With the help of those who have responded to my Klima question, I've now found the cause of my problem. Now I need to impose upon you all for one last question. I'm not sure what the item is called, but I am speaking of the piece that has the sight glass on top of it to view the freon. My car is an 88 300SE.

This item has 2 sensors attached to it. The one on top activates the aux fan when jumped. The bottom one is part number 124 820 59 10 and FastLane says it's the "A/C Pressure Switch". When I unplug the 2 wires running to it and jump them with a piece of wire my climate control system works PERFECTLY!! The a/c compressor engages and disengages depending upon what button is pressed and what temp is selected. I checked this and removed the jumper wire so as not to mess anything up. I figure if MB has this switch in for some safety reason I didn't want the compressor engaged if MB wanted it DISengaged.

So, my last question is, what does the A/C Pressure Switch monitor before allowing the compressor to engage? Is it the pressure of the refrigerant (134a in my case as it has been converted) as I'm guessing? I dropped the car off at my local shop yesterday but they didn't have time to check the a/c system but will Monday. My guess is I'm either low on refrigerant pressure or the switch itself is bad.

I'd love nothing more than to be able to let them know what the problem is and save myself some money in having them charge me for hours of diagnostic work.

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Thanks,
Ron Brooks