The Thrift Air heater and the Deluxe heater have different dash controls, different underdash diffuser box, different control cables and different fan motor speeds.
The Thrift Air heater is a two speed fan with a single pull knob on the dash. The defrost must be engaged by shifting the lever on the underdash diffuser box. The Deluxe Air heater/defroster has four levers ('60-'63) and three knobs ('64-'66) on the dash. The heater, fan speed and defroster are controlled at the dash controller.
I hope this helps.
Tony
