Working on my sister's W211, and noticed the AC is not cooling as it used to when I drove it back in 2015. It used to be a fridge in the cabin, even cooler than my W212.

Connected the gauges, the iCarsoft scanner and took the following data @2000 RPM

AC setting at LO (display), maximum blower, all vents openExternal Temperature 94.2 F - @ 93 F
High Pressure side 204.1 PSI - @205 PSI
Low Pressure side -142.6 F - @ 45 PSI
Evaporator Temperature 57.2 F - N/A

Not sure if the problem is a damaged B12/2 sensor (-142.6F makes no sense to me), or low refrigerant.

Suggestions are highly appreciated. I just do not want to start adding refrigerant and get a bogus fix.

 

the high side being 205Psi.... means the system is charged up and the compressor is healthy.

There is an inlet proportioning valve on the back of the compressor of these cars that is known to jam... perhaps more so than the TXV.

Arbor-Freight has afordable A/C gauge and vacuum pump if you decide to crack open your sealed lines.

 

Hi Cali.. Thank you for the advice,

Let me read about that valve and see what else I may encounter once I open this AC system, say new drier, sensors, etc.. I am mostly afraid of not knowing how to start the recharging since I read stories about the MB compressor not engaging when the system is completely empty.

I have done partial charging on other brands, and evacuate/replace the expansion valve+drier+condenser in two Toyotas years ago. Except for breaking a seal in my first attempt, everything went smooth and they cooled like a fridge. Great feeling those days.

 

My past 3 vehicles have been Toyota trucks, so yeah. Are you certain the AC system isn't leaking? I own a 2003 E500 with original 56k and tech claims it's leaking. Following.

 

The thing I am certain about is.... that a leaking A/C system has low pressures all around.

Reading good pressures, rules out leaks as primary concern.

Concider other reasons for low cooling, don't just hang on the first one.

Toyota are built from licensing the best German designs.

 

Toyotas are built from German designs? Joke? Technology should be elegant and simple but mostly dependable. None of which are Mercedes. Mercedes are obscenely expensive, ridiculously complex and nowhere near as reliable/dependable as Toyota /Lexus.

 

Perhaps some are interested in this summary:

The above is from research back in Australia, circa 2003.

The key to progress in technology is to stay at the top of the latest concepts (patents available), license them and learn from others. Otherwise, each company has to reinvent the "round wheel" all over from scratch. Once automotive companies understand each other's technology's pros and cons, they can decide how to improve theirs. Difficult to tell who created something first.

 

I am reviving this old thread since the issue is still there. Sis took the car to an Indy a few months back, the system was evacuated and recharged (Indy said "there were no leaks in the system, all good"). She thought it was OK since it was cooling better, but not even close to what she recalls. Since the car is not driven much, it was not a priority until the summer hits

I connected a new set of AC gauges this time and measured them before starting the engine (kjatek1 standard procedure ). The pressure for the low side @112psi, and the high side @113psi with some eyeballing between the gauges marks. See the car's data below. Activated the Climatronic hidden menu by pressing Auto for a few seconds on the AC control panel (which is not the one seen in most youtube videos, or on Ebay). This control panel (which seems to be for a W219 4zone system)


Started the engine, waited for it to warm up, and ran the AC with the engine @2000rpm, the LO setting for temperature in the AC (lowest temperature setting). I also checked the temperature for the rear zones were set to LO as well. Here is the collected data from the climatronic



It is definitely not cooling as it used to. At some point, I was able to see 9 [C] in the evaporator core, but only for a moment (sure it was cooling then). The pressure gauges while running the AC indicated: low side @45psi, high side @170psi-185psi (depending on engine speed). The night data was collected w/o pressure gauges, so I only took data from the AC panel.

I am nearly certain the Evaporator temperature HAS to be lower than 14 [C], I would say less than 9 [C]. Also, I am a bit puzzled by the values of registers 03 and 04. Why would the left side heater core warm up while the right side remained at the original temperature?

I am preparing myself mentally that I may have to check the following:
1 - Solenoid control valve in the compressor
2 - Suction hose from compressor to coupling (related to TSB about collapsing hoses)
3 - Expansion valve
4 - Heater control valve ?

