I'm not sure if I wore out my welcome or have just wore out the folks on another forum so I will try here.

I have a 98 ML320, W163.
Brief history:
A/C blowing hot air so I rigged the blend motor flapper to be in cool mode only because it was clicking. Worked good for quite some time.
Wife comes home saying the A/C is not working and blowing hot air. I figured the rig had failed.
Pulled the dash, replaced the blend motor. Checked the actuation by working the the temp control selector on the A/C control panel. Worked as expected but still no cold air.
Checked for clutch engagement and it was not working.
Checked the system refrigerant pressure and OK, over 3 bar according to scan tool and pressure gauge.
Jumpered the clutch to 12V from battery, no engagement.
Checked continuity of clutch - open circuit.
Checked signal to clutch from controller (AAM X22). No output (12V)
Ran test procedure for N19 (see attached)

Here is where it gets interesting
Connected scanner and checked AMM status, this is what I found:

AAM - No codes found

AAM Status:1. Ac comp status off. - Agree
2. Ac comp shut off because of high engine load. status on.
3. Ac request from n19 recognized. - A good thing. But when I run another test, N19-9 to N19-4, ignition ON, A/C button illuminated and blower at stage 4, I do not get >3 VDC
4. Ambient temperature 87.5 c. - What? That is 189.5 F. Could this be a failed sensor or sensor input?
5. Battery voltage 11.7 - Agree as I have been running the interior blower.
6. Emergency off circuit of ac comp is on.
7. Engine temperature 26 c - This temp looks correct.
8. F1k19 circ. pump relay off - Not sure what the status should be.
9. F1k21 blower motor relay off - This one puzzles me as the Interior blower motor is working fine in all stages.
10. F1k26 engine fan stage 1 relay on. - Not sure what the status should be but I do know if X22 is disconnected, both fans run.
11. Refrig pressure 3 bar - I realize this is pretty low but the specs call for >2.75 bar <??
12. Switch on request to interior blower from stationary heater off - Not sure what the status should be.

Have I been locked out?

I'd like to get to the root of items 2 and 6. With item 4 being so far out of wack, could that be contributing to the issue?

How does one get rid of items 2 and 6 if it is the responsibility of the AAM and the AAM shows no codes found? If the error codes are driven by the HVAC control panel, how do you reset that module?

From what I have read and understand is that a "flag" has been set thus disabling the output signal to the compressor. Is this "flag" something that can be eliminated by simply disconnecting the battery, let it sit for a while and then short the plus and minus leads going to the vehicle, let it set for a while, maybe?

Now, really reaching here, is there a coil sensing circuit for the clutch that determines the health of the coil? We do this in the nuclear industry. If the readings are out of spec the circuit flags an error.

All feedback is appreciated.

regards
- rev -

 

Try replacing N19.

https://www.ebay.com/sch/i.html?_fro...-0471&_sacat=0

 

Over 3 bar, what does that mean? 3 bar isn't enough neither is 4 bar; that will trigger low pressure cutoff. Connect A/C gauges, you should have 80-100 psi with the engine off. Basics first, go down the rabbit hole later.

 

You are referring to the high side I take it. What should I see on the low side? The only gauge I have is the cheap one that comes with the can of refrigerant.

 

Both sides will be the same with the engine not running. If you have just run the engine, it will take a few minutes after shutting off for both sides to equalize.

 

I kinda figured that. The best I can get is ~5-5.5 bar out of one of those refrigerant cans and that puts the gauge well into the red. Still no output from the AAM.

 

Hello again folks -

I've read error codes and status with a different scanner (i980). Here are the results of the AAM:
All readings are with ignition on/engine off

Fault codes:
B1040-000
B1040-001
From what I understand these are start codes but the vehicle starts just fine.
I've also read that these could be "ghost codes".

Digging into AAM A/C view data status:

Compressor - Off
Compressor shut off due to High engine load - On <--- This one bugs me
Request from N19 - Recognized when A/C button pressed off when not pressed.
Ambient Temp. - 87.5 C <--- This one bugs me too
Battery Voltage - 12.08 V
Emergency off circuit -
On with blower motor off and ac select off
Off with blower motor on and ac select on
Engine Temp - 23 C
F1k19 recirc pump relay - Off
F1k21 blower motor relay - Off (Although the blower motor runs in all stages)
F1k26 engine fan stage relay - On
Refrigeration pressure - 5 Bar

All insight on this matter is welcome.

