cloudz949

I have 3 zone climate control option with my 2012 GL450. I noticed the rear AC would be turn off sometimes when I start the car. Other times, the AC will remain turned on as the previous setting. I looked in the manual but couldn't find the info. Does any one know if there is a control or special behavior that would toggle the rear AC setting. Thank you.

CloudZ

carpersn

Unfortunately, the bean counters at MB really downgraded the 3-zone control unit at some point since 2007. My '07 has the digital unit for 3-zone and I can not only control the third zone but it remains set until changed again (turning off and on doesn't effect). My '12 has 3-zone with what looks like the same front controller as a non-3-zone-meaning I can't get it to change temp for back at all from the front unit (despite what the manual alludes to). Then whatever setting seems to change at random when the car is restarted.
But of course, the Canadians apparently still have the original unit?!

lotuni

Yep. My 12 has the digital 3zone and can control the back fom the font. Odd why they would remove it in the US version.... Was it some kind of option in the US?

JimBarnhart

I recently had to figure this out when ordering my 2013. I'm not positive I have this right, but here's what I think is the situation. There are 3 scenarios for what is installed in the back of the center console. 1) nothing, 2) a simple control unit and 3) an advanced control unit.

3) is the 3-zone climate control and has fan control, temperature control, ability to have air at the feet or the head. 2) is what you get if you order heated rear seats without 3-zone. It has a simpler dial, one that doesn't allow temperature control. I believe it does allow for some fan control and some direction control, but I'm not 100% positive. 1) is if you don't have either heated rear seats or 3-zone and then it's just a finished covey hole.

BVLDARI

So is the consensus that the rear AC can not be controlled from the front? I too read the manual which in my opinion clearly states that the rear AC can be synchronized to be the same as the front?

jakeg104

I just picked up a '12 gl550 and it looks to be the same as described above, which is no way to control the rear temps from the front, as well as a lack of 'mono', both of which were available on the '07 gl450 we traded in.

Mono syncs all temps to the driver control.

Has anyone figured out how to control the rear ac temp from the front yet?
Thanks!

Bimmer777

I just picked up 08 320CDI. I have Mono button and driver's knob controls all three when Mono is depressed.

lotuni

It can definitely be controlled from the front. From the manual p139 (2012)
-sorry for the text only copy paste. Symbols and button pics are missing but you'll get the point.

USA only:
X To increase/reduce the rear- compartment temperature using the front control unit: turn the SmartKey in the ignition lock to position 2.
X Press the REAR button.
X Turn control C clockwise or counter-
clockwise (Y page 136).
Only change the temperature setting in small increments. Start at 72 ‡ (22 †).


Canada only:
X To increase/reduce the rear- compartment temperature using the front control unit: turn the SmartKey in the ignition lock to position 2.
X Press the button.
The display changes to rear-compartment climate control.
X Turn control E clockwise or counter- clockwise (Y page 136).
Only change the temperature setting in small increments. Start at 72 ‡ (22 †).
i To return to the standard display, press the Y button.
i The rear display changes to the standard display automatically after three seconds.

BVLDARI

just tried it again - still doesn't work....

my tech says it is not supposed to work - need nicer display unit that the early cars had in the US and Canadians got for the rest of the run. Why on earth did MB cheap out on the AC on a $90k vehicle is beyond me...

Bimmer777

This is what the controls look like on my 08 320. You press the rear button and can turn the passenger side knob to control the temperature in the back.

BVLDARI

yep, and then for some unknown reason they decided to cheap out and stopped offering this control module / display all together in the US....

Bimmer777

I am in the US and mine is a 2008. So, I am not sure at what point they started offering different unit.

BVLDARI

my guess would be 2009 based on what I just saw on ebay...

Bimmer777

Ventilated seats!!! Would love to have those.

Yes, I see what you mean now.

lotuni

yes, mine is the same except in Canada mine has a symbol of the seats with an arrow pointing to another seat (ie front to rear). I'm sure they used symbols because in Quebec the text needs to be french, to typically they use symbols to make it generic so they dont have to use any text and will work for English and French.

You guys without the display, do you have the center defuser mounted on the roof above the second row?

