Stuttgarten

I ‘m posting my experience with climate control REST function.The climate control unit seen in first picture came from an ’07 W211. As could be seen there’s no REST button, so I assumed that capability was not present. But a few nights ago, I was sitting in the car, engine was off, outside tempwas around 75’F, and 10 minutes later I heard a faint sound of something coming on. I saw REST function came on, as pictured in dark picture. I placed my hands near the air vents and felt very gentle warm air flow which lasted for about 20 min, after which it shut off by itself.


I was pleasantly surprised, so I thought I’d document this to shed some light on that function!

kajtek1

Nice find Al.
I did notice the REST on my original LCD display (visible at angle against the light), but with no button assumed it is disabled.
I am still confused how you did get it coming on just by sitting in 75F.
For me REST function is useless, but I liked the sensor reading it activate, so I replaced my climatronic with 4-zone one, that has REST button and is allowing me check the car system without leaving driver seat.

Stuttgarten

I like that diagnostic feature on the 4-zone system. I'm curious if other drivers have had my experience in that REST function comes on without driver direct input. I'm also wondering if it would come on with no one sitting inside car!

kajtek1

Did you have key in ignition?
What is your thermostat setting?

Stuttgarten

Key was not in ignition. Thermostat setting was on blue mark, coldest setting.

kajtek1

I READ THE MANUAL and there is no word about such option.
Actually manual says that the REST is Canadian-only option, when our 4-zone car is US model and does have REST button.
Than ebay is flooded with 4-zone climatronics that come from US dismantlers.

benzslo

Did you ever figure out any more info. Little disappointed when I realized my 08 doesn't have rest. I'd like to have it for sure. I work at dealer so maybe I'll see if I can change some coding to Canada version.
When it comes in for you were doors locked or unlocked?

kajtek1

You can buy 4-zone climatronic on ebay very cheap and it is direct replacement on lifted W211 models.
I did it on another car not for REST, but for sensor reading option.
The car health scan would show the climatronic not paired to the car, but it worked just fine regardless.
How it happen on Stuttgarten's car reminds mystery?

Stuttgarten

I don't know what was getting that unit to get into the REST mode. It was done automatically and only after I'd park the car. I'd have car parked in garage and a little later as I'm passing by doing stuff, I'd hear a faint hum and when checking the A/C control unit screen, I'd see REST being on. As I said earlier this unit came from an '07 W211 and it was a direct fit. Certainly, as Kajtek said, the 4-zone climatronic is a more "intelligent" unit and would give a lot more useful info.

kajtek1

We also have some reports about REST coming on W212 cars, who never had REST button.
Make me wonder about other possibility.
When the REST buttons were introduced on W210 models, its sibling W163 (ML class) was using electric pump to eliminate engine "hot spot" after shut down since in heavier SUV the same engines would work harder.
So could it be on newer cars, that when you shut down hot engine, the computer will run REST for the same purpose? That would explain how it happens without driver action?

benzslo

The rest feature you guys are reporting of that comes on automatically in warm weather is likely the after blow function, for sure on the w204 is probably the car that started it, w212 had the issues also. Maybe they were doing it on w211 and I just don't recall, over 10 years ago and they never really had the problem to start. They started doing that in the late 2000's because they had alot of concerns with mold and mildew smell from the vents. The after blow feature is to blow all the moist and condensed air out of the hvac box. I'd be very surprised if it does that on its own in cold weather. Today I tried changing a coding to Canada and changing model year of the unit hoping it might turn the max cool button into rest function, but no luck. At least my 08 ml has it.

kajtek1

Seems engine hot spot cooling and after blow is the same function.
Make sense either way.