I have a 73, non air car. The heater only blows out defrost or floor. Do the dash vents only connect to fresh air ?
Dash vents without A/C ? Maybe someone swapped in a different lower dash. Can you look what the hose is connected to. Are they connected to fresh air intakes from the cowl?
My 74 Comet LDO had the same RH Vent, was connected directly to cowl intake via plastic connector, used push/pull lever that was mounted under dash, only function was fresh outside air and was not connected to plenum. My non a/c heater plenum (box) would only feed defrost for windshield and floor. David