Center A/C dash vents blow both heat and A/C

[Mark Pifer]

Hi, I'm know this is specific the a 1970 Heater/Air Conditioning system but I believe the c-bodies and b-body systems are similar.
Here is the issue.
I have a 1970 GTX with air conditioning.
It has an unusual problem.
Currently when I run the regular a/c, not the max a/c, the center dash vent blows cold air on the left hand side vent and hot air on the right side vent. This is unique as both vents are tied into one duct which feeds them both coming off the air handler box.
Now a little background.
We replaced the original dual heater core with a new Old Air Products dual core with valve. We did this because on the original core somebody had the valve shunted out and it could not be made to operate again. So we replace the old brass core with a new aluminum core and new valve.
When we select the Max A/C, the two center vents along with the two side vents blowing cold air.
When selecting regular A/C the left side center vent blows cold air and the right side blows hot air. The issue is both left and right vent are supplied by the same center duct.
Everything does works using the heater or defroster.
Has anyone run into this issue? What is hooked up wrong? What did I miss?
Thank you in advance for you help!

 

[live4theking]

Does it have a dual heater core like the one pictured? And a "h" like is pictured below? The purpose of that valve is to let some hot water to flow so the evaporator doesn't freeze up. Maybe it is letting too much flow.

 

[Mark Pifer]

Does it have a dual heater core like the one pictured? And a "h" like is pictured below? The purpose of that valve is to let some hot water to flow so the evaporator doesn't freeze up. Maybe it is letting too much flow. View attachment 645244View attachment 645243

Thank you so much for replying.
Yes, it is a double core. The old air product part looks similar to mopar service book for 1970 b body shown below.
Any thoughts additionally along with valve adjustment?
I ask because wouldn't combined hot and cold air come out of the center vents as warm air since the are fed by the same duct? If it was a a valve issue would not combined warm air come out of all vents including center, right and left vents?
Also, how can two different temperatures come out of the same duct and divide the left and right center vents to have one cold and one hot?

 

[live4theking]

That's about all I know. I'm not sure how it functions completely. You ask good questions.

 

[Mark Pifer]

Thank you.