A/C cooling in my 2005 R171 SLK was intermittent for a few months (thankfully, not too much in the summer). This past winter, it became increasingly problematic, causing the windscreens and windows to fog up frequently (depending on humidity levels, the A/C compressor is supposed to kick-in in order to dehumidify incoming air before it is heated and blown into the cabin). Using an iCarsoft scanner, I saw this error code for the SAM: 9000 component or the signal line to the component a9 (ac compressor) has open circuit or short to ground
With the defogger on, I could also see that the A/C compressor would actually turn on reliably (to dehumidify incoming air before it got heated up and blown over the windscreen) but would fail to turn on during normal use of the climate control. Thus, while the defogger works effectively, humid air would be blown into the car during normal use of the climate control, with frequent use of the defogger making the cabin uncomfortably hot and noisy.
I fixed this issue by taking out the front SAM (fairly simple, but a bit time consuming), and prying it open. I ultimately had to cut off part of the plastic cover with a hot soldering iron at two edges and lifting it up and out. Apart from one overheated capacitor, everything else looked good. I replaced that capacitor (bought for 48 cts), and that tiny fix appears to have successfully fixed the A/C problems.
The common recommendation for any SAM issue is to replace it. Dealer had quoted 650 USD for a new module, and 480 USD for the labour to swap it out and code it (~1,200 - 1,300 total quote is common across many dealers). Unfortunately, local indie mechanics with DAS equipment indicate that modern SAM, including the R171 one, can only be coded by a dealer if purchased new. Used SAMs may not need coding, but aren't reliably tested.
If any of you face SAM issues, I would recommend trying to fix it as I did: Take it to your friendly electronics guru/tech to check out, or simply attempt to replace any burnt out components yourself (in many electronics, that's usually just a capacitor or two). I spent 0.48 USD (and an hour or two of my time), vs ~1,200 USD.
NB: apologies for the fuzzy pic. Too lazy to take out the SAM for clearer pics.
iCarSoft scanner, highly recommended, since it can scan specific equipment in the car, which can't be done with a standard OBDII scanner: https://www.amazon.com/iCarsoft-Genu...rsoft+mercedes