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2001 ML320
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3 Posts
Discussion Starter #1
OK first I am new here and I have to say THANKS...I got an ML320 - which I like - last Friday and I did see some obvious things to fix but they neglected to tell me that the AC wasn't working (nice, huh? They knew it was for my 17 year old daughter - who does that? Oh well the ol girl is in good hands now...)...so I got on to Google and started trying to see what to do to fix everything...SO you have all helped me: fix the glove box that was pulling out on the left side, fix the machine gun lock, fix the power windows, troubleshoot AC issues to save untold hundreds in labor...given me wiring diagrams galor to check the relays, THIS PLACE IS GREAT THANK YOU!!!

2001 White ML320 203K miles
Engine sounds good, regulates its own temp

HERES WHAT I HAVE ALREADY DONE IN TROUBLESHOOTING:

**I turned on the AC, light illuminates on button, air blows but no cold air.
My daughter and I did seem to feel a spit of cold air once (imagination? Hopeful thinking in the 106 degree heat wave??) :(

**I had it evacuated and recharged, still nothing. :(

**The AC mechanic said the compressor clutch is not getting the signal to start or is not starting the compressor but that the compressor wasnt locked. He said the equipment in the system all seems to be working ok, that they thought it was electrical in that the clutch seemed ok it just wasnt being told to turn on.
So from studying the forums I gather this could be
A) the in car temp sensor located behind to the left of the radio behind the wood panel under the low range switch OR
B) the hi/low pressure switch (B12)? Or
C) the wiring between those things to the compressor?
Getting codes Tuesday AM unless someone can post instructions on pulling AC error codes using a button sequence?

**I asked them to check the air blend motor/actuator. They said it was ok, and I did recheck and when you turn from hot to cold and back you hear a very very quiet sound like its moving, sounds good to me, (but ...maybe its my imagination it seems to slowly get hotter, but maybe thats engine heat).

**Checked for the fuse 44 repair and it was done, replaced 44 fuse although it didnt appear fully blown it could have been, but regardless it still didnt kick on after fuse replacement. Checked all the fuses and relays, all were good. Went to MB Rocklin to verify I had the right part number relays for my ML and he came out and looked at my relays and said they were ok. (For FREE! Wowza)

QUESTION ONE:
In car temperature sensor does appear dirty in the grill with dustbunnies/lint...I still have the glove box out, should I take out the radio and get to the sensor, clean it and check the connections? I assume if I take out the radio I can get to it (again thanks to these blogs I know that...) cost for new one is 124 at MB Rocklin - ill search for shortcuts on how to do this...

QUESTION TWO
Havent taken off the hi/low pressure switch to clean it yet - it that safe? Im not sure why but that scares me...will it affect the charge? Cost for new is 184 at MB Rocklin - any tips on that? What the easist way to access it? I have the diagram but theres that body panel above it...

QUESTION THREE - I AM SO CURIOUS TO KNOW:
CAN I PULL THE AC ERROR CODES THROUGH A BUTTON SEQUENCE ????
I dont have a "REST" button (theres no button that actually SAYS that, my R350 SAYS it on the button) so I am lost as to how to sequence or check the AC error codes :(( please let me know!!!!

Also just putting this out there in case anyone has these:
Still need:
*the three gray headrests for the rear seat
*third seat
*new rear exterior pillar facias - both sides (not sure of the exact name) (both are cracked about four inches up from bottom I am trying to figure that one out...)
*RR tail light cover
*front bumper (white) (current one has minor crack on left side)

OK sorry for the long message
Thanks!!
Nancy
 

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Registered
87' 190E 16V / 93' 600SL / 02' G500
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1,197 Posts
Does the system have freon in it? Compressor will not engage if the system does not have sufficient freon in it.
 

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Registered
2001 ML320
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3 Posts
Discussion Starter #3 (Edited)
Hi!

Yes I had it recharged first, and filled with R134 -

This morning I looked at the hi/low pressure switch (B12) and also noticed that the radiator had the TINIEST slightest leak at the point where the hose enters radiator, right next to/above the low pressure switch. I wonder if this maybe shorted the switch out? There isnt any obvious corrosion on the switch but I havent removed it completely, its hard to get to. Im going to try liquid weld for the radiator thing since it is at the connection.

I noted that when I press recirculate, the air doesnt blow harder, at least it isnt noticeable. I also gently cleaned the area around the interior temp sensor and jiggled some of the wires around with the AC running but - nothing :( I did also unplug/replug and look at the connections on the hi/low pressure switch and it seemed ok (not blown)...its a 185 part new sooooo not really excited about replacing thatttt...if its out will it show on the codes??

I have read about people jumping the power from the switch to the compressor but I am not quite sure how to do that, havent found a specific thread yet...I guess that would prove it, right?

I dont have the tool for the radio, im trying to find a way to do that without the tool now (searching old blogs :)) - I do have that appt Tuesday to get codes - when it cools off later today I am going to try some ohm readings :)

This sure has been educational! Also learned this morning:
removal and replacement of headlight/taillights & bulbs

Credit again goes to these forums! :thumbsup:
 

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Registered
87' 190E 16V / 93' 600SL / 02' G500
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1,197 Posts
To test the compressor just disconnect the pressure switch and bridge the connectors for a few seconds. This will test the system hooking power to the compressor will just test the compressor. My guess is there is not enough pressure in the system to actuate the compressor. That said get on repairing that leak before getting too excited about looking else were for A/C issues.
 

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Registered
2001 ML320
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3 Posts
Discussion Starter #6
ME TOO! But the locks seem to be isolated to the one left rear, and it did improve slightly (went to a one-shot from a machine gun) so I am thinking its the one...hoping...I am mentally prepared if it is the AAM...The other locks do lock, and there are no wiper problems or the others listed...

It does have full R134 freon/refidgerant from the AC place from a few days ago. They said there weren't any leaks they could see (it was there 6 hours).

Does the pressure switch twist or pull off?
 

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Premium Member
02 ML320 06 ML500
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17,104 Posts
To test the compressor just disconnect the pressure switch and bridge the connectors for a few seconds. This will test the system hooking power to the compressor will just test the compressor. My guess is there is not enough pressure in the system to actuate the compressor. That said get on repairing that leak before getting too excited about looking else were for A/C issues.
Mike, this switch is totally different than the 2 wire Pressure Cycling Sw. found on older cars, which were not computer controlled. The newer ones, 3 wire, are AAM controlled, and if any two wires are jumped it will toast the AAM.
 

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Premium Member
02 ML320 06 ML500
Joined
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17,104 Posts
Assuming that the evacuation and recharge was done properly and the Blend Door Motor sounds like it is operating properly, you have a signal problem to the compressor.

First remove the panel (with plastic pry tools) surrounding the radio (radio removal is not necessary) and check that the Low Range Switch and its wiring is in place and not broken. Also check to see that the sampling hose is in place.

Test the Refrig. Pressure Sensor wiring with a volt meter. Neg. to Pink and Pos. to Tan. DO NOT JUMP ANY WIRES.


The remove both covers from the fuse box and then one or two additional screws and pull up the fuse/relay module. Locate the X22 connector and go to the #9 wire. One side will have a Pink wire and the other side will have a Brn/Violet wire.


With eng. off and key in hand, separate the connector. Fashion a length of 18 gauge wire stripped at both ends. Attach one end to the positive battery post and with the other end momentarily touch the pin to the Brn/Violet wire. You should hear a "clack" sound signaling that the compressor clutch has engaged. As soon as you hear the "clack" remove the wire.

There is no button sequence on the ML as there is on other models. Codes can only be extracted using a professional scanner or the MB SDS.
 

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