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2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
Originally Posted by Jolida
...Sevice engineer says: "there is not enough Torque speed upon Diagnosis and that the AC is loading the Engine where there may be a possible leak in the fuel injector"
translation: service has no clue what he's doing and is trying to baffle you with BS.
I have a W212 which I have been using since the past 3 years and have been very happy about the performance. It's a 2012 model. Lately it has been having a problem where the Transmission does not shift normally while using the AC. With the AC turned off, the transmission shifts flawlessly and smooth at 1500RPM from the 1st gear upwards and feels just about right as I have always been using it. But lately with the AC turned On, it feels like the car has to force itself to change from the 1st to the 2nd and 2nd to the 3rd gear and so on till the RPM reaches around 2200. On a normal traffic day, it gets very annoying as the car is mostly stuck up at the 2nd gear most of the time and I really have to speed up quite a bit to force itself to change the gear up. On turning off the AC, the problem immediately goes away and the transmission is smooth and flawless. Have even tried doing a transmission reset by turning the key to position 2 and pressing the gas pedal all the way down for like 30 secs and then the rest of the procedure but to no avail. Any suggestions would be very helpful.
Hi
I would like to ask you if you have found a solution to your problem? I'm having the same problem and I haven't found a solution.
OK, so I've been told a few things related to this. Firstly, the MB transmission cooling depends on the speed, rpm, of the input shaft - this is because the pump is driven by that shaft and it is the pump that circulates the fluid through the radiator. So for a given vehicle speed operating the transmission in a low gear improves the cooling. This effect is most noticeable with the larger engines as they tend to spin the transmission input slower as they have more torque. When the smarts see the AC is on the system becomes even more conservative about cooling the transmission and switches to lower gears earlier. Having said the above this doesn't mean that you don't have a bad sensor, telling the transmission is hotter than it really is, or that indeed your shifts are rougher than they should be but I think the logic behind raising the RPM to change up is expected.
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
OK, so I've been told a few things related to this. Firstly, the MB transmission cooling depends on the speed, rpm, of the input shaft - this is because the pump is driven by that shaft and it is the pump that circulates the fluid through the radiator. So for a given vehicle speed operating the transmission in a low gear improves the cooling. This effect is most noticeable with the larger engines as they tend to spin the transmission input slower as they have more torque. When the smarts see the AC is on the system becomes even more conservative about cooling the transmission and switches to lower gears earlier. Having said the above this doesn't mean that you don't have a bad sensor, telling the transmission is hotter than it really is, or that indeed your shifts are rougher than they should be but I think the logic behind raising the RPM to change up is expected.
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
Peter
I am facing the same issue with my W212 CDI which is a 2012 Model. The issue comes at the start if the AC is switched on. Also noticed in the summer when outside temp is about 32Degree C. The issue comes in the initial 1st few KMs that the RPM shifts gears at around 2200 - 2400 RPM as against 1800 - 2000 RPM (with AC off). The interesting thing in common (as mentioned in the thread above) is that after driving a few KMs (~ 1-2 KM) with the AC on, things get back to normal for the Transmission and it shifts normally at 1800 to 2000 RPM. So noticeably this issue is coming in the extreme summer temps, however would like to know from the forum if something needs to be checked as I am also a person, like all enthusiasts here, who would need to know if something needs to be checked/corrected on the car.
I am facing the same issue with my W212 CDI which is a 2012 Model. The issue comes at the start if the AC is switched on. Also noticed in the summer when outside temp is about 32Degree C. The issue comes in the initial 1st few KMs that the RPM shifts gears at around 2200 - 2400 RPM as against 1800 - 2000 RPM (with AC off). The interesting thing in common (as mentioned in the thread above) is that after driving a few KMs (~ 1-2 KM) with the AC on, things get back to normal for the Transmission and it shifts normally at 1800 to 2000 RPM. So noticeably this issue is coming in the extreme summer temps, however would like to know from the forum if something needs to be checked as I am also a person, like all enthusiasts here, who would need to know if something needs to be checked/corrected on the car.
As I said, This is normal, but MB set poit switch delayed for comfort aircon for passenger.
As picture I've take, This is 2 delayed poitswitch - that mean delay shift for max cooling on summer and for heating in cool wheather.
And yes, you can disable it via coding. Try Vediamo or some reader can code your HAVC. Good luck.
Realized my car (2017 C 43, M276.823) is doing this exact same thing as well, the transmission refused to shift until 2K RPM no matter how feathered the throttle is when a/c is on as soon as temperatures outside reaches 30°C (or 86°F), the transmission also quickly downshifts with moderate braking or even with no braking just off throttle, I guess so it can keep the RPMs high?
Once outside temperatures drops below that, it is back to normal within 20 or 30 minutes. Turning off a/c also immediately restores the normal shifting (shifting at 1.5K RPM and quickly reaching ninth gear). I am surprised it never occured to me over these years I had it since new or maybe I never noticed or paid attention. Had ATF done a year and half ago.
So question is: this is meant to protect the transmission? Or engine? Or both?
Thanks : )
Last edited by W205C43PFL; Jul 29, 2024 at 11:37 PM.
The problem that I had mentioned above still remains the same. Since the AC was leaking refrigerant, I recently got the Evaporator coil changed. The problem has gotten worse than it used to be. The car revs high when the AC is switched on and holds on to one gear almost twice the time that it actually needs to. It's like me driving a manual transmission car and purposely holding on to one gear without upshifting.
From the 1st to 2nd gear, and from 2nd to 3rd i have to drive much faster than needed. Thr moment the speed drops even a little bit, it downshifts two gears lower, which is totally wrong by any means. When thr AC is switched off, the transmission shifts like a brand new car.
After the Evaporator coil was changed, the AC intermittently stopped cooling. Upon diagnosis, it was seen that the Compressor had a bad Solenoid valve which needed to be changed. The Cooling is fine since then, but the gear shifting is driving me nuts.
Play with temp settings...
Code feature off with LAUNCH (Xentry can't do this)
I tried to change the temp settings on my drive back home. Went from LO to all the way till 25°. No change whatsoever in the transmission shifting. Have requested a service engineer to get the LAUNCH scanner tomorrow. Hoping to change the setting you suggested to see of it works for my car.
I tried to change the temp settings on my drive back home. Went from LO to all the way till 25°. No change whatsoever in the transmission shifting. Have requested a service engineer to get the LAUNCH scanner tomorrow. Hoping to change the setting you suggested to see of it works for my car.
SHORTCUT....
You can also shut OFF the whole climate control to see if your tranny shifts differently.
Then you'll know if these modules are interacting.
Last edited by CaliBenzDriver; Jul 3, 2025 at 04:10 PM.
Thank you for your reply. From what I understand, i could either
1. Set the cabin temperature manually to say 19° or so
2. Use Xentry to code the above Menu item to " No"
Is that correct ?
Just had a service person get the Launch and changed the setting which you had suggested. The transmission shifts perfectly now. Cant thank you enough. Really appreciate your time and expertise in the subject.
Just hoping that there is no downside to this setting.
Just had a service person get the Launch and changed the setting which you had suggested. The transmission shifts perfectly now. Cant thank you enough. Really appreciate your time and expertise in the subject.
Just hoping that there is no downside to this setting.
Your welcome.
In addition for the same price...
aircon system has a similar setting for heating in winter to "warm up faster" by holding shift Rpm.
It's located right next to the cooling setting that relieved your A/C Rpm troubles.
Last edited by CaliBenzDriver; Jul 4, 2025 at 03:53 PM.
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AC On RPM higher for Initial 1-2 KMs in Summer
