The topmost switch on your AC Receiver/Drier is the pressure switch...if you jump that and your compressor clutch engages....it is most probably a lack of refrigerant......disconnect your jumper, and leave one of the wires disconnected....until you get your system charged.....
I have my AC Compressor clutch disabled in this manner......so that it will not attempt to engage when the defroster is in use.....otherwise I use the "economy" mode on my Klima........ 
SB
also of note: I have shopped around the area for a good automotive AC shop (I sold all of my AC recovery equipment and tools/instruments some time back).....my local MB dealership will replace my compressor with one that I supply, along with the drier and expansion valve.....do the R1324A conversion....flush and purge the system for $60.00/hr or about $300-$350......if I supply all parts.....they will not be responsible for any labor warranty.......if they supply the parts and warranty the whole deal it will be around $1800.00.....
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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG
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