[RGCW1021]

2002 ML320 is only getting 3 volts to new AC compressor and should be getting 12 volt

Hi,

I just replaced the AC system in my 2002 ML320 and it blows very cold. The problem is my AC compressor is not getting enough power and I'm afraid it will seize up again. Currently it is only getting 3 volts and should be getting 12. Any suggestions on what the issue could be?

Thanks

 

[art_arev]

Hi, welcome to the forum.
Your compressor can't & won't operate on 3 volts. No device/equipment that is meant to work with 12v will operate on 3v.
Were did you get the idea of 3v? Maybe its 13?
What exactly have you replaced within the AC system & besides the erroneous 3v issue what are you not happy with?

 

[frustration_X_2]

I hate to beat a dead horse, or resurrect an old post, but...
I have a similar problem with a 1998 ML320.
Engine running.
Aux fans engage.
Interior blower running.
4.8V at the pressure sensor.
Static pressure on 134A system is 90PSI at 97F.

Alas, I've no voltage to compressor.

Anybody have another idea? ( Before I wire the compressor up to the fan relay! )

Not sure if it has any bearing, but the AC quit at the same time the water pump failed.
The AC quit before opening the hood to even look at the water pump, so it wasn't an ID10T induced failure. ( pronounced "eye-D-ten-T" )

 

[frustration_X_2]

UPDATE:
For curiosity's sake, I 'hot wired' the compressor to the fan relay. (Yeah, I know, but I did it anyway to test for functionality)

The compressor spins nicely. The pressures alter to just what I would think they should. (what they used to before this debacle.)

The problem is that it's still blowing hot air in the cabin!

No tick-tick-tick sound like the diverter motor is failing again, no fluctuation in temperature. Just nice hot air blowing from the vents regardless of the position of the HVAC controls.

How does THAT make sense?

The control module in the dashboard was replaced about a year ago. (with a junk one from Ebay) and it all looks ok.

I pulled it and opened the back panel to see if maybe it was fried... nope.
Put my ohmmeter on the soldier joints of the diverter controler... 3.7ohm in cool position, 1.0 in the heat position.

Any of your geniuses out there willing to help a dummy out of a hot zone?

 

[43sqd]

Static pressure means absolutely nothing when it comes to telling you how much refrigerant is in the system.

In other words you are probably low on refrigerant.

http://www.benzworld.org/forums/w16...rums/w163-m-class/2335153-ac-compressor-not-always-engaging-3.html#post12158521

Troubleshooting with Gauges FAQ

 

[frustration_X_2]

Update number 2:

After "hot wiring" the compressor, I had the system evacuated, vacuum tested, and recharged with 27 oz of R134A.

removing the "hot wire" returns the same results... Aux fans run, Interior blower runs, compressor clutch does not engage.


Ideas? Suggestions? Theories? <sympathetic comments welcome so long as they are accompanied by cash.>

 

[43sqd]

When you checked the voltage (which is correct) at the Refrig. Pressure Sensor, did you use the PINK wire as GROUND?

There is either one of two problems:

1. there is something wrong somewhere in the A/C system that is preventing the actuation of the compressor.

2. or there is an internal fault with the AAM which delivers 12v to the compressor via pin #28

 

[frustration_X_2]

Let me start by saying how much I appreciate all of your assistance.
I live in Texas, and if it weren't for my wife's car, I'd have to take this one to the $tealer-ship to get some cooling by now.

That said...This will be this weeks 'fun-time'.

I will pull that pressure sensor again and make sure I've connected my leads correctly.
Can I 'jump' the pressure sensor plug to see if the compressor clutch engages or am I going to blow something if I do?
(Again, it's just a test, not a permanent fix.... but it would tell me if the sensor is bad.)

The AAC on a '98 ML is under the fuses, correct? So I've got a bunch of plugs to pull apart if it's NOT the sensor. :-(

I love the 320 drive train. (mine and my wife's are both 320).
But the 'chrysler' part of this bucket is driving me insane... the squeaks, rattles, broken parts and such are driving me insane.

Thanks again!

 

[43sqd]

I will pull that pressure sensor again and make sure I've connected my leads correctly. Why do you have to pull the pressure to see if the connector is on properly?

Can I 'jump' the pressure sensor plug to see if the compressor clutch engages or am I going to blow something if I do? You cannot jump the sensor. Don't think about it.


The AAC on a '98 ML is under the fuses, correct? So I've got a bunch of plugs to pull apart if it's NOT the sensor. The AAM is under the fuse/relay module.

Remove both covers to the fuse/relay box. Then remove the three additional screws and pull the fuse/relay module out of the fuse box. Then turn it over and lay it on top of a folded towel.

Among the many connectors, locate connector X22, wire B4. One side of B4 will be a PINK wire and the other side will be BROWN/VIOLET.

Start the engine and then introduce 12v to either the PINK or BRN/VIOLET wires and see if the clutch engages. Only allow the compressor to run for 5 seconds and no longer.

The reason why your compressor does not engage is that you have a leak somewhere and there is no refrigerant in the system.

 

[Noodles]

I love the 320 drive train. (mine and my wife's are both 320).
But the 'chrysler' part of this bucket is driving me insane... the squeaks, rattles, broken parts and such are driving me insane.

Both the 98-99 MLs were designed and in production before Daimler and Chrysler got married. You can thank Johnson Controls for the noisy interior. They have a plant just down the road from MB's plant in Alabama to supply the interiors for MBs made in the US.

 

[gadha707]

As of MY 2002, the AAM is no longer a factor in turning on the compressor. That duty has now been assigned to the AAC Push Button Control Module. Your problem, assuming that you have a sufficient amount of refrigerant, is either the Pressure Sensor or the AAC Module or the compressor itself if everything is working properly.

