Both heat and A/C come out of dash A/C center vents

[Pop]

Hi, I'm know this is specific the a 1970 Heater/Air Conditioning system but I believe the e-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!

 

[cuda joe]

there are a bunch of doors that open and close in the heater box for different heater and ac control settings all controlled by vacuum first make sure you have vacuum .. then check all the vacuum diaphragms on the heater box they usually have a normal position when it has one vacuum line to it not 2 ..when vacuum is applied they will open or close the door to check apply vacuum to each directly if they have 2 lines to the diaphragm one is to open the door the other is to close the door i hope this helps

 

[Pop]

Thank you!