well, you are going to have to get some numbers first. My guess is it's low, and the condenser is dirty. are you SURE the aux fan is running all the time? those symptoms really point to a bad or sporadic aux fan. remove the aux fan, get the condenser clean, remove the bugs and dirt/grass etc from it, and spray some degreaser on it and rinse it off well. test the temp sensor on the R/Drier clean the connections really well and put some di-electric grease on them. see if it helps. but most of all, get some guages and find out what the pressures are.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!