It's that time of year and I've just finished performance testing the Freon 12 A/C of my 1986 240 wagon this evening. Exterior conditions: 78F and 40% humidity, the A/C set on recirculate, the fan on high and the A/C temp turned all the way down, the air from the central dash vents was
44F. Cold enough to be uncomfortable blowing on bare skin. However, when I looked through the sight glass on the receiver/dryer I see "smoke", not clear glass, not bubbles, not oil. I've been told that this is the sign that the dessicant in the dryer is failing and it is now releasing the water it's absorbed over the last 19 years back into the A/C system. I really, really need to get one more season from this A/C and I want to know if there can be serious harm done by continuing to use the A/C with this condition. If the A/C should simply stop working I'll bite the bullet and pay to convert to 134a, but a damaged compressor, evaporator or condensor will be serious $$$.

Just an opinion, but if it's still blowing cold after 19 years, I would keep running it.
if for some odd reason the compressor folds in a few more years, a new one only cost about $225, until then, enjoy your R12 while it lasts.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale