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2002 ML320 a/c not working need help

7K views 26 replies 7 participants last post by  B&kML350 
#1 ·
Hi,

I have a 2002 ML320 that the A/C was working and now it just blows regular outside air. It started acting up where the a/c would stop blowing cold so i would have to turn car off then back on and it start to work again. Now it does not blow cold at all. I thought i had a leak so i went to add freon but when i put the gauges on it read 90psi on both High and Low side. The pressure would not change when i turn on the a/c. So i read the forum and read how to see if i was getting power to the Pressure Sensor. It reads 4-5 volts which i believe is fine. What's wierd is that as soon as i disconnect the sensor the fans kick on but still a/c pressure stays the same. I also tested voltage on both the sensor in the back of the compressor and on the single green wire (is this the clutch power wire? cause i thought this was a clutchless system). both read from 1.5 - 4.5 volts. I also took apart the a/c heater control switches and didn't fine any burnt spots or anything wrong. i even wiggles the wires while having the a/c on high without any change. Can some one help me figure out what is wrong? Thank you so much for any help.

1. How do i test if the compressor works if it is a clutchless system, can i supply 12v to that green wire or will this burn the compressor.
2. how do i test if it is a bad pressure switch
3. how do i test if it is a bad a/c switches in the cabin.

I live in the Orlando Florida area if anyone has a similar ML320 for me to test it with. Thanks so much.
 

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#2 ·
Update:
I tested the voltage at the green wire going to compressor and the black and red wires goign to the back of the compressor and both read 4.93 volts. Does this mean that the compressor is bad or that there is not enough voltage to the compressor?
 
#4 · (Edited)
The first thing you must understand is that reading static pressure (without the eng. running) does not guarantee that there is sufficient refrigerant in the system. Please read static pressure section.

The second thing you should know is that if there is insufficient refrig., the system goes into protection mode and the compressor will not operate.

Once you disconnect the Pressure Sensor, the AAC control Module thinks that something is wrong with the A/C and turns the fans on.

First check fuse #5 in the right side kick panel fuse box to see that it is not blown. Then remove the AAC again and see if you are receiving 12v at the RED wire connector A, pin #2 .

Then make sure that the very tiny connector D is secure at the back of the AAC. Also make sure that the white corrugated tube is attached to the back of the Low Range Switch.

If there is no problem with any of the above, then in all probability you are low on refrig. and to get things right you will have to visit an A/C professional to check for leaks and recharge the system.
 

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#6 ·
Ok so replaced the fuse #5 on the kick panel just in case because the old one was fine. I also tested to see if i was getting 12v to pin #2 and i got 12v with car off and 14v with car running. Anything else i can test?

1. How would i test if the pressure switch is ok
2. how do i test if the compressor clutch is working


thanks so much 43sqd
 
#12 ·
1. How would i test if the pressure switch is ok I do not have a test for the 4 wire Refrig. Pressure Sensor. The only thing you can do is remove the connector at the sensor, turn the ignition on and with a DVOM check for 4.75-5.25V between the PINK and TAN wires.


2. how do i test if the compressor clutch is working
a. remove both covers to the fuse relay module.

b. then remove the three additional screw to the fuse/relay module. Pull the module up and out of the fuse box and turn it over and lay it on top of a folded towel.

c. locate connector MR/E pin #7 PINK.

d. start the truck and turn the A/C switch on.

e. use a jumper wire (same size as PINK wire) stripped at both ends. Connect one end to the back end of the PINK wire and the other to the 12v battery stud indicated.

f. if the compressor and clutch are not faulty the compressor will turn on. DISCONNECT THE WIRE once it has turned on.
 

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#13 ·
43sqd,

I went ahead and connected a wire from the pink pin #7 to the power and the compressor started to work. I had my wife inside the car while i held the wire and she said it got ice cold. So the compressor works fine. hurray!!!!

