1-Not sure where the low pressure switch is on ML; on my 300E it is located right on the receiver/dryer as is the high pressure switch.

2-Price for the compressor I recently purchased for 300E was $355. with the clutch being $104. Add to that was a core charge of $93 which was refunded when I returned the parts I removed. The compressor I purchased was a Denso remanufacted compressor. What was important to me was that it was remanufacted by Denso in Japan, which it was. Lots of companies remanufacter Denso compressors but I figured the best ones came from the orginal manufactorer, hope I'm right. Frankly what I put on looked brand new. The compressor does not have the clutch installed but it's not that hard to install.

3- I got my parts from Phillips a mercedes dealer in Virginia Beach. I felt it was best to buy an item like this from the dealer and frankly I think their price on this item was less than I could have gotten it elsewhere.

I do recommeded putting in a new receiver/dryer at the least and a new expansion valve too.