2007 ML350 - AC just stopped working, but the fan went on high. Went to have it checked and was told that there was an obstruction on the system and Compressor no good. So I replaced the Compressor, Dryer, Expansion Valve, AC Pressure Sensor, Ambient Sensor and replaced all seals. Did a 2 hour vacuum, let sit for 1 hour to see if had any leaks. But when I'm trying to charge the system, after the 2nd 12 oz can, it doesn't want to accept any more refrigerant as it seems that the Compressor is not activating. Checked the voltage and there's only 4.2 volts. -So- is there anything that signals the compressor to activate? I replaced the Climate Control Switch w/another used one to check, but still all the same. Any suggestions? -Thank you- Manuel

 

Manny, when there is a problem in the A/C system, the A/C Control Module will prevent the compressor to operate. The code/s must be read to see what the problem is.

After replacing the component, according to the code #, the code must be erased and then the A/C compressor will then be operated.

You must own your own scanner for this problem and any other future problem that you might have.

 

Thank you Sir for your response and as always been very helpful.
I did erase all the codes, but still having the problem.
Is it the A/C Control Module which send the correct voltage to the Compressor? Do you happen to have an electrical diagram of the system?

 

What is the brand of the compressor you installed?
AFAIK some brands (other than OEM, DENSO) will not start up and you need to modify it. I read it somewhere on this forum.

 

What was the code number that made you replace the compressor? And what were all the codes that you erased?

You believed this mechanic who said there was an obstruction and now you want to tinker with the system.

Post your vin# for proper A/C system.

 

VIN: 4JGBB86E57A257689
Unfortunately since I erased the codes, I don't know the number of the codes, but it did mentioned the compressor and ambient sensor and pressure valve.
Honestly I think is the Computer that governs the system, because even though I have no codes now, it's malfunction is just as before replacing all the components with OEM from FCP Euro.
So I'll would like to see it's electrical diagram to follow it's route and diagnose the system, just don't know if it's governed by the SAM (front or rear) or the ECU, etc.

 

Here is the diagram.

 

Thank you for all your help. Verified the system again, checked the diagram.
Unfortunately the truck began to give me misfire at startup again, after a huge Engine tune investment and also the Fan going on high right from startup (engine cold and w/out turn on AC which still not working). I made some calls to some MB shops, and they've all suggested that the ECU is the one causing all of this malfunctions.
So I sent my ECU for cloning on a new OEM re-manufactured at Precision ECU. Will update you'all after it returns to see if it fixed the nightmare.