Does anyone have some advice before I empty the system (break the seals as Cali suggested)?

here is some of the documentation I am using as well:
1 - AC sensor locations PDF file
2 - Meaning of the registers of the climatronic https://forums.mbclub.co.uk/threads/...7/post-2180692

 

Juan, long time no see! How are things?


Recently I've discovered how the (W212) HVAC FLAP ACTUATORS are built...

Before you go ahead and open up your A/C , check all your flaps do operate open/close Use a thermometer to compare vents outlets... should be equal.


loose pin connections + dry gears


greased up and soldered


flap modules (5 counts)

Also I found out the HVAC module reads 2x forced air temperature sensors. One near ignition key and one near Overhead Control Panel - - Many things can/do happen with those that cause HVAC to act goofy:

• The tiny fan gets jammed with dust
• The thermistor sensor breakes off
• The OCP posts DATA Temp = "NA"

HVAC defaults to a crazy low temp (-21F) instead of reporting value as being missing with a DTC. Read the data fields!

So long story short...
is simply check your HVAC AAC Module has all correct temps field populated.

The way your pressures are reading good (45/200) make it sound like your compressor valve and TXV are working well. The difference says there is healthy circulation through valves and good pumping.

Cali say do your troubleshooting before you try to get lucky 🤞

 

Hello Cali, all is good over here.. Hope you are doing fine as well. Just busy with work, and the W211 had some hiccups: master window switch died this summer w/o AC, and damaged sunroof motor . Finished fixing the sunroof motor (a vise, improvised bushings with faucet washers , grease every gear inside, and mechanism as well), and it is working perfectly. A new master window switch is in, fixed the rear sun shield, and cleaned the front seatbelts for faster rewinding as a bonus. Now stuck on the AC again. (Sis took it to an Indy for the driver-side fuel "pump"). At some point while testing the AC it was cooling extremely well (9 [C] in the evaporator), then back to bad cooling

Let me read your summary in detail, and see how it fits for the W211. Sis is also having cooling issues with the W166 (which also needs plugs, filters, etc). With work I cannot tackle all at once The W212 is working perfectly, love it.

 

Here is the updated data for today. started sunny but a cloud covered the sun sensors when the engine was hot.

Sun sensor data from the iCarSoft scanner seems correct, All 4 sensors are about the same intensity. I tested the front left and right flaps only, and ignored the rear ones (too many actuators) and they seem to direct the flow to the correct vents, and I can see the values changing in the scanner for each actuator as they are actuated.



For the last run, the AC was freezing cold in the cabin .
Unfortunately, I cannot exactly pinpoint yet what triggered the good run: something is sticking?
- compressor solenoid valve? I did a sudden rev from idle to 3000 rpm, but difficult to tell if that kickstarted the compressor (bmwpowere36m3suggestion in a related thread)
- random pressing of the AC control unit buttons back and for between diagnostic mode, and run mode?
- activating/deactivating recirculation mode?
- not clear why the radiator fan is never demanded at 100% neither by the engine nor the AC at MaxCool nor LO setting. The highest I saw in the scanner was 75%, and I cannot make sense of the climatronic data for registers 10 and 20

The OCP sensor seems to correlate to real data as well.
The scanner Ambient Temperature seems bogus in some views. Some views match the climatronic data (within error), but sometimes is @51 [C] which makes no sense . I think the scanner is taking some ambient temperature under the hood besides the one under the bumper (B14)
There is an entry in the scanner about a request to A9, and it reports 70 regardless of my settings in the AC control unit.

So far, the only excuse I could have to open the system would be to examine/replace a sticky solenoid/expansion valve.
What are the expected temperatures for the heater cores? Is the left core used to dehumidify the cooled air in the cabin? or is the heater shutoff valve stuck somehow?

Need to think it through a bit longer.

 

Juan, great detective job. Your sister is lucky to have you making everything right for her 👍


heater core...

From your data collection, everything looks like it's working BESIDES the heater core left/right: it's dumping heat back into the cabin.
I don't know if the coolant valve may be leaking through or if the flap is letting heat through, not closing, leaking.

You also have a good point about the compressor solenoid being a bit temperamental. Perhaps the car voltage and painted ground are working against PWM signal?
Not all compressors have that control solenoid valve... Your pressure differential look good so hard to pin the issue on the refrigerant circuit.

