So it's winter time and I've never turned the A/C on during the winter. I have the climate set to AUTO and I noticed that my new E turns the A/C on each time I start the car even if I've previously turned the A/C off.

Someone please tell me there's a way to change a setting so the A/C remembers my last choice (whether ON or OFF). I read the manual and it seems like there's no way to do this with the AUTO setting activated.

If it were summer I would be fine with the A/C turning ON each time, but having to constantly turn it off in the winter would be annoying.

I feel there's no need for A/C in the winter because it uses more fuel and puts more strain on the engine making it slower.

 

Just because the A/C light is on it doesn't mean that the compressor is actually engaged and running. Think of it as disable/enabled becuse the compressor only runs when it is necessary to provide cooling.

 

With A/C on, mine blows warm air in the winter and cool air in the summer, usually set at 70 all year.

 

Sounds about right as it is recommended to keep it on all season, in the winter it removes humidity.

 

https://mbworld.org/forums/eqs/90115...ml#post9049645

 

Not true at least on my car: 2019 E450. I always keep in Auto, with AC off. When I go to start the car, my AC is still off. I agree with you, that keeping the AC decreases fuel milage: i.e., you burn more fuel with the AC on than off.

Hope this helps.

 

Yes it is mixing warm air with cooled air: when you run the AC you burn more fuel. When the AC comes on and off, you can hear it - at least I can.

Remember even if it is zero outside, if you put the car in defrost mode, the AC comes on to clear the windshield. In Auto, with the AC on the same: it is on.

 

I just read the above thread: Leaving the AC on in the winter decreased the range of the EV by 25/35 miles: It is on and draining the battery. Same thing in an ICE. It is on and will burn more fuel.

The only time in the winter I leave the AC on is when the windows get fogged.

In Vermont when it is zero, if I hit the defrost and have the AC on, it takes much longer for the heat to defrost the window. With the AC off, I get hot air much quicker.

Turn the AC off in the winter: it will save you money.

 

Fair enough : )

 

It’s my understanding that the a/c compressor on the 450 is electrical - not belt driven so it shouldn’t cause any engine strain or use much more fuel other than what it would take for the ISG to replace the energy to the battery.

 

I think many are over thinking this. I leave it on auto and the A/C enabled which means the computer manages when the compressor is on based on the real-time conditions. My belief is that any fuel efficiency gained by turning off the A/C manually is negligible at best and may not even amount to any improvement. Not enough to worry about IMO. It's an automatic climate control system. It's likely best to let it determine how to regulate the interior climate and just set the temp.

 

Uhm: never thought of that and you may be correct

 

There's no point in running the climate control system when the windows are down. Mine are down most of the year except when it is raining.

 

Windows down might make sense up to 20/25 mph. I tend to drive a bit faster, often 75 mph +. At that speed, with the windows down, the inside of my car would be like standing out in a hurricane!

 

Or open the sunroof in ventilation position but still not ideal. The good thing is as speed increase, the vehicle automatically closes up the sunroof automatically and open up wider when the speed is dropped, this is especially true for ventilation mode.

 

True I forgot about that as well.

 

I want to add something, especially with all the fires, I recommend using the climate control and let the HEPA filter if EQS and equipped or the activated charcoal cabin air filter in the cabin to do the filtering, instead of, say your lungs.

 

Who said anything about the windows being down? We are talking about leaving the A/C on in the winter.

 

My car has never been on a highway or over 50 mph. It is a city car.

 

I don't agree with having the AC on during the winter when I'm trying to heat my car. The warm air already lowers the relative humidity in the car. Does anyone run the heat and AC at the same time in your home? I didn't think so.

On my old E class I just set it on Auto with the AC off and I never had an issue with the windows fogging up. Also, it remembered my last setting at each startup, which was the point of my original post.

The car should remember the driver's last setting instead of defaulting to turning the AC on at every startup.

 

The theory is that yes while you were heating the air, it does get warmer but warm air holds more water, even though the humidity is less. That is the relative nature of humidity. That warm, humid air is what now condenses on the cold window and is usually why the fog appears after the heat is turned on..

and yes, there are some interior home units that do exactly this for humidity control and it is called reheat. Effectively you are running a heater with air conditioning or vice versa and it’s about humidity control.

but as all others see, the heating time does take longer during defrost. My preference is AC off until the car heats up. Or I get the car very hot and crack a window for a second to release the moisture out of that air..

 

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.

 

If your statement is accurate about the AC compressor not being on all the time if AC is enabled then I would be fine with that.

Can anyone confirm that?

I thought if the AC button is on then the compressor is constantly running.

 

The compressor cycles to maintain the set temperature.

 

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.