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.