Looking for seasoned datsun/nissan mechanic. My 91, the ac only come out the defrost vents. It will not divert to the floor or center vents. The heat does not work. The blower and fan control works fine. It has been changed. I have disassembled the dash and can see the actuators under the heater unit but no clearance to remove them(2). The actuator on the left side of the heater unit that appear to open and close doors to divert the air/heat, is covered with a control box which 2 screws were removed but I'm unable to locate what holds it on at the top. Point me in the right direction or recommend a seasoned mechanic to repair it. Thank you so much.