A/C anatomy question for experts

[dhillman]

Hi board. I am in the process of dismantling the ACC air delivery system inside my 350SD-1991, chasis # 126134. I already removed the dash. I found the air/recirculation vacumm elements were not working as well as the diverter flap element. I removed the upper cover of the housing where the rubber piece attaches to the center air outlets of the dash. I found there is a communication from the evaporator side to the heater side at the top of that cover area. This means that no matter how hot is the heater core the air will by-pass the core by going up and then through the center outlet. My anatomy question is: Is there suppose to be a barrier between the top of the heater core and the cover of the heater housing? I can see ther was some type of foam at the top of the heater core, (no longer there). If there is no barrier at this place, how can you control the air flow at the center of the housing. How can you get the air to go through the hater core to be distributed to the cabin? The symptom I was having was no heat even at maximum red area in the temperature wheel.

Please help me to identify how the cold (evaporator) and Hot (heat exchanger) mix together.

Thank you in advanced

Darrel.