anewbie

The AC sometimes gets a little too cold, so I turn off AC and turn on air recirculation. It stays on for a few minutes, usually less than 10, then, turns itself off. And all of a sudden, I've got a puff of warm air comes into the cabin. What's the deal with that? I've only read about automatic turning on of recirculation, but not turning off. Does anyone know why? Thanks!

Sportstick

I must admit I do not understand your approach. If the A/C gets too cold, why not just raise the temperature dial to a comfortable level? The recirculation function is used to cool the compartment faster by taking already cool air in the cabin and re-cooling it further instead of the task of trying to cool outside air. This is what happens if you use the MAX COOL function. It is not meant as an ongoing setting, but rather a temporary assist (it also works if passing through a dusty area or behind a smelly truck to minimize outside air blend). It should not be kept on for long periods, as you are increasingly breathing the same recycled air versus bringing in fresh air.

SEC1939

If you hold the recirc button it will close all windows and sun roof. It does this to make it easy if you are in a tunnel or a dusty place. One button does it all.

Kind of nice aye

06e320cdi

When it auto mode it will switch from fresh to recirc or blend the two without you touching anything. Turning off the AC is in fact the wrong approach, as sportstick stated, just turn up the temp or lower the fan speed. If it continues to get too cold, you might need a new evap temp sensor.

jcat

Um...almost every single benz has a cabin filter, most with activated charcoal. Recycled yes, unfiltered though, certainly not.

And I'd love to see a purple and orange zebra! What on earth does your post have to do with the OP's concern?

^^

Ichabod

"And I'd love to see a purple and orange zebra! "






25 sizes bigger than an a-bra.

Sportstick

So, we agree that neither of us claim it is unfiltered! No need to hesitate! The gaseous composition of recycled air is different and less desirable than fresh, and at some times of the year will lead to fogging of windows due to excess humidity from human sources. The OP's issue is best addressed by simply adjusting the temperature control and leaving the recirculation feature alone, unless dealing with need for rapid cooldown or in an adverse exterior environmentl, both temporary conditions.

jcat

jcat

yes, however in terms of doing so with the AC on, the air passes through a condenser/drier system anyway thus eliminating that which you refer to as 'excess humidity from human sources'.

So, in effect, we're both "kind of right". The recirc, however, is the number one way to increase your a/c system's efficiency. Couple the activated charcoal with the drier and I don't think you'd see much difference in air quality from filtered fresh air.

maxi13

Just out of curiosity: are you saying that the oxygen content is the same in fresh air and in the air that is going to be in the car with an alive (breathing) driver with a Recirc on?

The recirc is turned off automatically to protect the driver from getting asleep due to the low oxygen level. This is written in Owners Manual

WEBSRFR

As it should be. Unless the air outside is bad or it is a very hot day and you are trying to cool the car, it is not a good idea to drive around with the climate controls set to recirculate air. No amount of scrubbing or filtering the air can restore the levels of carbon dioxide that will build up as oxygen gets depleted.

Also people should use the automatic climate control systems available in our cars. A lot of thought has gone into them with temperature and even sunlight sensors. Just set the desired temperature and leave it on auto. Unless I am mistaken, there is a sensor that detected if the air outside is bad and automatically switches the car to recirculate air for a short while.

jcat

you guys honestly believe that mercedes engineers would allow the recirc option to seal you into a CO2 cabin of doom? Seriously?!

NO recirc system on any car ever completely seals off the outside air. SOME outside air ALWAYS gets in, regardless of the car. Why do luxury cars seem to be better? Because ALL the air going into the cabin goes through the cabin filter.

The recirc may be on a timer, that's one thing. But I (at 6'2" and 240lbs) certainly put out more Co2 than a 5'4" female that weighs 90lbs. So while the recirc shutoff (if it even works the way you say it does) may correct the air quality for her, what happens when my much higher Co2 output overruns that?

This discussion is in the weeds as far as what the OP posted...I'm shocked we're talking about oxygen contents in a conversation about an HVAC setting in our cars...