Thanks again.

 

I was the first responder and suggested you replace N19 and you completely ignored it.

 

Well, Mr. Maj. I did not totally ignore you. I pulled the unit, did a through visual inspection and tested it down to the component level and found no issues. After your second comment I thought “”F” it, I’ll try another module. After repeating the same test procedure for N19 (given to me by someone in this lengthily thread) on this other module, my compared results are represented in the attached document. From the data shown, It looks like I wasted money on the purchase of the N19 module but my time was not wasted as the data indicates that the N19 module can be ruled out as to be the issue. I will not further investigate this newer module as it has a tamper proof seal indicating that it has been tested to be OK.

I also ran the i890 scanner with the newer N19 module installed and the results were identical.

So, this leads back to the “how does one reset the ‘ A/C compressor shutoff due to high engine load’ “ question. This status is “ON" with the ignition in the on position but the status is “OFF" with the key removed.

Possibly, if someone (Witek) has a scanner to monitor this status while the ignition is on and off they can report back their results.

As much as I hate to, I’m about ready to tear into the AAM and look for obvious issues.

Again all, thank you for your time and patients.

Pleasantly pissed.
Jm. B. Jones

 

Sorry about N19.

Witek is only available on this forum.

https://www.benzworld.org/forums/w163-m-class.35/

 

In this video ( ) they call out a fuse panel located in the passenger side foot well, behind the kick panel. This is for 1998 - 2005 models they claim. I do not find one there. Is it not part of a 98 model or is it located elsewhere in a 98 model. The only fuse panel I find is under the hood on the driver side.

Please advise

 

Rev, the kick panel fuse box was added in 2000, so you do not have one.

What are you looking for?

 

I'm looking for anything that may shed some light on why this compressor is locked out.

 

See if this helps.

 

aa

 

Thank you for the feedback. I have already looked into that and the sensor signal appears to be functioning properly. At one point I read that the minimum system pressure was 2.75 bar although on this system the A/C compressor enable signal is on at ~5 bar and is disabled at ~4.5 bar. All of that looks OK. The issue I cannot seem to get passed is the "A/C compressor disabled due to high engine load".

 

Are you sure that the system has enough refrigerant?

 

Yes. As I say, I can discharge the system to ~4.5 bar and the compressor enable signal is lost and if charged to >5 bar the compressor enable signal is on. But all the while, the "A/C compressor disabled due to high engine load" is on.

 

What is the code # for this and what module was it in? Ac comp shut off because of high engine load. status on.

 

In the Icarsoft i980 this is a status condition listed under diagnostics reading the AAM under the Air Conditioner menu selection. It gives you info on things like compressor state (on/off), compressor safety circuit (on/off due to refrigerant level), request for A/C from N19 (off/recognized), ambient temperature, etc. including A/C compressor disabled due to high engine load (on/off). And BTW, it is "hight engine load" but I'm sure that is an overlooked mfg defect. There are no codes in the AAM itself.

 

I have refrained from being rude and crude throughout these threads. But, I’m pretty ****ed up about my latest findings. I ensured that the battery was up to snuff (which it has always been) and decided to connect the newly purchased clutch to the skinned wire going to the existing clutch on the compressor (which is an open circuit). I started the truck, turned on the blower and pushed the request for A/C button then measured the signal to the clutch. 12.5V. I put a non magnetized ferrous screw driver on the clutch and found there was magnetism.
Now, as reported earlier, the refrigerant pressure was 4.5 bars according to my scan tool and the scan tool status said that the "A/C emergency circuit off" was in the “ON" state thus disabling the compressor clutch from turning on or does it mean the circuit is ON allowing the circuit to pass the signal. As well, the compressor off due to high engine load. I either don’t trust this ****ing scanner or do not know how to interpret the data. Bottom line, original N19 installed, blower motor on, A/C request pushbutton on and clutch signal 12.5V. WTF with all these erroneous status indicators from this i980 scanner?

Regards
Really pissed now. Even though things work.
I just want to understand it. As I asked before, is there a sensing circuit that detects if the clutch is there or not?

 

I have to be frank, your posts are extremely long and hard to decipher.

Here is what I have relating to the AC Lockout and the clutch and after this I am done with this thread.

 

Really. What exactly did you not understand?