Greg, the purpose of that extra door was not to allow fresh air into the cab from the outside. It was for converting the fresh air heater into a recirculating heater. Pulling the cable knob opened the tall, narrow door while at the same time, an unseen door blocked off the hole in the inner cowl where the fresh air normally comes in. So that means that the tall, narrow door was actually an intake for bringing in air from the inside of the cab and recirculating it through the heater. At least that's the way I think it works. I have been wrong before (earlier today
).
Carl
