There are two heater/defroster systems available on your '65 Chevy C20...Thrift-Air (single pull knob/2-speed) or Deluxe-Air (three levers/3-speed). On the Thrift-Air system, the defrost is activated by flipping the lever on the under-dash distribution box. The heat/defrost is controlled, via the 3-lever dash control on the Thrift-Air system.
