I've noticed a couple of posts about air conditioning on older cars, and here are a couple of observations from my experience:

Convert to 134. It's way cheaper, and you'll be doing the right thing with the environment (freon eats up ozone in the atmosphere, allowing more uv through than what most living species are designed/evolved for).

On the Bosch unit, make sure you drain the oil and replace before filling with 134 coolant. the ac shop will also replace some nipples to "standardize" your system.

Another important thing is to replace the cannister that catches moisture (forgot it's name), about 100 dollars at NAPA.

So far (almost 1 year) the conversion has worked perfectly. Plenty of cold air, no leaks or damaged compressor. It gets heavy use here in Hawaii.

AC guy says the piston type systems (Bosch) work very well with 134, something about conmpression ratios...

Make sure your fan relay works. This is the auxiliary fan right behind the grill that cools the ac radiator.

total cost of conversion and fillup with 134 was less than a fillup with freon (r12).

aloha,
andres yver

'81 528i
'62 VW pritschenwagen (single cab pickup) - horse manure hauler for the veggie garden...