so recently replaced the shifter lever and put the car back together but now have no heat. ac blows. can control the fan speed but can not control the air vent direction and cant not get heat.

sds shows that all 12 air flap actuators have communication failures. the tech wants to replace the ACC module and see if that fixes the issue. However if it doesnt theres no refunds on the $1200 part.

It seems suspicious to me that between disconnecting the acc unit and reconnecting it that the unit suddenly malfunctioned. Also the fact that all of the actuators are getting communication failures. I tend to lean more to there is a bad connection. either a connector is damaged or something is loose. So my questions are:

1. Does the acc module communicate directly with the vent flap actuators or is there another module in between.

2. Has anyone ran into this exact problem before with the same error codes and replaced the unit and that fixed the issue.

3. in pictures it looks like there is a single connecter / cable that connects all the actuators in series. Does this connector connect to the center console anywhere? If yes where?

4. is there anyway to test the acc unit or vent flaps to verify exactly what the issue is?

any help is appreciated.

 

I would take it apart and make sure you have all the connectors back togather correctly and didnt miss one

 

all the connectors are plugged in.

 

check fuses

 

i have reviewed the fuse chart and do not see any fuses that correlate to the vent flaps. do you know of something specific?

 

can anyone tell me what the center plug in the ACC unit connects to?

 

got a pm the other day about this issue and wanted to provide a final diagnosis for anyone that might experience the same problems. Note this is for a 2003 sl55. The connectors / ports may or may not be the same on latter models.

Also note that i have definitively determined that no special coding is required to utilize an AAC unit from another car. There is however a "Normalizaion" procedure which incredibly most mercedes techs have no idea exists. Even after showing them the Mercedes issued training docs that outline the procedure i got "ive never seen that before and i work on these every day. I dont think thats correct" geez. Anycase the normalization process is not required for an AAC unit to function. However if you do install another unit and you get "wierd intermittent or random behaviors" (not a complete functional failure) then the normalization function is meant to reset these behaviors back to there intended functions.

My specific symptoms were:
blower fan could be fully adjusted.
All buttons on the AAC appeared to be working.
I had A/C but DID NOT have any heat regardless of temperature settings.
NONE of my vent flaps would respond to adjusting the blend functions on the AAC.
NONE of my vent flaps would respond to adjusting the vent flow controls on the center vents.
SDS showed a complete communication failure to all vent flap motors (12 of them)

On the back of the AAC there are three ports. The small 4 pin center port controls the vent flaps.

Ended up that there are two plugs in the console that both fit the back of the vent flap port of the AAC unit. The correct plug had slipped down the side of the console and was hidden from view. Because the plug that i could see (turns out it was just an unused plug from a non installed option on my car) fit into the notched port it never occurred to me that there could be other plugs that fit the same port. The tech says it was just one of those rare instances on the Mercedes where multiple plugs could fit the same port.

Of the two plugs one has a 4 pin brown connector the other has a 4 pin black connector. The black connector is the correct plug.

If you have the black plug connected and all the vent flaps are still failing note that the black plug is actually a two piece connector. one end plugs into the port the other end connects to the ribbon cable. As i have seen from other member posts the part of the connector that connects to the ribbon cable could have been damaged and is not making a secure connection to the ribbon cable.

If you have a damaged connector i have verified with my dealership tech that they can replace just the connector. But its totally up to the dealership whether they will undertake that repair. Most will simply say you need to replace the entire ribbon cable which requires removing the entire dash (about 25 hours of labor). You can buy just the ribbon cable for about $90 bucks and a competent tech should be able to cut and splice the two cables together to fix the borken connector issue.

Hope this helps clear up any issues that others may run into in the future.

 

You can actuate the vent flaps with SDS. That will tell you if they work. With SDS you can also control the fan.

 

The vent flaps can only be controlled via the SDS if the cable has a good connection to the AAC unit.

All sds does is send a signal to the AAC unit to activate the flaps. If the AAC cant send the signal because of a disconnected / damaged cable then the SDS cant do anything other than post a communication error.

 

My answer was in regard to 4. in your original post.

 

ahh gotcha. thought you were referencing the last post i made.

 

Good info. I can add that it is possible for the connectors to the individual actuators to be damaged. I was unable to identify a replacement part number for the connectors. I was able to buy a complete cable assembly (Ebay) complete with actuators for $65. I then moved connectors from the Ebay harness to mine. These are "IDC" (Insulation Displacement Connectors), so they just clamp onto the wire. The used ones were brittle. I ruined 2 but got 2 transferred over successfully. Of course, since then I learned that a brand new harness costs less than $70 at the dealership!

R&R of the dash is a painstaking process, but only difficult in 1 or 2 places. A few pieces of learning there:
- No need to remove the seats.
- Do have the top down.
- No need to remove the steering wheel. Just move it to its lowest and rearmost position.
- Place a jackstand under the steering column where it bolts to the tubular steel subframe. Support it in position before unbolting it from the frame.
- Let the wheel rest on the driver seat.

 

[QUOTE=coldhammer;6290911]got a pm the other day about this issue and wanted to provide a final diagnosis for anyone that might experience the same problems. Note this is for a 2003 sl55. The connectors / ports may or may not be the same on latter models.

Also note that i have definitively determined that no special coding is required to utilize an AAC unit from another car. There is however a "Normalizaion" procedure which incredibly most mercedes techs have no idea exists. Even after showing them the Mercedes issued training docs that outline the procedure i got "ive never seen that before and i work on these every day. I dont think thats correct" geez. Anycase the normalization process is not required for an AAC unit to function. However if you do install another unit and you get "wierd intermittent or random behaviors" (not a complete functional failure) then the normalization function is meant to reset these behaviors back to there intended functions.

My specific symptoms were:
blower fan could be fully adjusted.
All buttons on the AAC appeared to be working.
I had A/C but DID NOT have any heat regardless of temperature settings.
NONE of my vent flaps would respond to adjusting the blend functions on the AAC.
NONE of my vent flaps would respond to adjusting the vent flow controls on the center vents.
SDS showed a complete communication failure to all vent flap motors (12 of them)

On the back of the AAC there are three ports. The small 4 pin center port controls the vent flaps.

Ended up that there are two plugs in the console that both fit the back of the vent flap port of the AAC unit. The correct plug had slipped down the side of the console and was hidden from view. Because the plug that i could see (turns out it was just an unused plug from a non installed option on my car) fit into the notched port it never occurred to me that there could be other plugs that fit the same port. The tech says it was just one of those rare instances on the Mercedes where multiple plugs could fit the same port.

Of the two plugs one has a 4 pin brown connector the other has a 4 pin black connector. The black connector is the correct plug.

If you have the black plug connected and all the vent flaps are still failing note that the black plug is actually a two piece connector. one end plugs into the port the other end connects to the ribbon cable. As i have seen from other member posts the part of the connector that connects to the ribbon cable could have been damaged and is not making a secure connection to the ribbon cable.

If you have a damaged connector i have verified with my dealership tech that they can replace just the connector. But its totally up to the dealership whether they will undertake that repair. Most will simply say you need to replace the entire ribbon cable which requires removing the entire dash (about 25 hours of labor). You can buy just the ribbon cable for about $90 bucks and a competent tech should be able to cut and splice the two cables together to fix the borken connector issue.

———————————————————————————————
8 years later, just wanted to say thanks for posting this issue. I had the exact same problem and reading this post convinced me I missed a connector which is exactly what I did.

 

Well, maybe not quite done yet. If you start the car cold, should air blow out of the vents or should the fan kick only after warm up and then blow hot air? (all my other cars work this way). I do have heat now but the outer vents immediately blow cold air as soon as I start the car. Once the car is warmed up, I am struggling to keep the temp correct. It's either too hot or too cold and "one click/degree" on the temp adjustment seems to make a huge difference either way. So I'm constantly adjusting up/down while driving.

I definitely missed a connector in my post above because I didn't have ANY heat before. I did a scan with my SDS and I have SIX mechanical fault codes for six different flap motors. That doesn't even seem possible and wondering if I missed another connector when I had the radio and center console removed.

Anyone have any thoughts here?

thanks
Bob

 

I had the same issue, searching the forums no luck until I found your post. I bought the car with this problem, so I removed the AAC unit the first time did not see anything wrong. Then I read your post and I removed it a second time to find that the black connector was actually missing and found it at the back of the cupholders!! Connected it and most of my error codes went way.

Thank you for posting.

 

I can't thank you enough, i had same issue after replacing command unit, the brown plug to to the shifter lever unit connected the black ribbon cable to ac control unit and all is well

 

Boy, I will echo the same praises. I bought a 2004 SL 500 about a year ago and immediately had a front right suspension problem that caused the front right corner of the car to hit the ground. It messed up all kinds of things. And I had not even gotten to know the car very well yet. I had had it for less than two weeks! So I’ve been working over the last few months fixing the car. One of the problems was that I was getting no heat and I was getting the 12 fault codes all indicating that the flaps weren’t working correctly. So I thought it was the control unit and I considered ordering another one just yesterday. But then I read this thread and took the console apart today and sure enough there was that loose black connector that was supposed to go into the back of the control unit. It was so obvious. By the way, there was no brown connector.

So many thanks to all that have contributed to this older post over the years.