04 CLK 209 (facelift) 270CDI Aircon settings
 

Hello, MBworld! I have read that it is better to leave the AC on always and never use the AC Off button. The logic is that keeping it ON lubricates the system and keeps it in top condition. I just wonder how do you approach the AC in general. I think I just leave the knob at around 21 and never bother.
Share your opinions on what is optimal and why, please.
Regards, DS.

It's in numerous articles (via Google search) that running a car's A/C for about 10 minutes every couple of weeks or so is sufficient to keep everything lubricated and working well. I'm in So Cal, so I use the A/C a fair amount year round (including in the winter for defrosting purposes and on warm days), so this isn't really an issue for me.

To add some anecdotal information, my wife had a Jaguar X-Type about 10 years ago and ran the A/C all the time. Sure enough, it quit cooling on hot days when it was about 4 or 5 years old (maybe at 75K miles?). No idea what the problem was; we sold it to Car Max and it became their problem.

Conversely, I've always used the A/C only when I want A/C and otherwise leave it off. My A/C has never broken in any of my cars (except for some beater I had in high school). Maybe coincidence, maybe not.

So I guess my answer is highly subjective (and may not even be accurate at all), but it would seem logical to me to just use A/C when you need it in order to preserve the components as much as possible. Otherwise, just run it every other week or so to lubricate the system, etc. Also, if you're not using A/C, that's more power that your engine has.

I always leave the AC compressor on and the system in "auto" mode. i then adjust the temperature to my liking (usually right around 70C/21C). I find MBZ's ACC does a good job of regulating the temperature and airflow in most conditions. I don't find that the AC compressor puts and significant drag on the engine that adversely affects performance so I see not need to ever shut it off. Also, it uses an internal swash plate as opposed to a clutch, so when when cooling demands are low, it can actually cut back on the compressor's drag.