Originally Posted by L1Wolf

Maybe, but some things should default to optimized settings. Just because the AC is enabled doesn't mean the air compressor is on and trying to extract heat from the inside air. The computer manages the system and turns it on when conditions require it. Turning it off will prevent the computer from using that option. My opinion is to let the computer do its thing and don't hinder it. I wonder why you can even turn it off. Maybe there is a legit reason to, but the temperature outside may not be one of them. I don't really know though which is why I let the computer figure it out and just enjoy the car. Another climate control setting that resets is the recirculation setting. It will even reset after so much time while driving, but also reset after a shutting the car off. The reason why is that the car is pretty much air tight and turning on recirculation will eventually deplete the oxygen in the car. It takes a while but it can actually make you sleepy which is bad. I mention it as an example of decisions that are made in the operations of the systems in the car to reduce issues. Maybe, there is a good reason to have the AC on all the time and therefore default to on with every startup.

Originally Posted by gleam

In the 450 the compressor is all electric (no belt off the engine and so clutchless), variable displacement, and runs off the 48V system rather than the 12V system. It's a variant of the Brose G43852 that has been used in the S class since 2021. In the 350, though, it's a Denso 6SAS14C, belt driven with a clutch, but still variable displacement.

Variable displacement compressors are much more efficient because they can scale up/down their cooling output to meet the needs of the climate control system. If it's not needed it will be at minimum displacement and have basically no effect and draw an insignificant amount of power, or on the E350 it will disengage the clutch and draw no power at all.

I didn't realize until researching this that the E450 gets a slicker compressor than the E350, and to my mind it's another reason to get the E450 -- the AC should keep blowing cold even if the engine stops as part of the auto stop/start.

Originally Posted by W205C43PFL

I am always curious, are A/C compressors in cars similar to home units controlled by the thermostat, which they have cooling off periods, to prevent short cycling and protect the compressor?

Originally Posted by gleam

good question! With the variable displacement compressor the idea is that as you near the set temperature it dials down the displacement to the exact level needed to maintain the temp, rather than turning it off and on repeatedly. So instead of running at 100% capacity for a minute and then off for a minute, it will run at 50% capacity the entire time. They’re also usually much more power efficient when running below max displacement.

If you get a new air conditioner at home and it features multiple speeds or variable speeds for the outdoor unit it’s the same idea. More efficiency when running longer at low power.

Originally Posted by gleam

good question! With the variable displacement compressor the idea is that as you near the set temperature it dials down the displacement to the exact level needed to maintain the temp, rather than turning it off and on repeatedly. So instead of running at 100% capacity for a minute and then off for a minute, it will run at 50% capacity the entire time. They’re also usually much more power efficient when running below max displacement.

If you get a new air conditioner at home and it features multiple speeds or variable speeds for the outdoor unit it’s the same idea. More efficiency when running longer at low power.

Originally Posted by JTK44

To the best of my knowledge, AC units on cars are not variable: they are either on or off.

see: https://www.google.com/search?q=are+...t=gws-wiz-serp

Originally Posted by W205C43PFL

Could it be that the one in the W214 is?

Originally Posted by JTK44

It it runs off the battery, then I think it would be constant speed: either on or off

Originally Posted by JTK44

To the best of my knowledge, AC units on cars are not variable: they are either on or off - but they can run at different speeds depending the on the RPM of the engine.

see: https://www.google.com/search?q=are+ac+units+on+a+car+fixed+or+variable+s peed&sca_esv=c9ba1905e1b36b97&rlz=1C1SQJL_enUS888U S888&sxsrf=AHTn8zqw4lK1EJYup5hMEspgdilPUWRUIA%3A17 39238363607&ei=26uqZ8rmJNGA5OMPo9-ciAM&oq=are+ac+units+on+a+car+fixed&gs_lp=Egxnd3Mt d2l6LXNlcnAiG2FyZSBhYyB1bml0cyBvbiBhIGNhciBmaXhlZC oCCAAyBRAhGKABMgUQIRigATIFECEYoAEyBRAhGKABMgUQIRig AUjrTVC7DViRO3ACeAGQAQCYAccBoAHkD6oBBDExLji4AQHIAQ D4AQGYAhSgAvARwgIKEAAYsAMY1gQYR8ICBBAjGCfCAggQABiA BBiiBMICBRAAGO8FwgIIEAAYogQYiQXCAgUQIRirAsICBRAhGJ 8FmAMAiAYBkAYIkgcIMTIuNi4xLjGgB4p4&sclient=gws-wiz-serp

Originally Posted by gleam

Additionally, the compressor in the W214 E450 doesn’t run off the engine at all, it’s beltless and is powered by the 48V battery.

Originally Posted by JTK44

see post #32

Originally Posted by jumpman726

Sorry guys, it looks like I made my original post prematurely. I drove my E today a couple of times and I opened up the climate menu each time to see if the AC was activated and it wasn't, which means the car remembered my last setting when I turned it off a couple of days ago. The climate control was still set on AUTO at 70 degrees, but the AC button was not enabled at startup, which is what I wanted.

By the way, I love driving this car.

Originally Posted by kjb55

I have limited time in my W214 / E 53, but in all other MBs I've owned and 100% using Auto climate I am in the group of being aware whether or not the A/C compressor is engaged. My biggest gripe is turning off the car and the condensation that creates the mold issue in the vents. My 2003 Volvo had a sensor that would circulate the fan for up to 20 minutes to dry the system.

These are my observations...

• Pressing Auto activates the A/C function. With DAS / Xentry hooked up and viewing the compressor clutch readings - it is engaged at some percentage regardless of ambient temperature.
• To get Auto climate without A/C - ignition 2, press auto, press A/C to deactivate. Press off to turn off the entire system - press off again (rather than Auto) and it will turn back on to full auto remembering that the A/C function was off.
• As for the E53 - you can have a climate shortcut as part of the bottom of the screen - recirculate, A/C and something else. I chose A/C to accomplish the above. After driving for sometime - <30min - the A/C activated by itself. The red line under the A/C went red. That hasn't happened on my previous models.
• So - my efforts are thwarted by the new system architecture. Guessing there is a comfort sensor (humidity?) that reads air quality and adapts.

Change is good.

Originally Posted by kjb55

I have limited time in my W214 / E 53, but in all other MBs I've owned and 100% using Auto climate I am in the group of being aware whether or not the A/C compressor is engaged. My biggest gripe is turning off the car and the condensation that creates the mold issue in the vents. My 2003 Volvo had a sensor that would circulate the fan for up to 20 minutes to dry the system.

These are my observations...

• Pressing Auto activates the A/C function. With DAS / Xentry hooked up and viewing the compressor clutch readings - it is engaged at some percentage regardless of ambient temperature.
• To get Auto climate without A/C - ignition 2, press auto, press A/C to deactivate. Press off to turn off the entire system - press off again (rather than Auto) and it will turn back on to full auto remembering that the A/C function was off.
• As for the E53 - you can have a climate shortcut as part of the bottom of the screen - recirculate, A/C and something else. I chose A/C to accomplish the above. After driving for sometime - <30min - the A/C activated by itself. The red line under the A/C went red. That hasn't happened on my previous models.
• So - my efforts are thwarted by the new system architecture. Guessing there is a comfort sensor (humidity?) that reads air quality and adapts.

Change is good.