Gents,

I want to share some...........

I told my indie, if there is an MB of a friend of mine, direct or indirect and has trouble, call me. I will fix it...for practice sake.
The day came on late May 30th and I was still in Bali and would be back to Jakarta home base only on 31st.
1st - 4th June was holiday in Indonesia.

Issue was :
01. Fan speed maximum at all times. <<< This is the main reason owner sent car to my Indie workshop.
02. AC is cold only when engine is still cool, when engine already warmed up, AC no more cold.
NO DTC at all


1st June I got itchy and I told him to open up workshop for fast troubleshooting, I want to see the car.
If issue is not found out, I want him to send the car to my home so I can take my own sweet time.

So there I was, 1st June troubleshooting this Code 581 air conditioner on a 2011 AMG CLS63, 5.5L M157.981. W218.374
My W212.065 E400 is code 580 AIR-COND, lower grade one.




I look at the Xentry for N22/7 AAC module for refrigerant pressure reading while car engine OFF and all components are ambient temperature.
I hook up my wireless Fieldpiece JL3PR pressure gauge to both LP and HP port.

I saw N22/7 AAC refrigerant pressure at 29.5BAR or 427 PSI !!!!! Dugghhh, no way Jose.
My own digital pressure gauge was showing LP at approx 80 PS and HP at 135PSI.
Ambient temperature was 32-33C / 89.6 - 91.4F ..... Hhhhmmm, the N22/7 AAC refrigerant pressure at 29.5BAR is no surprise, that is 100% guaranteed a pressure sensor which already drifted way too much.
My own digital pressure gauge reading, the HP one is what worries me, that 135PSI value. At this temperature, 110PSI is the highest R134A can be.




I then requested engine ON and then 30 seconds later, turn on the AC system.
LP was showing no lower than 75PSI or so and HP side like 150 PSI or so, I forgot the exact numbers but I know the compressor was at 300ish Ma or equal to 30% duty cycle.
This is not right, LP is too high and 300ish milliamps is not the duty cycle to see, first time aircond running would be 950Ma or 95 to 100% duty cycle.
Fan was running maximum speed and aircond was not blowing cold air.

At 75 PSI LP side, that R134A temperature would be 22.8C or 73F.

I requested engine to be turned OFF.
I then bleed out the R134A from LP side, to get the HP side reading to be 110 PSI and it did came down to 110PSI.

I then requested engine and aircond to run again.
This time LP side goes down to like 42 - 45PSI there about, the HP side I forgot what is the value, but never higher than 175PSI.
The compressor duty was still like 380 Ma approx.
The blower started to blow slight cooler air and the EVAP temperature decrease too, down to 13-14C / 55-57F.

At 42-45 PSI, R134A temperature would be 8.3C to 10C or 47 to 50F.

I stop the test there then and I told my Indie, I will continue on 5th June ( today). I so happened to have the refrigerant pressure sensor on hand at home, as I wanted to replace mine for preventive measure being a 9 years old unit/car.


==================================

Over the weekend I was puzzled by the excess 25PSI of HP side pressure, does not make sense. Should be 110PSI but I get 135PSI at that temperature.
It can be 135PSI at that temperature, if the car R134A is not pure and have some mix of R22.

R22 has higher saturated temperature if at the same 32-33C / 89.6 - 91.4F , approx 170 PSI.




But then , its hard to confirm anything without a true refrigerant analyzer, which I will never buy....too expensive , cheaper to dump out all the refrigerant from the car and charge it with a known genuine R134A.

=========================


Today I visited the car again, but I did not recover the R134A like I usually would , so that I can measure the charge weight.
I dump slowly for approx 20 minutes the refrigerant from LP side. Sorry Gents, there is no recycle service for automotive refrigerant in my country and no law governing it too.

The refrigerant pressure sensor has a positive drift value of 285 PSI, damn !!!




