ilm

I have an 04 e320. I noticed that when I am using my A/C and I hit the A/C off button I still get cold air from my vents (not cool, but cold air). I called my dealer and they told me to bring it in for service. When I returned to pick up my car, my service advisor told me that there was nothing wrong with my car, and it was operating as designed. I then asked why do I have an off button for the A/C system. He responded with it will mix with air from the outside, but the compressor will never shut off. We went round and round and I finally just left. I did not believe him.

Does anyone else has experience with this? Is the A/C compressor always supposed to run? If so, what does the A/C off button do?

Thanks any thoughts you can provide.

adam3

i've noticed that even with the A/c off the temp control still works OK

MB-JIM

The AC Off Button shuts off the AC Compressor. This is the mode that is normally used in the winter when you don't need cooling.
If your windows start to fog insided with AC Off, put the AC back on since it will de-humidify the air. You can simply leave the AC On all the time but you should save some fuel if the AC is Off.

DaveFr

The A/C compressor should shut off when you push the A/C Off button. On my car I can hear the difference between the A/C compressor being on or off while the car is idling. If the service advisor told you they determined your compressor was always on and was operating normally, then they don't know what they are talking about and you should escalate the issue to the shop foreman or the service manager.

Does the cold air continue to flow long after you pressed the A/C Off button? On my car I've noticed that it takes a few minutes for the cold air to stop flowing after pressing the A/C Off button. It just takes awhile for the system, which has had cold air flowing through it, to warm up to the outside air temperature.

ilm

Yes, the air comes out colder then outside air even if the A/C off button is red. I drove all the way home yesterday from the dealership in 90+ degree weather and the A/C was off. Everything I was told by the service advisor just didn't make sense. I will be writing a letter to the owner of the dealership.

jim256

The A/C does have a humidity sensor and will activate the compressor if it's too humid out, and mine always activates it at morning and other start-ups even with the A/C off button set prior to starting. Other times, however, it shuts off the compressor immediately. I will typically turn it off a mile from home to allow some plain air through the system to hopefully prevent mildew odors. It always turns off and air gradually warms.

mahwahdave

I posted the same question a few months ago...I spoke to a tech who explained how the AC/OFF button works. The switch actually puts the system into "SLEEP" mode. The system will continue running the compressor and will gradually shut down....I notice the cold air for about 10 minutes before it shuts down each time I start the car with the AC/OFF. This feature is suppose to be more comfortable for the driver. I think it's a stupid feature. Most driver's leave the AC on and will never notice this. I find it annoying when driving with the sunroof and windows open on a nice warm day.

ilm

mahwahdave: Thanks for the response. So far that is the best answer I have received. I will still be writting to the dealership based on the fact that the service advisor was rude. He was talking to me like I was stupid.

Rudegar

I agree with you that mahwahdave's answer makes sense. I have found the same thing -- turn off A/C and after 10 minutes or so, the air warms up.

Spartan

Wait a minute guys, if I remember correctly, the compressor ALWAYS keeps spinning in order to circulate it's oil. As far as I remember, it has a bypass valve that will not let the compressor build up pressure.

In my 95 E, I noticed that when I shut it down, the air was still cool for a short while. I attributed that to the AC system inertia. In other words, shutting it off does not mean that the system stops dead, it means that the system loses it's latent capacity.

alewifebp

I was wondering about the same thing for a while too. I used to think the function was broken. Kind of annoying, as I also like to, at least on the cooler days, to turn off the compressor before I get home so that the coils can dry out and not create that mildew smell the next time you start up.

So, I would have to turn it off like 15 minutes or so before I got to my destination, which is a little too long for my Nordic blood to be without A/C when it is hot outside.

Romsdahl

Ditto - I have an '05 CDI, same observation, same question to dealership and same answer. Compressor actually does disengage.

rbordel

You could try using the "rest" feature (if your car has it -- it's supposed to be discontinued soon) to circulate air after engine shutdown to dry the evaporator coils. The compressor will certainly be off, since the engine is not running, and the fan is supposed to shut off automatically after 30 minutes. The rest feature is also supposed to shut down if the battery gets too low. I'm testing it now to see how effective it is combating the mildew smell.

andyKen

I have an E320 CDI with Lux Climaate Control and find that I DO sometimes get a 'mildew odor' when I start the car, for a minute or maybe two.

Is this normal? Has anyone else ever noticed it? Is Jim's suggestion the best way to solve it?

Thanks for any help.
AndyK

alewifebp

The mildew smell is normal, since, well, it probably is mildew that was left as the colling coils warm up and the water doesn't drip out. And which explains why the way that it is designed is not optimal.

shorthair

Unfortunately it is normal for the car, but should be unacceptable for anyone as that mildew smell is really bacteria growing in your evaporator and you are inhaling whether or not you can smell it. (The bacteria made me nauseous whilst in the car)

The dealer will probably tell you they will put in some stuff (Ozium) to fix it. That will make it smell like musty Ozium for a few weeks and then it will return. The only real "temporary" fix is for them to flush the evaporator housing twice with DWD2 Cleaner, MB part number 200-009-50-83, then to replace the dust and charcoal filters.

I say "temporary" fix as the A/C design is faulty for letting the moisture collect in the first place (older MB cars and many other makes do not have this problem) and the problem will return as the A/C system is never off, and as reported elsewhere, the EC button does not turn the A/C compressor immediately off but lets it gradually power down to abut 10% of maximum after about 10 minutes, which makes it very difficult to run it for a few minutes before stopping to try and dry it out. If you press the EC button then turn the fan completely off then on again the A/C compressor will immediately go to low power mode.

MB really needs to fix the design to properly fix the problem.

glojo

Hi Shortair,
Your very informative response corroborates what I, and a few others have repeatedly said, "We are developing this excellent vehicle on behalf of Daimler Chrysler"

What on earth has happened to the research and development department? Does saving money really mean this much lack of development?

Have you considered writing direct to Mercedes-Benz outlining your observations (You certainly appear to know your subject)

Will this mildew cause premature corrosion in the air conditioning unit?

Thanks again,

John
Overcast Torquay

RJC

The smell is due to the condensation drain pan not being angled enough to allow for proper draining. This was a similar problem on 2003 CLK 500's. There was a TSB for this problem.