HVAC "Auto" Setting
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Joined: Oct 2012
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2026 GLC300 4Matic (X254)
HVAC "Auto" Setting
I notice if it is 80+ degrees outside, and I have the car HVAC setting to AUTO at 70 degrees, the fan doesn't really come on in a meaningful way to blow cold air out of the vents. In my other MBs, that much of a temperature differential would make the fan come on noticably to get the car to 70, then ramp down.
If I hit the temp down to 65, the fan ramps up and cold air starts blowing a lot. Fresh Air or Recirc doesn't make a difference. Is there some sort of calibration or other setting I could be missing?
Thank you.
If I hit the temp down to 65, the fan ramps up and cold air starts blowing a lot. Fresh Air or Recirc doesn't make a difference. Is there some sort of calibration or other setting I could be missing?
Thank you.
Last edited by spyked; Mar 31, 2026 at 06:31 PM.
Out Of Control!!
Joined: Nov 2018
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From: San Francisco Bay Area
2019 C63CS
Are all zones at the same temperature, including the second row and is the rear zone on Auto as well? I've experienced something similar in other cars when the zones were at different temperatures. Zoned climate control in a car doesn't really work. Air doesn't care about the difference between the driver's zone, passenger's zone and rear passenger zones in such close proximity w/o walls separating the zones, so all you get is basically an average temperature between all the zones. So make sure you don't have the rear seat area set to a higher temperature or a manual fan speed. Basically make sure all your zones are synced.
Last edited by superswiss; Mar 31, 2026 at 06:45 PM.
Out Of Control!!
Joined: Nov 2018
Posts: 11,400
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From: San Francisco Bay Area
2019 C63CS
I see. I did actually experience something similar as you described in a C300 loaner. I'm not really sure what was going on, but it seemed that it wasn't really in Auto mode despite saying so in the UI. I took it in and out of Auto a few times and eventually it started to blow air properly. Now this was back in 2022 or so, so early version of the software. It had all kinds of bugs, but unfortunately MBUX is still kinda buggy to this day.
Last edited by superswiss; Mar 31, 2026 at 08:03 PM.
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2026 GLC300 4Matic (X254)
I don't know if this makes sense, but I wonder if the interior temperature sensor needs calibration? Maybe the car doesn't think the interior temp is as high as it really is, therefore it doesn't ramp up fan speed as much as expected. I'll eventually take it in I unless it fixes itself.
Out Of Control!!
Joined: Nov 2018
Posts: 11,400
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From: San Francisco Bay Area
2019 C63CS
Well, one thing you left out is what is the actual temperature in the cabin? You are expecting the air to blow strong based on the outside temperature being 80 and the HVAC set to 70, but the outside temperature doesn't really matter. What matters is the difference between the current cabin temperature and the set temperature on the HVAC. The system does also have a sunlight sensor, so the airflow is turned up if the sun is strong and turned down if the sun goes away like on an overcast day or near sunset.
There are a few objectives the system is trying to balance. Blowing the air hard is noisy for example, so turning down the fan reduces cabin noise while not necessarily compromising the cooling. Rather than using the fan speed as an indicator, what ultimately matters is does it cool down the interior to the set temperature in a reasonable amount of time? As long as the system appears to be cooling down the cabin, a dealership will likely say that it works as designed. In my example of the C300 above, it was actually failing to keep the cabin comfortable. The speed of the fan wasn't what got my attention, but I started to get hot and it felt the HVAC wasn't cooling the interior sufficiently.
There are a few objectives the system is trying to balance. Blowing the air hard is noisy for example, so turning down the fan reduces cabin noise while not necessarily compromising the cooling. Rather than using the fan speed as an indicator, what ultimately matters is does it cool down the interior to the set temperature in a reasonable amount of time? As long as the system appears to be cooling down the cabin, a dealership will likely say that it works as designed. In my example of the C300 above, it was actually failing to keep the cabin comfortable. The speed of the fan wasn't what got my attention, but I started to get hot and it felt the HVAC wasn't cooling the interior sufficiently.
Last edited by superswiss; Mar 31, 2026 at 09:10 PM.
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Joined: Jun 2022
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From: SFV
2025 C300
I notice if it is 80+ degrees outside, and I have the car HVAC setting to AUTO at 70 degrees, the fan doesn't really come on in a meaningful way to blow cold air out of the vents. In my other MBs, that much of a temperature differential would make the fan come on noticably to get the car to 70, then ramp down.
If I hit the temp down to 65, the fan ramps up and cold air starts blowing a lot. Fresh Air or Recirc doesn't make a difference. Is there some sort of calibration or other setting I could be missing?
Thank you.
If I hit the temp down to 65, the fan ramps up and cold air starts blowing a lot. Fresh Air or Recirc doesn't make a difference. Is there some sort of calibration or other setting I could be missing?
Thank you.
I almost always keep my fan on speed one since I don't like to hear it or have it blow in my face. On hotter days, I'll ramp it to 3.
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Thread Starter
Super Member
Joined: Oct 2012
Posts: 583
Likes: 24
2026 GLC300 4Matic (X254)
Seems like it was OK today. But it was hotter outside today. In fact, I had to turn AC up to 72 to get it to not freeze me out. Good "problem" to have I guess. I feel like all my other MBs also made fan adjustments on AUTO setting in a more obvious way. But again, worked like I expected today so who knows. Case closed for now.
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Thread Starter
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Joined: Oct 2012
Posts: 583
Likes: 24
2026 GLC300 4Matic (X254)
