2002 ML 500 Air Condition Dilemma
 

Hi Team -

Have a bit of an off one for you. I've been having on / off AC issues with my truck for a few months, and now I'm stumped. Long story short:

1) AC was not working (expansion valve leaking, recharge every few months)
2) Expansion valve finally replaced (ac working great for 3 months)
3) AC stopped blowing cold...mechanic says compressor now leaking and not turning on (02's) continuously ran, but this one just wasn't producing cold air hence calling it "turning on"
4) compressor replaced, but no cold air, mechanic stumped

**neither ac pipe is cold
**no noticeable change in rpm when hitting auto button
**have read on the 02's, that the ac is not controlled by the aam so trying to figure out where next to send my mechanic

Any help is greatly appreciated

Have the AAC checked(AAC is controlling the AirCon). Scan the car. You cant keep on changing parts blindly, just because the mechanic said so.
You might have changed the compressor for nothing.......Again, scan the car.
Also after repairs on the AC, one must clear the codes.

The compressor was the original and at 295k miles and leaking badly, so it did need to be changed.

The AAC is the push button module correct?

AAC module is outlined in green.
You really need to scan the car.......

Mech said he did and no codes came back. Is there a way besides checking voltage to check the AAC? It's blowing heat when I say heat, but no cold when I say cold. It seems like it's operating but something just isn't telling the compressor to start cooling

Wayne, if the mech. said that "no codes came back", that means that there were codes originally. So what were they?

Meaning no codes came at all, ever

You need to find someone with a pro level scanner.

Hey guys, very new to forum. I have been reading for about a year so I would know what to expect when things started going south. I finally found this post that sounds in part like my problem. 2002 ML500 155000 miles. AC stopped working all of a sudden. The compressor is not working. Its that type that turns all the time. Gauges indicated that the compressor was not working 100(H) 100(L) no fluctuation. Checked voltage at compressor connection "0"volts. Replaced Temp/pressure sensor & compressor, evacuated/charged the system. Still not cooling, no pwr at compressor. Any help is appreciated!

The first thing to do is check fuse #5 in the right side lick panel fuse box. Probe both contacts on the fuse for 12v.

Turn the key to pos. #2 and feel the Coolant Cir. Pump with your hand. Is it operating without noise?

Post back with results.

I checked the fuse on right kick panel (15amp #5) and it has 12v on top and bottom. With the key turned to pos#2 I do not feel or hear anything from the coolant pump. It is the one located between the battery and right cylinder head?
Thanks for trying to help an idiot!

If the Coolant Pump seizes it burn the circuit inside the AAC Control Module.

Remove the AAC again and this time take it apart, T7 Torx screwdriver necessary, and see if the board is burnt.

If it is burnt, then you will need a new AAC and a Coolant Cir. Pump.

The pump must be replaced first and then the AAC.

I have seen this unit in a ML430 post I think as the possible problem. Can you recommend a source for the pump and AAC control. I found an AAC control on Ebay. I have not located the Pump yet.

You must take the AAC apart to actually see if the circuit is burnt. Why are you spending money without actually knowing?

Once again thank you for the guidance! To answer your question...desperation! I removed the AAC controls again and found a #7 torx and opened it. Mine looks nothing like the picture, no damage at all...even using a magnifying glass. There are no traces burned or even discolored on the board, front or back. Do you still suspect this and the pump? I not replacing any more parts without sound guidance. Thank you!https://cimg7.ibsrv.net/gimg/www.mbw...a709536b4b.jpg

https://cimg8.ibsrv.net/gimg/www.mbw...26a3ef5b46.jpg

I have attached a couple of pictures. I'm new at this. I hope I didn't make a mess.

The board is fine. Reassemble it and reinstall, but just snap in the connectors. Then start the eng.and request A/C and wait a minute.

Then test RED wire, pin #2 for 12v, then test PINK wire, pin #1 for 12v. While the eng. is still running with A/C on turn blower dial all the way to #5. Then go to the firewall and feel both aluminum pipes. Are both warm or one is cold and the other hot?

As for the pump, turn the key to pos. #2 and test the WHITE wire for 12v. If there is 12v, then remove the connector until you get a new one.

One other question. When the mechanic evacuated and recharged the system, did he tell you if the refrig. was low and he had to add some?

My apologizes, I have probably made this confusing with too much detail...I personally replaced the compressor and (temp/pressure sw) because AC shop said it wasn't pumping, valves stuck open (85.00 for him to check). Took it back to him after changing and he evacuated and recharge at N/C, 27 oz of R134. Final reading were 125(H) 40-45(L). That was jumping straight to the unplugged compressor (which is hard to get to)and unplugging the temp/pressure sensor to get the radiator fan to run(which I discovered by accident). At these pressures it makes nice colds cabin air. Do these numbers sound ok to you? I looked for a site glass and AC shop nor I could find one like on other cars. The small line at the firewall was very warm (but you could hold your hand on it for a few seconds)and the large line was cold and making condensation after 10 mins running with the compressor jumped. Plugged everything back in and it did not work. He told me I would have to take it to MB Dealer.

I'm Very Sorry this is going on so long...Ran the test as you suggested. Plugged the AAC back in and left lying on the console. With the engine running RED wire 12v. PINK wire 3.1v. Unplugged and checked the coolant pump and the WHITE wire 12v. I left this unplugged as you suggested since I can not feel or hear it humming.

OK, it seems that everything is working correctly. So the only other possibility why the compressor is not getting the signal to turn on is that it is "Locked Out" due to a code being stored in the AAC Control Module.

You should find an independent mech. with a professional level scanner with Euro. package that can read and erase codes, or I strongly suggest you get your own scanner.

Thank you for everything! I have had it scanned at 2 different locations. I think one scan tool was a Marsteck or Mastek (2015 software update)and he was not sure he could see anything if it had a code but nothing showed that he could see. The other was a SNAP-ON (2016 software). He specialized in Euro cars VW/Audi and others but admitted MB was in a league of it's own. The latter gave me a report that I have misplaced at the moment. I believe there were 6-8 different levels that he was able to look in. In the heat/AC level there were no codes. All others clean too except Engine. Under the engine it showed a O2 sensor...left side I think. Once again, thank you for your expertise and help!

Any suggestions where to find/purchase a scan tool that would be suitable for this vehicle? I found it odd to have a O2 code stored and no check engine light.

This scanner will diagnose, read and clear all M/B codes in Trans., Eng., A/C, Air Bag, everything.

https://www.amazon.com/Autel-Maxidia...keywords=autel

Thank you again for your help and vast knowledge in this matter! This is a much better investment than to keep blindly buying parts!

Maj Dundee, I've been reading about this scan tool. Do you have one? Is it true that you must update the software each calendar year (one year free)or it does not work at all? at 100.00 each update? Do I understand that correctly?