Air Conditioner problems of the 1996 Volvo 850

At 49,706 miles the dealer replaced the air conditioner evaporator under warrenty. Approximately 32,000 miles later it had to be replaced again at a cost of approximately $800. Approximately 36,000 miles later it now needs to be replaced again. The dealer estimated the work would cost $800. We live in a climate where the a. C. Is used only in summers. The car is serviced regularly at a Volvo dealership and the car is garaged. Both the dealer and the manufacturer refused to make any concessions siting the current mileage and the fact that the parts are no longer under warrenty. I feel the system continues to be defective, was never fixed properly and Volvo should accept some monetary responsibility to make it right. Air conditioning systems should not have to be replaced three times in 125,000 miles.