Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees....
I think we have a capacity problem here......really unknown how much refrigerent is in the system, since we have guys adding 1/2 cans...only accurate way to add freon is recover and evac the system, then add freon by weight......