Sportstick

Perhaps you are employing the old debate tactic of taking the other side's position to the extreme in order to discredit it? No one here mentioned being sealed in a "cabin of doom", as the blend is likely 80/20. The issue was the shortcoming of the OP's process of switching to recirculation with A/C off as an alternative to a cold cabin, instead of merely changing the temperature setting. MB itself, in the Owner Manual, indicates the short-term purpose of the recirculation function, and the underlying issue is the increase in humidity and deterioration of the air quality, not to lethal levels of course, but sub-optimal.

jcat

See below:

^^This is the statement I was referring to. You would have to be sealed off from fresh air for a LONG time in the context of a car interior for a person to pass out. Much longer than it'd take for the exhaust's carbon monoxide to knock you unconcious.

Sportstick

We agree again! The issue is not losing consciousness...no need to go to that extreme...it is comfort, optimal alertness, and glass clarity (recall the OP turns off the A/C when he uses recirculate).

jcat

the point I was rebutting (which by the way wasn't even your own statement) stated that the recirc shuts off to prevent losing conciousness, which I stated was a complete and total farse.

If that's what you mean by 'we agree again' then I suppose that's true. Otherwise, I haven't the slightest idea what you mean.

Sportstick

We agree that it is unlikely that anyone actually will lose consciousness in a moving car due to the recirculation function, as the minimum blend is typically 20% outside air. However, they may be even subtly affected/fatigued by the gradual loss of outside oxygen levels, which is undesirable. I did not see anyone post their opinion to the contrary, although one poster quoted the Owner's Manual. So, back to the OP...when you are too cold, instead of switching off AC and using recirculation, just turn up the temperature and save recirculation for rapid cool down, dusty roads, or smelly vehicle exhaust ahead.

WEBSRFR

Why are you quoting me to disclaim something I never said? I never said someone is going to die in a cabin of doom. I just said that the CO2 levels will probably go up if you recirculate the same air. You might not die from it but it is probably not ideal as Sportstick has already tried to explain to you. I don't understand what you are arguing about honestly. We are all just trying to help the OP to use the automatic climate control system as it was intended to be used.

jcat

I also never said that it would kill you. But your claim that if the recirc is run for too long that it could cause someone to go unconscious is ridiculous. You did say exactly that, by the way.

Bottom line, by the time the recirc causes you any issues it'll be the exhaust gases from sitting with the car running that will get you long before you breathe yourself out of oxygen. No need to spook the OP. Accurate information is important, especially if your outlandish claims were to push the OP to bring his car in for a diagnostic, which we all know is far from cheap.

merc300

Jcat ; dont back down, you are correct about MB forcing the air recirc off.
i was kinda surprised (well not really) on the number of loyalists that believe in that you need fresh air after just 5 minutes of being recirculated. they really believ after 5 minutes, there is a risk of getting diizzy, not as alert ?
i would not care if it was a 1 hour recirc shutoff (even though i dont believe in it), but 5 minutes - totally wrong.

youngphotons

Hi I am new to MB but I am battling a foul smell from the AC system which is very well documented here as mold issue arising from wet evaporator coil. While I was experimenting with this problem, I noticed that the damper does not respond to "Recirc" button during Manual mode. I understand that computer figures out how much the damper opens up when its' in AUTO mode, but why can't I not control this under manual mode? What is the purpose of having this Recirc button if I can't control it? If I can drive with damper open, I think I can help prevent the mold growth in the evaporator coil. BTW, I went to the dealer and they were no help.

Plutoe

You really need to read the owners manual for your car---everything is clearly spelled out especially the recirc function!!

If you do not have a manual take a trip to the dealer and get close to a woman service writer who will be pleased to explain the function to you!!

Mikey55

Actually I am a new user and appreciate what the user said about the holding of the recirculate button. I would not of known otherwise. Just because you dont think his information is relevant doesnt mean others feel the same. This site after all is for everyone.