Hello I would like to help you with this.
From what you described you may have a problem with your EATC control which distributes the vacuum to the different sections of your air conditioning unit to control where the air is being distributed to.
Please see diagrams below which show the vacuum routing and connections as well as a troubleshooting chart.
I hope this helps you,
Please let me know if I can help further, and please remember to indicate that I have helped you today by pressing the accept button.
you need to check the connection number 5 for the vacuum hose which is the vacuum supply and make sure you have good engine vacuum at that point.
If you do not have vacuum that the point please check the check valve item number 16 and make sure that it is functioning. It should allow vacuum to be pull through it but not the other direction it could be blocked and not allowing backing to the EATC.
If you get vacuum into connection 5 on the EATC then it should distribute the vacuum to the appropriate output ports on the EATC for it to operate the vent controls.
If you have a good vacuum source at this connection and it is not distributing the vacuum only outputs 1,2,3,4 According to their proper function then the EATC needs to be replaced