DieselDDS

Hi everyone,
I have a 2009 ML 320 Bluetec with 160,000 kms.
I've had it into the dealership 4 times now with an air conditioner issue - The AC compressor will suddenly stop, and the car will blow warm, very humid air. Originally the dealer told me it was a short and it was fixed. The next two times they said it was a faulty ground wire. Now they're stumped.
They claim the compressor works fine. I think it might be a wiring/relay issue. Although it will stop working randomly, it more often fails when I touch something on the control panel, such as decreasing the fan speed, etc. The blower is not the problem. Interestingly, when the compressor quits, you can sometimes hear the blower sound intensify on and off like the AC is trying to start up again. About 1/10 times it's successful.
So far I haven't found a good solution. When they replaced the "faulty ground wire" the system worked for about a week.
For now I'm forced to keep the AC on full cold and with the fan on full speed - but it still quits daily and usually wont restart.
Any ideas?
Thanks all for your advice.

DieselDDS

Pat from Vancouver - your account won't let me send you a private message...

The dealership has worked on the car again with no solution. The first time they told me there was a short in my compressor and they claimed to have fixed it. The second time they called MB head office and were told to replace the grounding wire to the AC compressor. The part was $27 but with installation it was a few hundred dollars.
This summer it's cycling on/off again and the fan surges when that happens. Last week the fan died altogether. Yesterday the fan was working again with the AC system cycling on/off but no air coming out of the two centre vents. I am starting to think this is an HVAC problem.
I'd be very thankful for any ideas if anyone has them.

06e320cdi

Sounds like the evaporator is freezing up. It can happen in very humid weather, along with HVAC filters that are clogged. I had this happen on my CDI. Also, have them check the engine cooling fan and associated relay is working. If the engine cooling fan will not speed up with engine temp, then it will shut off the compressor. I assume, they checked the refrigerant level.

DieselDDS

Thanks for the advice, and I passed it along to my dealership.
The story has only gotten worse...The dealership kept the car for 2 days, and decided that the compressor itself was toast. So they changed the blower (they claimed it was at fault too), the compressor and the dryer on the AC unit - basically an entirely new A/C unit for a few thousand dollars. The first time I started the car when leaving the dealership after paying my bill in full, the A/C started cycling on and off again.
The fan is blowing on full speed, the A/C comes on (ice cold air), then it makes a strange sound (the service manager says its a flap closing), the fan level drops slightly and warmer and much more humid air starts rushing in. After that the system randomly cycles the A/C on and off, with the A/C light staying on the entire time. So basically I've replaced the entire A/C system and it has not solved the problem. I am sure that some obscure other system or circuit is commanding the air conditioning on and off incorrectly.
The dealership still has the car (and has for about a week), and they've filed a request with Mercedes-Benz for help, sicne they're stumped.
Any advice is always appreciated. Thanks all.

2008 ML 320 CDI

Sorry, I don't have any solid advice but I am very interested in your case and would like to know of any new developments.
We have a 2008 320 CDI ML and occasionally the air conditioner won't come on and when this happens, the fan speed will "hunt" up and down on own accord. When the air conditioner does come on, every thing seems to stabilise and cool air is delivered as per the setting on the temperature dials.
I believe it says in the manual that the air conditioner won't come on if the refrigerant level isn't where it should be leading me to think that perhaps the refrigerant level in my vehicle is just at a critical level causing the A/C to sometimes not come on. But now with your pump having been replaced, the refrigerant level would have been brought to spec levels and still your system isn't working properly.
I have also thought that the problem could lie with the cabin temperature feedback signal to the system controlling the A/C unit. If an incorrect temperature signal is fed back to the A/C controls, it would obviously cause problems. Perhaps you could suggest that the dealership check the cabin temperature sensor which the manual shows to be located on the panel where the dials are for setting the cabin temperature.
I also wonder if the COMAND software also controls the A/C functions and whether the software could go faulty. Perhaps a software update would solve the problem.

pacer971

that happens when the torque converter starts to fail (better believe it ) Pretty common problem on bluetec. Computer measures different torques of the engine and the torque converter and shuts off some of the peripheral devices powered by the engine (security feature to protect the engine). AC is the first one. When torques equals it turns ac on again. In some worst cases it can turn off the steering wheel.
So, first check the torque converter. MB Star can diagnose if there is a difference in the torques.

nialaayrus

I'm having the same problems with my ML350. Been searching the net and found two similar cases, but no resolutions. Basically got the code 9006 Air Conditioning Compressor short to ground. Replaced the compressor assembly, problem didn't go away. DieselDDS, what did the dealership come up with?

Maj. Dundee

What made you think that the words "short to ground" meant to replace the compressor? Did you ever consider that it could be a wiring problem, a component other than the compressor, or a blown fuse?

For starters, check fuse #12 in the Cockpit Fuse Box.

