420 benz, you found R-12 at Pep Boys?? I gotta check out my local one tomorrow. Don't quote me on this one but I was talking to the youth minister where my kids go to evening church, he said he has been a heating and air man for 15 years, including cars and told me that the large hose is usually the low pressure side and the smaller diameter hose is the high side. But he also said it would be best to at least have a set of guages to hook up for the readings of the system. Personally, since I'm not familiar with A/C service (never had a car where one worked ) I'm going to look for one of those A/C services ads and then watch them like a hawk while they do their magic on my Benz.

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1991 300SE (my ride, 279,000 miles, looks almost new
1954 Cadillac (21 yo son's car, he bought when age 15)
1972 SeaBird 19 ft runabout (old but solid, slant six, Volvo sterndrive perfect condition, undergoing complete overhaul and refit)
1998 Toyota Rav4 (my sons daily driver when he is in the Continental US, PROUDLY serving in US Navy)