If connector to refrigerant pressure sensor disconnected, there will be DTC and the value will shoot as seen below :


That 65,*** value seems to be a common PID formula in OBD.
https://en.wikipedia.org/wiki/65,535


CLS63 has a VERY EASY location for its refrigerant pressure sensor, unlike my W212
It is under the condenser, lots of real estate to work with, unlike mine at the side ( LEFT ) of the condenser and lots of stuff got in the way.









Testing new refrigerant pressure sensor with nitrogen.




Pressure test with nitrogen to 120PSI for 10 minutes All good, no leak.

Took the whole load of my HVAC gear, bring it over to my Indie



R134A Fill weight for this car, code 581.




Vacuum for 2 hours. Purge with nitrogen 3 times. Each 30 minutes a part.



Charge R134A to 645 grams including purging , so I am dead accurate to 640 grams, error rate max +-5 grams.....yipeee !!!
460 grams in liquid form and then the rest in gas form and the left over at the hose was only gas form. If liquid form, my 120cm hose will hold approx 35-40 grams of R134A


.
Now the moment of truth. Will fan kick maximum speed when AC turned ON ?




Fan no more maximum speed. Nice.




So why did the fan went full speed before refrigerant pressure sensor replacement ?
Because AC computer was "calculating" that the R134A at the condenser was too hot at approx 88C or 190F...based on erroneous value of 29.5 BAR or 427 PSI.





Here I find that MB engineers programming is a dumb-azz one.
Other cars have what they call rationality check DTC.

What they should do is, when engine coolant temperature is the same as ambient and add 12 hour count down since engine last turned OFF as insurance, meaning engine has cooled down back to ambient temp,
there then the refrigerant pressure uses the R134A pressure-temperature chart to define pressure sensor value make sense or not ? Allow error rate of +30 PSI is okey too.

So example at 35C or 95F coolant and ambient temperature and 12 hours engine been OFF, the R134A pressure will never exceed 114 PSI. Thus the ceiling of +30 PSI is 144PSI ( 43C / 109F ) , higher than this AC computer is to issue
Refrigerant Pressure Rationality check DTC for owner/workshop to start troubleshooting.


==================


Aircond performance not bad..................... 3 Minutes 45 seconds compressor is running. Fan stay nice and slow-medium, no more jet engine sound... LOL.










WILL CONTINUE...................

 

I am pissed that I did not have historical information on this CLS63 aircond works since day 1.
It came to my Indie for the maximum fan speed issue and not for aircond works. My indie does not do aircond works.

I am seeing there is a possibility that this car has one point in time uses service from a RRR or 3R aircond service machine which is able to re-inject new compressor oil when some oil get taken out during recovery.
Any 3R machine operator who likes recovery from HP port , will suck out compressor oil .

I am seeing what seems to be universal compressor oil NOT MIXING WELL with the Denso ND8 oil our Denso compressor is using.
Universal oil is a big taboo.


See the un-even mix.

Nissen 101 on the so called Universal Compressor Oil https://www.partinfo.co.uk/files/Nis...O%20mixing.pdf



This car only done under 15,000KM, although a 2011 car or 12 years old.
It seems the oil aging becoming brown color is also a time based one and not distance based alone. This is more brown than my car if not the same browny , mine with 37,000KM but 9 years old.
Well, M157 has more power and the engine bay is so crowded, everything inside that engine bay would suffer heat stroke...LOL





My car, below : Image can't be as good as the CLS63 one, I was doing vapor suction, so the liquid R134A is not motion-less like the CLS63 photos.





Comparing pure Denso ND8 pure compressor oil on my E400

 

@S-Prihadi thank you so much for this thread and your research!! as I think I have the same exact situation on my 2015 E. 63S which has the air-conditioning cutting off when the cars been sitting outside in the hot sun, then the fan goes at maximum and won’t stop.

When the car has been in the garage and the air conditioning seems to work fine is normal

Was the air conditioning pressure sensor the only thing that you changed to fix?