After replacing the comp., did you clear code 9006?

nialaayrus

Here's what I did:
I did check the fuse #12, fuse intact.
The AAC control panel is on and responding, hence the 9006 code. I guess I felt that it seemed logical to condemn the compressor at that time.
I also checked wire leading to the compressor control valve (single-pin connector), no short. My next question would be: what other component is controlling the compressor (i.e. the compressor control valve)? Is there any SAM module responsible for handling AAC request? Need some enlightment here. Thanks.

nialaayrus

Maj. Dundee, well it seemed like the most logical thing to do at that time. At first I didn't consider other components, but I did check the wire leading to the compressor control valve (single-pin connector), no short there. Resistance of the control valve around 12Ohms measured between single pin and compressor body, but I don't know what it translates to anyways.

Regarding blown fuse(s), I don't think you'd be getting "short to ground" code, cmiiw. Cockpit Fuse #12 I checked after you suggested, fuse intact... but actually I didn't have to check because AAC panel is on and all buttons respond to press/touch.

So, again I'm getting 9006 compressor short to ground. When the engine and AC turned on, compressor request is at 0% (zero percent), back-probed voltage at the control valve is 0V (zero volt). When I check for voltage again with control valve wire UNPLUGGED voltage is 13++ (battery voltage), compressor request at 100%.

I guess I need to know what other component is responsible for compressor control valve pulse-width modulation. AAC requesting compressor work, but who/what is actually driving/powering it? Is it one of the SAMs? Or passenger compartment blower? Need some enlightment here. Thanks

Maj. Dundee

Please UPDATE YOUR PROFILE in USER CP and indicate if it is gas or diesel.

Maj. Dundee

Post your full vin#.

nialaayrus

It's WDC1641862A079507

Maj. Dundee

Thanks for updating but it is not complete. This might seem trivial to you, but you left out whether it was gas or diesel and where you live.

You do not own a 2007, it is a 2006 so update indicating that year.

Maj. Dundee

One other thing, there is a big difference between SHORT CIRCUIT & SHORT TO GROUND.

Code 9006 says that there is a SHORT CIRCUIT and not STG.

SC means that somewhere along the way the voltage stopped flowing in a wire.

STG means that that same wire has come in contact with ground wire or a chassis ground.

So, it's either you assumed the wrong interpretation or the scanner you are using is supplying the wrong wording.

nialaayrus

I live in Indonesia, and it's a gas engine (272). Ok 2006, it's just that the car was first bought from the dealership in 2007, and registered as a 2007 car, and that's what I was using as a reference. Just like what you guys have stateside: a vehicle produced in 9/06, for example, is/may be called a 07 model. But for the sake of argument, ok 2006.

nialaayrus

Ok, will contact Bosch and let them know they're probably wrong.

Maj. Dundee

Forget about calling Bosch, they will listen to you but they aren't going to make a new update to correct the terminology.

Are you ready to do some wire testing?

nialaayrus

Yeah okay, let's start.

Maj. Dundee

Remove the AAC Control Module (very easy), by removing 2 screws. Pull it out and locate conn. "B" which is the largest connector.

Find wire #26, Violet/Blk. Start eng. and select A/C. Probe the metal contact at wire #26 for12v with a test light or a volt meter.

Regardless of the results, reinstall the AAC Mod.

nialaayrus

OK, backprobed pin #26 of the 28-pin AAC connector (connector B). Started engine, turned on AC. Result is 0 Volt.

Maj. Dundee

Are you are absolutely sure that #26 was Vio./Blk wire and was the blower on and was the negative probe properly grounded?

Remove the AAC again & recheck # 26 wire for 12v. Also check wire #27 BLUE/WHITE for 12v. This is all done with the eng. running and with A/C selected.

After the compressor was changed, did you yourself recharge the refrigerant or was it done professionally?

After the compressor was changed & charged, did you clear code 9006?

Maj. Dundee

Your AAC Module #251820 84 89, was replaced by #251 870 02 89. More often than not, they do this because the previous version was faulty.

So please make sure that all the voltage tests are done with surety.

nialaayrus

OK, I added another backprobe needle at pin #27 Blue/White wire. Got battery voltage with engine running, AC selected and blower ON (see picture above). I got 12V even with engine off, am I correct to assume that #27 is one of the power supply lines? Also, I hope this clears any questions about proper grounding of the negative lead.



One more time, pin #26 Violet/Black wire showing 0 Volt with engine running, AC selected (see yellow circle), and blower ON (three bars on the panel, air came out strong out of vents).
By the way, prior to your leading me to check voltage at connector B, I once removed AAC panel, and confirmed a continuity between pin #26 (Violet/Black) and Blue/Green wire leading to compressor.

I own a european garage - no amateur would pay what I have been paying to maintain the Bosch subscription - did all the wire tracing/check myself, all the compressor work, recharged the refrigerant to spec (according to label under the hood), confirmed that the refrigerant pressure sensor registered around 7 bars at static, and cleared the 9006 code many different ways... 9006 always came back.

Maj. Dundee

Wire #27 is not another feed wire. It is the actuation wire for the Coolant Cir. Pump which runs continuously when the eng. is running and a few minutes after the eng. is shut down. It is working properly.

If everything is in order, then there is no other explanation other than the AAC Module being faulty. You can remove the AAC completely and remove the T7 Torx screws and inspect the board on both sides for any circuit damage.

If you own your own shop, it would be easy for you to borrow an AAC from a junk yard and try it, 84 89 or 02 89.