One day while parked with the engine idling in front of a friends house; the entire front end of the car was enveloped in a big white cloud. Upon inspection we found no water puddles or other evidence of radiator/water pump/hose leaking. The overflow reservoir was down some but not empty. My Volvo mechanic charged me to install a new cap for the reservoir. I don't think that is what caused the cloud. My air conditioning still pushes out some cool air but it is no longer cold. My question: "Is there some sort of relief valve for the air conditioning"? I had the air conditiong system checked for leaks (free) and was told there are no leaks. My R-134 conversion was done about 4 years ago). Thank You