If you'd stop dumping engine heat, you'd get colder, right ? I'd be looking in that direction...

Wish we could have "BMW_PWR36" star help you... A WIS document on that A/C system would be very helpful too

 

Biting the bullet, and installing WIS today.

I also want to understand what registers 11, 12, 13, and 14 represent. Also, what "*number" means. For example, for the sun sensor (B32/2) the scanner gave meaningful data for the 4 of them, but (assuming those registers are the sun sensors) gave two temperatures and 2 somethings with *. I am afraid that if that means "unavailable" or invalid, the "smart AC' can go wild.

=== Update ===
WIS installed. Learning my way through it .
Getting a better idea of the climate control system, but I have not yet found how to access the hidden menu for the climatronics (hopefully every register is described there)

 

good chance the W211 valve is leaking through!


controls hot coolant circulation

simple test.... if the return line out gets hot/warmed then you know it is circulating through. Use IR thermometer or imaging.
Already the temperatures collected in your spreadsheet make this valve the prime candidate to be feeding heat inside!

 

I was thinking about the valve could be stuck open, but leaking makes a lot of sense as well. Oh my, it means I have to work on it tomorrow and I do not have new push pins/clips for the cowl; otherwise, I will do the windshield washer pump review (not even noise out of it).

 

german failures are well engineered... if this valve is based around a solenoid and a diaphragm, the shaft is basic steel (non stainless grade) that rust as soon as the rubber diaphragm wants to leaks hot coolant. Then hot coolant partially flows through ALMOST GUARANTEED!

Test the return line temperature to know. As far as spreadsheet data: "heater core" should never get hot above ambient with A/C Low, right?

 

Not a good day today for the W211, went outside (102F in the cluster), took the sunshade off and I see the windshield with a hairline crack from the bottom to the top on the passenger side. It seems a small rock chip located @1/4 height from the bottom gave up. .

 

that is no fun, sorry to read that Juan

Better the 211 than on your 212, right?

 

definitely, that is my consolation. Sister took it well, she was expecting the chip someday will give, but we wanted the car back on the road sooner.

Now there is no excuse to take the brittle cowl cover for the heater control valve. It is coming out anyways. Wonder if you know an alternative to replace the rubber strip along the cowl cover w/o a new cover, assuming the cover does not break to pieces when removed. The strip is already all cracked

=== Update ===
Looking for a T or Z-shaped rubber seal, I came across an already proven alternative in another MB forum,
https://www.benzworld.org/threads/re...or-20.3068290/

 

I've not been in there yet!

While the cowl plastic cover is off ...

1-- Test for water leakeage and overflow into HVAC track, into F-SAM and onto both footwells.

2-- Lubricate windshield wipers mechanism and smart motor gearbox. Inspect LIN circuitry for wannabe loose pin. Weatherize PCB with conformal coating.
3-- Check nearby painted GND (wipers,...)

4-- Rain channel rubber outlets have not melted shut

 

Update:
1 - Windshield to be replaced next week, mobile service
2 - Bit another bullet, and also installed Xentry Passthru 2021.6 (I should have done that long ago ). Unfortunately, I used a non-touchscreen laptop but I will clone the installation into a spare touchscreen one with a stylus pen as well (not a fan of the touchpad sitting in the car)
3 - Scanned both 211 and 2124 - Deeper testing of W211 components clearly shows the heater motor shut off (heater control valve) is DEAD, so ordering it today. Also, noticed some settings for the AC were not as expected: 20% Suction Fan setting (moderate climate) instead of 40% Suction Fan value (hot climates and MAXCOOL feature).
5 - while testing activation of AC motors, and testing heating (which of course failed) and others, I nearly got frozen (5 C in the evaporator at some point), so it is definitely not the heater control valve, the system is perfectly charged and the compressor can do its job when allowed. Either the "radiator/suction fan" increased speed for MAXCOOL, or a delay in the compressor (solenoid valve) to actuate at the requested load.

NEXT:
- retest with new "radiator/suction fan" setting (40% hot climate/MAXCOOL default) parked under the sun, not even a shadow from the house from cold start until it warms up.
- explore Xentry further (learning curve), and definitely check every single module of a 14-year-old car.