I am hoping to avoid evacuating and recharging the entire system just to replace that sensor, but if I can replace the sensor myself, that would be great. Thank you so much.

 

Nope, no way you can avoid evacuation and recharging, when and if anything of the refrigerant pressure system get opened up.
In fact if you do not do like I did with constant nitrogen pressure, 5 psi is enough.....while removing and install new refrigerant sensor, your filter drier will go bad.

The only work on AC system in our car, where you get away from NOT having to renew the filter drier is that refrigerant pressure sensor replacement, because the sensor hole/port is small and we can keep
having dry nitrogen leaking out of it at 5 psi while we replace the sensor. So no ambient air ever enter the AC system.

While AC system looks simple, the key is CLEANLINESS and DRYNESS.
The death to it is slow, if one do a bad job. Could be months or years later you get the damage.
Dryness is the patience you must have and a good vacuum pump with good vacuum hose and a micron gauge. 10+ hours of vacuuming on my own car and my friend's car
if done in my home is common.

I made good progress on my AC system, but next year all of its o-rings at TXV and hoses at engine bay ( hot ) and therefore filter drier will be replaced.
It is cheaper to maintain them , than to have to buy 100% of everything when you get compressor black death....yes no joke, AC system of today with micro channel EVAP and condenser and IHX,
you can never remove debris from compressor black death.

Running low on refrigerant alone can kill your compressor, because the compressor oil will get stuck at the EVAP and compressor will be lacking of oil.

Good luck on your AC woks.

 

My 2010 E550 had this problem and long story short, the system was over charged. I let some refrigerant out and it started working fine and has stayed that way for several years since this happened.

My problem surfaced during a very hot day (105F) that I understand caused the over pressure in the A/C system.

 

Who does the charging and get it over charged in the first place ?
Untouched HVAC from factory when filled properly , natural leak thru the seal will be approx 8-10 grams per year.
Typical W212 single EVAP will need 590 grams, typical but not all.

Without using proper scale to 2 grams accuracy during evacuation and charging, there is no way to know how many grams in the system when evacuated,
and what correct amount have been charged back to the system.
Fill capacity by pressure is a NO NO. Troubleshooting using pressure...YES.

Also those small jerk-off cans refrigerant , their refrigerant purity is a big question.
I am lucky I can get 30lbs tank to make sure I get genuine one from the importer, as there is no law in my country to stop me from buying big bottle/tank without HVAC licence/training.

https://www.epa.gov/section608/refri...es-restriction

***** US DIY-ers have restriction *****

The sales restriction is established by EPA regulations (40 CFR Part 82, Subpart F) under Section 608 of the Clean Air Act.
Only EPA-certified technicians are allowed to purchase ozone-depleting substances (ODS) or non-ozone depleting substitutes used as refrigerants, with limited exceptions.
Refrigerant can only be sold to technicians certified under the Section 608 or Section 609 technician certification programs,
where individuals may only purchase refrigerant consistent with the appliances covered by their certification.

The sales restriction covers refrigerants contained in cylinders, cans, or drums, except for the sale of small cans of substitute refrigerants (e.g., R-134a for use in motor vehicle air conditioners).
This sales restriction does not cover refrigeration and air-conditioning equipment or components containing refrigerants.
******

 

To my knowledge my car was in “as made” condition do the overcharge was done by Mercedes Benz when they made the car.

 

Dang !!! Unlucky you.

 

My 2012 S550 is close with refrigerant overcharge too. I have not needed to do anything yet but with 95F degrees this week the fan goes to the max speed screaming when I start the car. It start blowing cool right away though but I know it is on limit and any hotter day I may need to let some refrigerant out.

What happened with my E550 was very clear overcharge of the A/C system.

It is the general belief that when cooling stops the system needs more refrigerant but the cooling also stops when overcharged. The difference is if the compressor runs or not.