So, I am now on A/C compressor #4. Trouble began as a slight noise in my 2008 S450 (59,000Km). Compressor was on its way out in my opinion. So, I let is roll for a bit and yes got progressively worse. A call to Rock Auto for a replacement Compressor, Expansion valve and Receiver / Dryer.
Swap out parts, do a flush and I am off, for about 8 months. Same issues. Complain to Rock Auto - defective compressor. No problem sir, order a replacement and we will credit on return of the defective unit. Off I go, flush,, replace compressor valve $ dryer. Rock auto receives no unit, examine by GPD - full of dirt and still has flush in it? What?? not my first rodeo but my bad, no worry sir we will warranty regardless. Great service..
No 2 months go by, noise again, wtf? Do the whole process again, this time the replacement compressor wont engage at all. Grrr, off to Mercedes to see if the system has "forgotten" the A/C. Nope, all good, STAR says current going to A/C. Compressor needs to be replaced. Order again and this time tell Rock Auto - compressor DOA. Replacement sent installed and credit received for defective unit.

New units works, cold air and a big smile for 4 weeks. Then its back again. I start kicking myself for what must be my poor skills at A/C work, but after second guessing for a few days - NO, I do know what I am doing, Something else is up. I dig into the interweb and find an obscure reference to bad a/c lines. I call up my local dealer who say they have never hear of such an issue but will look around for me. Low and behold, yes TSB, change the upper and lower return lines $550 for the line alone.

Okay, this time lines, compressor, valve. dryer, condenser but not evaporator. Flushed what I can and off I go... for 3 days.

So now, what besides change everything again?
Anyone have any experience installing inline filters and service valves?

 

You keep buying reman compressors from same place and they keep failing. I would try another compressor from another place.

Also, does the system hold charge? You put in right amount and type of refrigerant? Just random thoughts.

 

Yup, were it so simple.

I did return to the same supplier as I purchased from as I first thought it was a warranty issue. When I ran into subsequent problems I went with a different vendor - Nissens.

And yes, the system is tight and holding pressure.

As a follow up, I tore my system apart and flushed the crap out of it figuratively and literally. Though I changed the compressor, condenser, low pressure - upper and lower hoses and flushed the evaporator I still had a huge amount of crud come out of the system on this second go round.

My conclusion, I did not get the evaporator clear on the first go.

So, and all the A/C Tech will cringe at this. I flushed with mineral spirits until it flowed clear, dumped the oil out of the compressor and receiver dryer and "washed" it out as best I could, then followed up with a flush with an Ester oil based solvent (FJC product). I purged with compresses air and vacuumed the system for an hour and recharged.

My thought train is that everything is screwed anyhow and I have nothing to lose. My next steps may be, if this does indeed hold up, run the system for a few weeks and then pull the compressor and receiver dryer and do an Oil and Filter change.

Oh, and to give the purists even a bit more pain when I re-oiled I mixed PAG 46 and PAG 100 to give a higher viscosity.

To follow up and preamble further anxiety from Members, this forum is not, in my belief, dedicated to how to do it as per the text book, I have a WIS. It is how to keep your car rolling and keep $1,000+ in your bank account. The theme of necessary and sufficient should be our motto. Not, change all the part or take it to a Dealer.

When I was into this for the (I think 3rd time) my lovely lady said maybe I should take it into the dealer. I thought (inside voice no way, they charged me $250 just to tell me the compressor would not engage) well, I might as well get a quote, I told her:
To replace A/C Compressor (parts only $1,200 , lines $565 for the pair as per TSB, evaporator $865, expansion valve $125, condenser $985, receiver dryer $185, R134 $225, PAG oil $55 and labour ~ $4,200. They were guessing here because they have not needed to replace an evaporator on an S and believe that they can flush vs replace) so about $5,000 parts and $1,500 -$3,00 labour.

So, I can still play lots and keep my bank account intact and after the initial "grr" and not fixing on the first go, the gauntlet has been thrown and I am ready for the ongoing challenge.