noticed on mine has a cable that closes a door allowing the air in from outside the vent in the cab .Most ones I see on the net don’t have this door but has a cable that goes to defrost or heat we’re mine is controlled by a lever anyone know what the difference is .here are the two types ,found on Deves site. The blue one is the style I have .
