Having read numerous horror stories about problems with AC in the w140 (I have a 92 500sel), I am wondering if there is any preventative maintenance that can be done to avoid such problems.

My system seems to run fine now (gives 40F out of the center vents on 100F days at 55mph). The only "problem" I have seen is that twice over the summer it cycled off (after a full throttle blast in hot weather), and then failed to cycle on again. It fixed itself after turning the car off and on again, and like I said only occured twice (in about 10k miles worth of driving...)

I asked a friend here who is an accomplished AC tech, and he said that if it is working, don't mess with it. Any intrusion into what appears to be a properly sealed system will do more harm than good. Sounds reasonable.

So, the question is: Is there anything that I can do to insure longest life for the AC components?

TIA

-David

I've always heard its best to use the automatic settings (though I am unfamiliar with 140's). Let the system work it self and use AC in the winter. I think the defrost setting uses AC at any temp. Avoid setting the system to extremes (max fan/min fan). Just let it make its own adjustments, and keep limber.

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14

Like A264172 said, it is good to 'exercise' the system once in a while during the cold weather months to keep parts properly lubed and sealed. I think modern MBs are designed to kick in the a/c once in a while, such as during startup. Using defrost will definitely activate the a/c. Beyond that, there is no other maintenance that can be done to your system. You pretty much leave it alone and only service it when anything goes wrong.

Dave, your friend is correct about leaving the system alone and avoiding any mechanical intrusion.

The reason your system cycled off during full throttle condition is because of belt slippage. The system senses when the belt slips on the a/c compressor so it can shut down the compressor in cases where the compressor starts siezing in order to prevent loss of the serpentine belt. Losing the belt would leave your car dead on the side of the road. The a/c system will reset next time you start the car. You should take this clue and consider you may need a new belt, a new tensioner, or both.

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95 E320 Cabriolet, 159K

Thanks, this is definitely some good info.

As for the belt slipping, I do get a "chirp" during a hi rpm shift, which would also point to belt slipping.

However, both the belt and the tensioner were replaced less than 10k miles ago (when I first bought the car), so maybe it just needs to be tightened?

-David

There's no tightening that can be done on a belt design that uses a tensioner. It sounds like the driving you do with the a/c on is the design limit of the belt to where it slips a bit during shifts.

The fact that it only happened twice during your Arizona summer tells me your system is designed properly, being on that 'fine edge' without being overly tight.

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95 E320 Cabriolet, 159K