The "THRIFT AIR HEATER" has a single knob. Pull the knob out to open a door in the heater assembly, and turn the knob clockwise to turn on the blower motor. There should be three speeds for the blower fan. There also is a lever for "HEAT" and "DEFROST" on the heater assembly below the dash on the passenger side.
Most of the 1960-1966 trucks have this type of heater.
