I went to anglo canadian for a quote and they were charging quite a lot for my W203 C class, Ended up selling the car and letting the new owner take care of it. It was something like $3000 to get it fixed so I was like Fuck it,
If your driving a 1990 740 the A/C replaced might be more expensive than the car

Not to sound mean or nething. depends what it is of course, And it's not a benz so it'll prolly be a bit cheaper XD
So glad the AC on my Z31 is freezing, except you can't really adjust it its freezing or nothing... lol