As I understood it was only truly a 3 zone climate control if you have the diffuser mounted above the 2nd row and only if you had that would you get the climate control with the display and the "REAR" button.

BVLDARI

Are these the vents you are talking about? If yes, then yes, I have them.

lotuni

yes, exactly!

In Canada at least, if you had the 2nd row airvents, you had the display in the HVAC controls.

Is that not the case in the US? Does someone have the 2nd row upper vents and not the display control? If that is the case then that is weird on MBs part. Does not make sense.

BVLDARI

It appears that after 2008, in the US, they got rid of the front display unit all together (regardless of model). There is a reference in the manual on how to control the rear climate control from the front with the "basic" unit but as far as I can tell - these instructions do not work.

dougpark464

I have the same problem. I usually reach over to the back to adjust (my kids are in car seats) which is a pain.

Has anyone checked to see if you can replace the unit with the older digital version? I'm assuming you can buy the 2008 part at the dealer or ebay.. But the question is if the connectors have changed.

BVLDARI

FYI, I have a call into MBUSA. Will advise you guys once I talk to them.

jakeg104

Same here, it's a pain and sucks to know that our older car was more feature rich. It also seems like the front windshield IR glass on the '12 is less effective than the IR glass on our older '07. My wife commented on it as well, saying that her hands feel warmer in the new car. Really disappointing.

Another option would be to source the Canadian control unit from a '11 or '12 and see if it works?

Awesome, looking forward to a positive response from them!

dougpark464

We have the IR glass option on our '11 and seems to work well but we don't have baseline comparison with an older model. I looked at the special order list for the new '14 model and IR glass is no longer an option which is disappointing..

jakeg104

So been doing some research on these control units. I found a few canadian GL's online for sale, took their VIN number and searched on EPC startke and ased on this info, the canadian models come with the following Heating and a/c control part number-

A2519000401

Below is a picture of what this controller looks like. Per the mercedes manual, page 136 shows this to be the Canadian control unit that has Mono as well as rear control accessibility from the front-


Also, the rear controller that came with this particular car is part #
A16490663009174

Now, my car is a '12 GL550, and the parts that I currently have are:
A2519000501- US front control unit
A16490665009174- Rear AC control unit

I've bolded/underlined the part number difference. They all have the same connector in the back as far as I can tell, based on looking at numerous controllers online and eBay.

I found a used Canadian control unit from a salvage yard for $500.

Question is, if i were to source these Canadian parts, would they be plug and play? Meaning, would there be an issue of a different harness being used in Canadian vs. US cars?

Would it make sense to call the parts dept at the dealership and ask them if these parts are fully interchangeable?

lotuni

I don't know the answer to your question, but that is exactly my control unit!

I wonder why MB did that. It would also not seem logical that they would have to manufacture (or source) 2 different control harnesses.... I wonder what non North America units look like? Auto manufacturers want to has as many common parts as they can regardless of geo.

I don't know about in the US, but in CA (Canada not California ) if I go a to a dealer and ask about anything even remotely close to a "difference between US and CA in parts" they get all defensive and "wont work", "void warranty", "wont honour it", "cant order it". They just don't know how or even want to deal with it.

BVLDARI

It took literally 4 months for MB to get around to giving me an "official" answer. This has left a bit of a bad taste in my mouth but here is the answer:

"The only means of temperature adjustment for the rear from the front is if the front HVAC controls have the second "person" icon. I have verified that this isn't something that is offered for the 2012 GL-Class in the US."

This is very disappointing to me for multiple reasons but primarily:
1. The MB Original Owners Manual explicitly states that you can control the rear in a 2012 vehicle even without the second person.
2. A $20,000 Dodge Caravan can control its rear seat climate control from the front (and a $91,000 MB cannot).
3. I have to literally take my eyes off the road to adjust this.

MBUSA also stated that retrofitting the Canadian climate control is not exactly an option and is more involved than just swapping climate control units.

Finally, I am still waiting on answers as to why my rear climate control resets back to 72F even if the car hasn't spent 4 hrs off and why the rear climate control shuts off by itself randomly.