 

Short update:
1 - Using XEntry tested every single module listed, and deleted stored error/event codes (none related to AC though).
2 - Waiting for the heater control valve, I will replace it once the cowl is out for the windshield.
3 - The AC does not cool unless I set it to LO, or (I think) the voltage is above 14V. At idle the car tends to stay around 13.8/9V and once I increase the rpm's it can go to 14.1/2V. I noticed (unless I am dreaming) that once it hits 14.xV the air out of the vents gets cooler, the cluster flickers very quickly and it seems brighter.

I am starting to wonder if the "delay cooling" is because the computer/control unit is disconnecting the compressor under 14V. The alternator module test passes with flying colors. The battery is definitely at 12.4V with the car off.

I wonder if I should connect either the battery charger (or the CTEK maintainer), check the cluster/Xentry voltage readings, then start the engine and only turn the AC on if it is above 14V and see if it cools quickly w/o me messing around with the settings. Am I chasing an AC symptom of a voltage regulator worn out, or poor grounding somewhere?

 

Juan, sorry to see your sister car has you stomped. It's a great trainer for W212. Use Xentry to read the AAC module data and understand what's happening.

Questioning voltage supply:
I don't think crappy voltage is involved in making the A/C performance lazy.
You have near 14V or better! 👍
Even near 13.1v under a heavy load you'd be okay if ALT is supplying and not draining system batt flat.

Cabin air circulation:
Let's remove the cabin filter to rule that out. Hopefully the evap itself is not partially plugged up by dust bunnies.
How would you say is the blower speed? Does speed ramps up/down auto with temp demand? no missing speef steps, right?

Temp stress testing:
Now observe the evap temp vs. outlet temps when you vary blower speed manually...
-- Can the compressor/TXV keep up with demand with a cold evap?
-- Let's try to understand what happens when requesting LO (non stop compressor?)
-- What happens to pressures ...

Tiny fanned sensors:
While trying to explain difference between normal vs. LO A/C, normal is going to regulate cabin temperature with many-many sensors. Let's just consider the two ambient sensors that use a tiny fan to circulate air over thermistor. These tiny fans get plugged by dust in a hurry. Located near the IGN SW + hosted by OCP.... clean 'em and read them live.

Poor cooling while stopped:
If cooling is affected by parked vs. drive condition then wrap the high side line to keep engine heat from climbing back in the curcuit.

New heater valve:
Hopefully this will bring your heater core back to base ambient.
-- Can you spot any obvious core temp difference between old vs. new coolant valve?

Solderless in w212 A/C:
I can't say for sure how many solderless modules MB planted in the W211... these chassis tend to remain extremely similar
The W212 AAC controller + all flap actuators use the amazing pressed pins. The facelift blower speed regulator is good but located in a swampy area with wetness & corrosion opportunities.

Delayed cooling:
The AAC may be sensing a high moisture over windshield ...

solderless HUMIDITY sensor

Somewhere else I wrote about drying the wet A/C section with heat. This prevents foging up the windshield based on measured humidity sensor. The AAC logic may be acting on faulty or missing sensor. (Ex my personal OCP has gone silent)

Hopefully we're not just dealing with overcharged circuit like this guy recently that was at 350psi

Hope this helps you stay cool, si no... cervezas!

 

g​​​​​​eneric chart spoted from @bbirdwell of Texas.


not cool

If we succeed in getting your A/C cooler, we can get ours too 🤘

 

Update:

1. Installer brought wrong windshield for panoramic equipped vehicle
2. finally installed heater control valve, Xentry error went away,
3. Tested heating, though not needed in the Florida summer, and now works
4. Monitored hidden menu, and registers 03 and 04 are different as the car warms up. Wonder what they really represent
5. Foam cleaned condenser as well
6. Xentry tested ACC module, and all diagnostic seem plausible, AC seems to be cooling better and consistently , but not like the W212

TODO:

• remove AC blower and check evaporator for dust/clogging
• Likely I will foam clean it as well
• Retest, and document carefully.
• Drive it the more often to check variability, brother is visiting so getting unbiased feedback
• Update on progress