Remove the connector from Pressure Sensor, key on. With a digital volt meter, neg. probe to brown wire and pos. probe to pink wire = 4.75 - 5.25 v.

Brn-neg Pink-voltage Grey-pressure signal Org-temp signal

Instead of jumping wires you should buy a new pressure sensor if you are getting the 5 volt reference, since they are not that expensive.

If all proves good, then you will have to take the AAC module apart and check for damage.

Hi,

I am new here, So hello to All.

my Dec 2002 ml320 had identical issue.

Are you able explain as to how to remove the connector from the pressure switch? Pictures would be awesome. I have tried and failed to find any obvious clip or click type mechanism which would release the lock (if at all). I don't want to force it too much not knowing the correct method.

Many many thanks.

 

[43sqd]

I haven't removed one in quite some time, but I believe you press the square area where the pink dot is and pull down. Remember to support the aluminum line while doing so.

 

[gadha707]

I haven't removed one in quite some time, but I believe you press the square area where the pink dot is and pull down. Remember to support the aluminum line while doing so.

Thanks mate. Will give this a try.

If found guilty, does replacing the pressure switch involve de-gas the system first, replace switch and then re-gas the system? Or can it be done while system remains gassed? Does the new switch have to be programmed in?

Have you used pelicanparts.com for purchasing parts? If not which site do you use?

Thanks again!

 

[43sqd]

gadha, this is not the problem. You are probably low on refrigerant.

You should always state what your problem is instead of self diagnosing it. Just tell a short story.

 

[43sqd]

You state that you have an ML built in Dec. 2002, so that makes it a 2003 ML.

Please UPDATE YOUR PROFILE in USER CP.

 

[gadha707]

gadha, this is not the problem. You are probably low on refrigerant.

You should always state what your problem is instead of self diagnosing it. Just tell a short story.

The story:

The air conditioning stopped blowing cold air. Took it to mechanic A, he said refrigerant level is fine, but the clutchless compressor had sticky valves inside and offered to service it (or perhaps replace those valve components internal to the compressor unit).

Took it to mechanic B (air-conditioning specialist) to get a second opinion. he hooked up pressure gauges and I have witnessed the pressure on both high and low is around 85 psi regardless of AC being requested or not. He used his scanner and was able to read real time values of 7 bars pressure and 215 temperature. The readings were somewhat static as he said. he also said that 215 might just be an integer representing some temperature values (not necessarily a direct F or C value). He scanned for trouble codes and i believe he got B1231 which he checked with MB over the phone and narrowed it down to the temperature/pressure sensor (as you have shown in the diagram). Also, he tried to force start the compressor from his handheld and failed to do so.

Comments:
I have checked all fuses and none blown.

The AAC control buttons/dials seem to perform all the supporting functions such as, adjust blower fan speed/direction based on set temperature etc.

However, leading up to the air-conditioning failure, cooling was not the strongest.

 

[43sqd]

Static pressure can only tell you that there is some refrigerant in the system, but cannot tell you if there is enough or the required amount.

Troubleshooting with Gauges FAQ

There is no Merc. A/C code B1231.

The first thing to check is fuse #5 in the right side kick panel fuse box. If it is not blown.................

Remove the radio with required keys, then remove the Center Section of the I.P.

Disconnect the four electrical connectors to the AAC Control Module and detach the AAC Module from the Center Section.

Then remove the seven tiny screws with a T7x40 screwdriver and remove back cover.

Check to see if the circuit is burnt.

 

[gadha707]

Static pressure can only tell you that there is some refrigerant in the system, but cannot tell you if there is enough or the required amount.

Troubleshooting with Gauges FAQ

There is no Merc. A/C code B1231.

The first thing to check is fuse #5 in the right side kick panel fuse box. If it is not blown.................

Remove the radio with required keys, then remove the Center Section of the I.P.

Disconnect the four electrical connectors to the AAC Control Module and detach the AAC Module from the Center Section.

Then remove the seven tiny screws with a T7x40 screwdriver and remove back cover.

Check to see if the circuit is burnt.

Hi mate,

Thanks for the instructions and sharing your knowledge. And apologies for the delayed response. I have been busy and didn't get a chance to work on my truck.

I was able to pull out the pressure switch connector. The below are observed:
1. With the connector removed, the cooling fans come and stay on at all time while the engine is running (whether or not the AC is requested).
2. With key out, key in, key in ignition position or engine running (at the connector): voltage between Brown and Pink is ~5V.
3. Interestingly enough, voltage between Brown and Grey is ~5V; voltage between Brown and Orange is ~5V. [I was expecting these voltages would be near 0 while the connector is pulled out. (With an anticipation that) while the connector is in, the pressure and temperature sensors will work like variable resistors (ranging between mega-ohm to micro-ohm) and thus will introduce voltages ranging from 0v to 5v to the Grey and the Orange.]

If I must jump wires (to mimic a pressure and temperature value temporarily), how do I achieve that? Wanting to ensure that the compressor kicks in. Assuming pressure is sufficient (assuming 85 psi on both high and low side is sufficient to tell the compressor to start), this test should tell me if the sensor or the compressor is at fault.

 

[gadha707]

I have read the article on refrigerant pressure and the use of gauges u quoted. From there, 85 psi reading appears to be not too low. So at this pressure, the compressor should kick in (at least to start with.... it might later cut out due to insufficient refrigerant).

Based on the above, I am assuming that there is at least sufficient refrigerant to begin the process.

 

[gadha707]

And Fuse 5 is not blown. All fuses are intact.