'88 300SEL air conditioning problem
 

car seems to be blowing about half cool. I put thermometer in center outlets and just barely get 65 degrees. I can feel some cool air as though it is introducing outside air along with the cooling . Could this be a monon valve problem and if so what is the solution? The system appears to have a full charge.Thanks for any input . Pauljc

What leads you to believe the system has a full charge? Have you hooked up a manifold gauge and measured high and low side pressures? You cannot go by sight glass alone, especially if it is a converted R134a system.