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Tried searching but haven't found a definitive answer. Have my 2024 e350 for 3 weeks now (love it), and I was always taught to turn off climate control before turning the car off, like with older cars. However, I hear that it no longer matters if you leave it on when you turn off the car, and the car doesn't require more energy to start with your climate control turned on.
What is the best thing to do? My guess is leave it on so when the car is remote started, the temperature will reach the ideal result.
In my estimation, leaving the AIr Conditioning compressor on during shutdown is not much of a terrible problem.
But consider the starting process. AC compressors usually have a 30 amp circuit breaker on them. 30 amps isn’t nothing, and is an unnecessary stress being put on the starter and battery. Also, compressors can consume 30 horsepower when running. 30 horsepower isn’t nothing when starting.
I make it a habit to turn off the AC before I switch off the engine. Also, I like for at least 2 minutes to elapse, with the circulation fan running to help clear out any condensation in the ductwork.
That way I don’t have to remember to turn the AC off prior to starting. On startup, I try to let at least 2 minutes to elapse before turning on the AC, allowing thorough engine lubrication before putting an additional load on it, and letting any hot air(hotter than ambient) pass through the ventilation system to ease the load going through the condenser.
In the long run, it doesn’t probably make a big difference, but it adds to my peace of mind that I am treating my car right, so it will never treat me wrong.
Last edited by MB2timer; Aug 18, 2024 at 02:06 AM.
Reason: 2 typos
I've thought about turning off the a/c before shutting off the engine, but worried about condensation in the ducts. While ON the system is blowing cold and dehumidified air through the ducts. As soon as you shut off the condenser, you've got warm, humid air running through nicely chilled ducts.
I've thought about turning off the a/c before shutting off the engine, but worried about condensation in the ducts. While ON the system is blowing cold and dehumidified air through the ducts. As soon as you shut off the condenser, you've got warm, humid air running through nicely chilled ducts.
If you have A/C > Rest then it is not something to worry about as long as you activate it before you leave the vehicle, just not sure what packages are required to have it.
Last edited by W205C43PFL; May 11, 2025 at 11:25 AM.
2024 and 2025 E450's and E350's A/C runs on the 48V battery, not the engine. So not a problem leaving the compressor on when shutting off engine. It was Mercedes genius to have the A/C run on 48v battery. I verified this with the Service Head just recently.
2024 and 2025 E450's and E350's A/C runs on the 48V battery, not the engine. So not a problem leaving the compressor on when shutting off engine. It was Mercedes genius to have the A/C run on 48v battery. I verified this with the Service Head just recently.
It was my understanding that the E350 compressor does not run off the battery but the E450 does. Is this not correct?
2024 and 2025 E450's and E350's A/C runs on the 48V battery, not the engine. So not a problem leaving the compressor on when shutting off engine. It was Mercedes genius to have the A/C run on 48v battery. I verified this with the Service Head just recently.
Originally Posted by silverse
Both E350 and E450 compressors run off the 48V Battery. My good friend has a 2025 E350 and his compressor runs off the Battery.
The E350 runs the air compressor off the gas engine. When using the start/stop and the engine stops, the compressor shuts off. The air is still blowing since the fan runs off the 12V battery, but the air turns noticeably warmer. In the E450 the air compressor runs off the 48V system and continues to run when start/stop shuts off the gas engine. I've had both the E350 and E450 and experienced this first hand.
This however has nothing to do with the OPs question of turning the AC off before shutting down the car. It's only relevant when the vehicle is on and the engine stops from the start/stop system. When you shut off the car, the AC turns off with it. You still have accessory power for the entertainment system but all AC functions are off on both models. When you open the door the entertainment system shuts down. When starting the car, the AC does not immediately come on. It takes a few seconds for everything to initialize. Leaving the AC on when shutting down the car does nothing to harm the car and there is no benefit to turn it off before hand. Running the car without the AC for long periods can cause mold, but that also has nothing to do with the OPs question.
I was informed by my good friend that his E350 A/C was off the 48V battery. I will have to inform him he is wrong, based on your response that you had the E350 and it worked off the engine. Thanks for the Clarification!.
2024 and 2025 E450's and E350's A/C runs on the 48V battery, not the engine. So not a problem leaving the compressor on when shutting off engine. It was Mercedes genius to have the A/C run on 48v battery. I verified this with the Service Head just recently.
The E350 runs the air compressor off the gas engine. When using the start/stop and the engine stops, the compressor shuts off. The air is still blowing since the fan runs off the 12V battery, but the air turns noticeably warmer. In the E450 the air compressor runs off the 48V system and continues to run when start/stop shuts off the gas engine. I've had both the E350 and E450 and experienced this first hand.
This however has nothing to do with the OPs question of turning the AC off before shutting down the car. It's only relevant when the vehicle is on and the engine stops from the start/stop system. When you shut off the car, the AC turns off with it. You still have accessory power for the entertainment system but all AC functions are off on both models. When you open the door the entertainment system shuts down. When starting the car, the AC does not immediately come on. It takes a few seconds for everything to initialize. Leaving the AC on when shutting down the car does nothing to harm the car and there is no benefit to turn it off before hand. Running the car without the AC for long periods can cause mold, but that also has nothing to do with the OPs question.
Do you by any chance know the reason for such differences? Are the two 48V mild hybrid systems different?
One thing that puzzles me is the pic on MB’s website of the 3.0 liter engine described as a lightweight beltless engine clearly showing a serpentine belt driving an alternator and a/c compressor.
One thing that puzzles me is the pic on MB’s website of the 3.0 liter engine described as a lightweight beltless engine clearly showing a serpentine belt driving an alternator and a/c compressor.
As I understand it, the key difference in AC functionality between the two are that the M254 drives the AC off a belt from the engine like most other engines. The M256 does not and has a fully electric AC driven by the 48v system. This allows the AC to remain active on the M256 when start/stop shuts the gas engine off while the M254 will turn off the compressor. In addition, the M254 is robbed of some of its 255hp to turn the compressor while the M256 does not use any of its 375hp for the compressor. It's a win/win for the M256 over the M254 with the more traditional setup.
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