Ok, 22 is too low. You don't want to go below freezing, or you'll ice up the evaporator. Once it becomes a solid block of ice, it blocks the airflow and you get nothing. While you're climate might be a little low in the humidity dept. cooling air always pulls the moisture out of it.

But back to the truck, do you have a specification for the charge amount? You might just be a little low and it shows up when you spin the compressor fast. At any rate, verifying the system charge really needs to be your first step, as everything depends on that being correct.

MV