A/C VW Winnebago Rialta on the same chasis as the Full Camper VW Transport mdl

What is your question?

I have spent $850 so far trying to get the a/c to blow cold. I will blow "cool" if the vehicle sets over night or for a few hours, if the A/C is engaged at highway speeds it will blow "cool" air most of the day, if the system is not disengaged. If the system is disengaged it may not produce cool air. Rialtas have an additional evaporator to cool passingers. The air from this source is cooler than the air from the dast outlets even though it is the same system. The system has been evacuated and recharged three times now, the last time was when the expansion valve was replaced at $429 at a VW dealership. Does any one have experience or a suggestion for repairs.