AC Stuck in recirculation mode
Thread Starter
Junior Member
Joined: Jun 2025
Posts: 23
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W211 E500 4Matic
AC Stuck in recirculation mode
Hi everyone,
W211 E500 2004
Another weird issue from me. My AC isn't blowing hard enough - freon level is good, no issues come up when I scan with Xentry. However I noticed whilst checking the cabin air filter, that the recirculation flap stays closed. When i toggle it open with Xentry it opens as it should, but as soon as I disconnect Xentry, restart the car and run the AC - the stupid thing closes!
Now I thought it might be some kind of safety feature when the bonnet is open, but it's not the case because I trigger the hinges to "trick" the car that the bonnet is closed, but no luck.
I've heard that the air pollution sensor can cause this, so today I got a junkyard one and the issue persists.
Where else should I look? Is there a place where I can monitor what the data that the sensor is putting out?
Would be happy to be given any pointers.
W211 E500 2004
Another weird issue from me. My AC isn't blowing hard enough - freon level is good, no issues come up when I scan with Xentry. However I noticed whilst checking the cabin air filter, that the recirculation flap stays closed. When i toggle it open with Xentry it opens as it should, but as soon as I disconnect Xentry, restart the car and run the AC - the stupid thing closes!
Now I thought it might be some kind of safety feature when the bonnet is open, but it's not the case because I trigger the hinges to "trick" the car that the bonnet is closed, but no luck.
I've heard that the air pollution sensor can cause this, so today I got a junkyard one and the issue persists.
Where else should I look? Is there a place where I can monitor what the data that the sensor is putting out?
Would be happy to be given any pointers.
Thread Starter
Junior Member
Joined: Jun 2025
Posts: 23
Likes: 0
W211 E500 4Matic
Just to add a little context, when I say that the flap stays closed, it's the flap that is visible when the cabin air filter is removed. As soon as I run the AC, I can see the flap closing. As a result my AC doesn't blow as hard as it should.
Thread Starter
Junior Member
Joined: Jun 2025
Posts: 23
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W211 E500 4Matic
OK, further edit.
After I used another air pollution sensor from a junkyard car, I verified that the sensor wasn't the issue.
When I went into the actual values of this sensor using Xentry Open Port, the sensor was showing some values, but at the bottom it showed Air Quality - CLEAN. To verify even further, I coded out the option for the AC recirculation to be controlled via the air pollution. After a restart, the flap was still closing as soon as I run the AC.
I also ran a test of all the flaps in the HVAC and they are working as expected.
What's worth to mention is that when I press the windshield defrost button, even when I run the AC on cold, the flap opens.
What else could control this recirculation flap?
After I used another air pollution sensor from a junkyard car, I verified that the sensor wasn't the issue.
When I went into the actual values of this sensor using Xentry Open Port, the sensor was showing some values, but at the bottom it showed Air Quality - CLEAN. To verify even further, I coded out the option for the AC recirculation to be controlled via the air pollution. After a restart, the flap was still closing as soon as I run the AC.
I also ran a test of all the flaps in the HVAC and they are working as expected.
What's worth to mention is that when I press the windshield defrost button, even when I run the AC on cold, the flap opens.
What else could control this recirculation flap?
Last edited by dnikolov-211; Jul 4, 2025 at 07:46 AM. Reason: further info to add
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Joined: Oct 2019
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From: Colorado
G550
These intelligent climate control systems that are supposed to maintain idyllic thermal conditions baffle me. I had a Lexus that would, upon startup, switch to A/C recirculation on a hot summer day when the car's interior temperature was 30F above the outside temperature, apparently believing that venting in cooler air was a stupid idea. So I would roll down all the windows. Conversely, in the winter turning on the heat upon startup would draw in frigid outside air apparently so that carbon monoxide wouldn't accumulate during warmup. It's hard to say if your problem is a malfunction or is the way it's designed to work.
Thread Starter
Junior Member
Joined: Jun 2025
Posts: 23
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W211 E500 4Matic
These intelligent climate control systems that are supposed to maintain idyllic thermal conditions baffle me. I had a Lexus that would, upon startup, switch to A/C recirculation on a hot summer day when the car's interior temperature was 30F above the outside temperature, apparently believing that venting in cooler air was a stupid idea. So I would roll down all the windows. Conversely, in the winter turning on the heat upon startup would draw in frigid outside air apparently so that carbon monoxide wouldn't accumulate during warmup. It's hard to say if your problem is a malfunction or is the way it's designed to work.
Moreover, I did cool the car down significantly by letting the AC blow for 30 minutes with all the windows closed and yet the recirculation flap stayed closed.
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