A/C air flow on 1995 Dodge, 5.9 Diesel

It appears that the air flow through the vent begins to slow down after system is on for a while. I would then run the blower without the A/C, and then in a few minutes the air flow would come back. To me it seems the evaporator freezes up and blocks the air flow. Once the A/C is turned off, the air flow slowly returns to the speed setting on the fan switch.The system was recharged after extensive cab off body work. I did use a vacuum pump to see if there is a vacuum leak in any of the vent positions. Every position held the vacuum. The vehicle vacuum pump maintains 26 inches of vacuum when running. Any help would be appreciated.

Chuck, when switching from A/C to vent is the internal airflow versus outside airflow manually or automatically switched? It could be that this switch is malfunctioning. Outside airflow could be flowing freely but the internal airflow may be blocked or not completely switching.

I have tested the vacuum system for the vent system. Everything worked properly. I have reason to believe that it has something to do with the wiring to the heater electrical switches. The system was not working properly. I replaced the factory stereo from an auto wrecker and the ventilation started working properly. Then I had issues with the stereo, tugged somewhat on the wiring, which I think has the heater wiring in the harness, the ventilation system acted up again. A few weeks later I was preparing to replace the ventilation controls, I road tested the system to check if it was working. To my surprise, the ventilation system was working. I am at a loss. I guess I should be glad it works. Thanks for your input.

After an exhaustive effort to figure this out, I decided to put dielectric silicone on the three firewall connectors and A/C pressure switches. Since doing that, the A/C system is working properly. I am going to guess that there was a poor connection in one of these connectors. I am glad it is fixed.

Thanks for the update Chuck!
This info will be a huge help to someone with a similar problem!