Air Conditioning fault (6 years and counting)

[Uberwagon]

So a bit of history.

I have a 2006 ML500, earlier 5.0 V8.

A long while back the air-conditioning started having issues. It would be fine and then suddenly turn off. I’d Rev the engine in neutral and it would come back.
The problem got worse and at the time I had a Mercedes warranty with it still. They told me
It was low gas, then said it was too much gas, then said all modules are fine, then said compressor was faulty.

When they said the compressor was faulty there were no codes and the warranty had now run out. The AC started working again and it has been intermittent for the last 60,000 miles.

When it kicks in the AC is ice cold, it has been regarded twice since I was told the compressor was at fault and it has always held gas.

Now it shows a 9006 AC Short Circuit fault but not all the time and it does clear itself.

More reading brings me to people who have replaced the AAC control module, the compressor, Earth and Power checks and the fault is exactly the same.

The fault was fixed by updating AAC control
Module software from 2514420405 to version 2519022200. This is in the US.

I’ve rung up 2 Mercedes dealers today and the first said no we will read the codes and get back to you, the second said the car is too old for it to be a software issue and it won’t be it.

I just want to make sure I have the right software version as I don’t want to be throwing parts at the problem without checking everything. It mentions the software in a technical service bulletin.

Can anyone confirm if the AAC module software loaded onto it and if not what else I could be looking at ? It’s frustrating as when manually energising the AC compressor it works perfectly. Today was a 4 hour drive and no issues at all.

Dave!

 

[Duff3103]

A circuit issue would certainly give you an issue as you have described, although id maybe be looking into the control panel on the dash board as there was a similar sort of fault on Mk1 X5 bmw's that the blowers would come on while the car was locked and keys indoors away from the vehicle. Im wondering if this could be a similar fault if the compressor checks out ok as well as the pressure switch and gas level.

The compressor can still be faulty even if it holds gas as it has a clutch mech to allow it to kick in and out as required

It certainly sounds like the wiring to the compressor or controller to it is at fault hence the short circuit. id presume that when the fault is present is when the short circuit is a present fault. Next thing id be doing is to obtain a wiring diagram and test all the wiring from the module to the compressor and other components

Your a/c should be regassed roughly every 3 years also another thing to be aware of

 

[slade1]

My 05 CLK has it's first gas top up a few weeks ago, It's on all the time summer and winter.

 

[alexanderfoti]

This sounds like either a wiring fault or an intermittent suction valve fault in the compressor.

That said, get a proper diagnosis carried out on your car, rather than trying to find another car with the issue and replicating it's repair on yours

A measurement of the suction valve control voltage whilst it's having an issue should narrow it down.

I've had suction valves fail dead short and cause the output in the module to fail, with no fault codes.