I also tested the AAC and i am receiving 12v at the RED wire connector A, pin #2 . Does this mean that it is fine or just says that it is getting power. Any way to jump power from the AAC to turn on the compressor? Just in case, the unit seems to be working fine where all the knobs turn and light up according the the position. The auto also turns on and the AC off button also lights up. Any other test i can do on it?

Any way to test the Pressure Switch or jump it to see if it is bad?

43sqd Thank you so much for all the help you are giving me i do appreciate it.
 
#17 · (Edited)
Start the truck and with your hand, feel to see that the Coolant circulation Pump is working.

Do you have a scanner or code reader? Be specific as to make and model.

Understand that the AAC is a small computer unto itself and stores its own codes and they will be stored in the ECM. So it is imperative that you check for codes. And if there are codes, the AAC will not allow the compressor to turn on.

Did you personally add refrigerant to the system?

Briefly explain how this problem occurred. Did the A/C work one day and not the next?
 

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#18 ·
So i went to test the Coolant circulation Pump and couldn't tell if it was running so i tested for 12v at the connector to the pump and it had voltage. So then i noticed that at the bottom of the pump the little nipple was not spinning so i started to tap the case lightly until the motor started working. I then let it run for a few minutes the restarted the truck and the pump was working again. so i then removed the positive terminal from the battery to see if i can reset the system. after 3 min i plug the battery back in and tested the ac but it did not get cold. The pump was still working.

The a/c was working fine but it started to stop getting cold so i would turn truck off the back on and system will get cold again. This happened for about a week until one day it stopped working all together. I don't have a scanner but i can go to Advance Auto Parts and they can do it but i don't think it will read other codes besides the regular car ones.
 
#20 ·
So i was in a crazy mood today. I went ahead and connected a wire to the connector MR/E pin #7 PINK and a fuse (just in case) to the red post to make the compressor run. I left it on for about 8 minutes to see how cold it would get. While doing this i noticed that the auxiliary fans in front of the radiator kicked on for a minute or two then back off. So i am thinking that this shows that the Pressure/Temp sensor is working correctly. Am i right?

If this means that the Pressure Sensor is working then that only leaves the AAC right? How would i test it to see if it is sending the right signal to turn the compresor on? I was also going to take it out and resolder all the joints just in case. This is what i had to do on my old Porsche 944's computer.
 
#22 ·
Art_arev,

Thank you for all your help. I will try to solder every point i can tomorrow. I don't know of anyone that has a 2002+ ML320 in my area, Orlando, Florida. I also have not been able to find a 2002+ ML320 at my area junk yards, most of them are 98-2001.

:-(
 
#23 ·
It doesn't have to be a 320. Any 2002-2005 ML will do. Be extremely careful. There are so many micro electronic parts in the AAC........Its soldering hell........If you can find a second hand one from a junkyard(any2002+ ML)at a good price, buy it. You will need a spare, at one time or another. I would, instead of trying to solder micro electronics. I hope you have a hot air solder......
 
#24 · (Edited)
freek, the initial jumping of the PINK wire was only a test to see if the compressor was operational, not to run it for an extended period of time. Doing this could damage your compressor or any other part in the A/C system.

Even purchasing a used AAC module might not correct the problem because there are codes stored in the ECM and the compressor will still not operate. What you are doing is ignoring the info that I have supplied.

If you still want to buy a used control module, fill in the blanks to this link and you will see that there are many in your area.

Car-Part.com--Used Auto Parts Market
 

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#25 · (Edited)
Before buying one or trying to resolder yours, remember 43sqd's statement:
Understand that the AAC is a small computer unto itself and stores its own codes and they will be stored in the ECM. So it is imperative that you check for codes. And if there are codes, the AAC will not allow the compressor to turn on.

Don't ignore this!!! This is vey important. At times we get so eager to "fix", we forget important points.......
 
#27 ·
43sqd No not yet I have studied every part of the A/C circuit and have a pretty good understanding of it's function. I have just purchased an Autel Maxidiag elite 802 so that I can read the codes myself. When it gets a little warmer I will be back at it.

I will post everything once I get this fixed.

Also thanks Art for the connector info
 
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