if you look under the dash passenger side near the center ''hump'' you should see a white flap with a cable attached to it. that is the door that directs the air flow over the heater coil. if you activate the heat control lever while looking at the white flap / door you should see it move.
also the cable is the bottom end of the control cable . it is about 20 - 24 inches long and the top is connected to the heater lever.