The compressor on my '85 wagon was locked up when I bought the car a couple years ago, and now that the temperature's climbin' I'm about ready to have it work.

I've never done ANY A/C work before, and am not really sure where to start.

The compressor unit says "Delphi 4354" on it, and I'm assuming it's an "R4" compressor because it looks similar to the photo HERE.
On the Delphi site, that part number seems to "cross" to a "CS0012," which only shows applications for Chevy + GMC, and runs like $300 online.

What the heck is an R4 compressor, compared to R-12 and R134?
Is there any reason to switch systems, and is there a certain compressor, manufacturer, or source you'd recommend?

I'm assuming the first step is to get a leak dye test, and hope and pray that there's a leak in a hose or fitting, and not at the evaporator or something?
What should I expect to pay for the leak test, and can one shop do it just as well as another, or would you stick to a Mercedes specialist?

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250