98 ML320 ac compressor help - PeachParts Mercedes-Benz Forum

1994C220 · #1 05-23-2006, 10:48 PM

Hello everyone. After a long hard iowa winter, I went to turn my AC on and the compressor is not engaging. The blower operates, and the engine stumbles a little when you press the AC button, but no compressor activation.

To go back to last year....I have always had a problem getting my compressor to engage. I stopped worrying about it when it got cold. Now, I really need some help.

The compressor could be coaxed in the past(last summer) into activating after tapping( pounding lightly) on the fuse box.....I discovered this trick after a hot summer day of checking fuses with the engine on and AC running and slapping the fuse box in frustration.....anyway, so we made it through the rest of the summer slapping away at the fuse box....Now, I have no idea...

My question is, is it possible for the actual fuse box(the board that all the fuses and relays plug onto) go bad? I have lifted the fuse box and checked wires underneath to see if there was a short somewhere but everything looked good....I have priced the fuse box board at $150, but before I start throwing money at things, I wanted to know if anyone had any thoughts...

Thanks,

mbdoc · #2 05-24-2006, 08:14 AM

The A/C compressor signal travels THRU the fuse box...that signal is generated in the AAM (all activity module). Loose or BAD connection at that connector for the A/C compressor is COMMON/

1994C220 · #3 05-24-2006, 10:28 AM

That is good news, kind of....so that means I have the problem narrowed down to the fuse box...I just have a couple of questions....you mentioned the AAM, is that the big black thin box that mounts perpendicular to the fuse box board? Looks like the connectors for that are on the bottom. How would I check the connections?

I am getting ready to move back from Iowa to Houston, and that drive sure would be nicer with ac...

Thanks in advance.

mbdoc · #4 05-24-2006, 12:31 PM

The compressor wire goes thru connector "M/A" pin # 2, either a pink OR purple wire. look for bad connection...

The connectors are marked & plug into the BOTTOM of the fuse box..

ML320 · #5 05-29-2006, 01:58 PM

wire from M/A pin 2 in fusebox

sdanville · #6 06-04-2007, 11:14 AM

This is another thread with no conclusion.
Just wondering if you solved the problem.
I intend to pull the fuse box tonight...and look at my connections for my non working air.

mbdoc · #7 06-04-2007, 12:04 PM

Each of the connectors on the bottom of the fuse box are number OR lettered..

Connector " M/A " is the connection that goes to the compressor, PIN number 2 is the wire that goes there..either PINK or purple. check for overheating of the female pin.

sdanville · #8 06-04-2007, 01:09 PM

I will report back if anything works out.

1994C220 · #9 06-04-2007, 01:11 PM

The good news is that my AC is fixed, and has been fixed for a while now....it seems that this problem is either a loose or rusty connection at the AAM box under the relay box. I took the relay box apart figuring it had to be this AAM box and took it off the relay box(its attached to the underside of the relay box. I opened it up, took it completely apart and cleaned every contact point. I did notice that some of the connections were a little dirty. I put it all back together and voila!

I didnt have to buy a 500 dollar AAM module, and get it reprogrammed, and it cost me all of about 1.00 in cleaning supplies and q-tips for some of the harder to reach spots. If you are experienceing this problem, it is a good bet that the problem lies in a bad connection here...

Let me know if you have any questions.

sdanville · #10 06-04-2007, 01:19 PM

I have a few questions.
For starters...I should pull aout about 5 screws out of the top of the fuse box and all those wires and connections under the fuse box have enough play that I can pull it up a few inches then see and remove this connection ?
and maybe enough common sense will allow me to disassemble the gizmo.
I have Q tips and contact cleaner in stock.

I am printing out these pictures from above.

6/5/7 update. Took the Fuse box apart last night. Unplugged the connection shown in photo , it looked perfect. put it back together. Next I guess I will try and find this AAM part. Oh, and now I need a radio code. My documents and manual were stolen last week.

1994C220 · #11 06-04-2007, 01:19 PM

Make sure to take the AAM OFF the relay board!!! I did it the lazy way the first time and just cleaned all the relay plugs underneath(I took them off one at a time and cleaned them all) with no luck...it wasnt until I got daring and decided to take the AAM off the relay board(it wasnt easy) and cleaned those contacts that I fixed the problem. I broke one of the retaining clips on the AAM in my haste, but it is only a cover and I glued it back on...I dont forsee having to go in there hopefully ever again. I am in Houston now....and the AC is working great and has not quit on me since. I wish I could have found the problem before we drove down!!! I figured it out about a week after we got here.

I have since sold my 94 S320...I loved the car but hated the expense....and now have a Nissan Titan. So I have kind of jumped ship to the Nissan Titan forum... Wife plans on buying a new GL next year though, so I may be back on soon!!!! And of course this ML is pushing close to 160K....im sure something will give soon!

1994C220 · #12 06-04-2007, 01:25 PM

Yes, but disconnect your battery!!!!! there are some high voltage wires under there...

Yes there is enough spare wire so you can pull the entire relay box out...I think there are about 8 screws that hold the cover box and the relay box in...you need to take them all out...there is a warning on the box that warns of voltage, and thats why I did, of course on one of my cleaning ventures, I forgot to disconnect battery....I remembered after I had ac relay box out....

It is a good thing to check the ac before you put everything back....I left it out, hooked up the batt cable and turned the car on to check ac....of course that was before I ventured to removing the AAM box..

1994C220 · #13 06-04-2007, 01:27 PM

Its not that bad....getting the AAM is the hardest part....after you get it off, clean the connections on the AAM and where it hooks up to the relay board!!! thats what fixed it for me...i used flat tip screwdriver to scrape the contacts clean too....but do it gently.

1994C220 · #14 06-04-2007, 01:28 PM

I have to go....let me know how it goes