My 03 SL55 has weak air con output. The car has only 63k on the clock. I had it regassed (it had about a third of its coolant) but the output is still just below ambient temp. There is no leak and the unit held a vacuum fine. The condenser is cleanish looking.

Star does not report any faults and it passes the test.
It comes at a bad time as my S211 has eaten its compressor clutch so that needs replacing as well!

Any ideas very welcome.

 

Same issue with mine- I had freon, lines, compressor etc checked out and everything was fine. No fun on 90+ degree days- AC output feels like 68 degrees when i have it set all the way down to 60 degrees. I have it on blast- knob is turned to the half way mark just so I can stay somewhat comfortable. Given the small space, you would think the inside would cool quickly.

Also noticed that when I first start the car and turn on the AC, it blows out hot air for the first 20-25 seconds and eventually starts to get cold. Maybe its by design but on my lexus, the AC is instant.

 

I have access to two 2005 SL500s. One the AC comes on almost immediately, the other the AC sometimes takes a long time to engage. Once the slow one engages, it works normally. I can tell the electronics making the slowness because it lights up "max cooling" when it activates, nothing before. I know it isn't supposed to be slow as the other car is immediate, but I have no idea what is wrong.

I've found that cooling improves dramatically if I downshift to get the RPM up a little. These cars run at such a low RPM at slow speed, I think the AC has trouble.

Hopefully someone here know what is going on.

 

With Star Diagnosis I would connect to the climate controller. From the main menu I would choose Actual values and look at the plausibility of the ambient air and vehicle interior temperatures. I'd also check the refrigerant pressure; it should be at least c. 14 bar. If those checks pass, then next I'd look at compressor control.

I believe the compressor is designed with the objective to drive the evaporator temperature to a few degrees above freezing. So, I'd compare the evaporator temperature with the control signal to the compressor. For no apparent reason the compressor control seems to never exceed 70%. If your compressor is running at 70% and the evaporator temperature is nowhere close to the target, then this suggests a problem with the refrigerant circuit, and I think you might want to measure the low-side refrigerant pressure to troubleshoot.

 

A/C Pro has a guage on it's refrigerant fill kit that is really easy to use. Just clip hoses to ports. The needle points to ranges: low filled yellow and red. I bought the one that does not require a refrigerant can to be attached to get a reading. see:
https://acprocold.com/ac-pro-instructions/

 

not very similar, but my issue is that the central two vents do not work (no air output). only the two at both ends of the dashboard, and the foodwell airvents work.
the center dials do nothing (closing or opening them does not change air output).
any tips on what the problem could be?

 

The center-dash control unit is wired directly to the pushbutton controller in the dash. Problems could be with either control unit, a stepper motor, or a mechanical defect in a air flow control flap. A $250 Star Diagnosis System can quickly and effortlessly narrow down possibilities if not pinpoint the cause of your problem.

 

Sorry rawhide, but if you had to add that much freon, your system has a leak. Freon doesn’t just disappear.. it’s a sealed system. The only way you lose freon is via a leak..if a car is not driven often with A/C RUNNING, seals and/or O- rings can become hard and leak freon. When system is running again, maybe after not being driven for a while, the freon and oil begin lubricating the seals/O- rings, making them pliable and resealing the system.. short a few ounces of freon.. just enough to cause A/C to under perform. With R134, just a few ounces short or a few ounces overcharge can cause Performance issues. To get the precise amount of freon, it’s a good idea to totally evacuate and then add exact amount of freon to the system, usually done by professionals with proper equipment.

 

As an update to this I have run a test in STAR. The unit again shows no faults. However I have noticed in the refrigerant compressor menu the compressor shows as off. I can manually activate the compressor from STAR and it blows lovely and cold from the centre vents immediately. I hear the compressor activate so I know the system does work. The pressure is around 12-16bar at idle speed.

This is good but I am none the wiser as to what to fix next.

 

But in your screenshot the compressor is on, so I can draw no conclusions from the data shown on the PC screen.

 

Hi Bob, that menu allows manual activation which I had done. So I know the system works ok its just something is not turning on the compressor during usual operation.

Your help as always is really welcome!

 

This i think was the screen prior to manual activation

 

All of the sensor values are logical. With the evaporator temperature at 24 degrees C. the controller should be signaling for the compressor to run until the temperature approaches zero. The only explanation I can think of is that the AC-OFF button is on. For the compressor to operate the LED on the button must be off. If yours is, then verify the LED works by pressing the button.

 

Hi Bob, you might be onto something here. When I bought the car one of the first things I did was install a bluetooth dongle which I hardwired to the 12 power outlet in the glovebox. I'm wondering if perhaps I disturbed a plug which means the A/C button no relays a signal to the compressor. I really don't fancy taking the trim all out again to test this theory though. I was pretty careful and all the other controls work just fine so I'd expect that to be unlikely.

When the button is pressed the LED does go on (red) and I acknowledge that this switches OFF the AC. I have heard somewhere this logic was reversed on a later car I think.

 

As an update to this I had my local AC specialist look at the car today. After spending a good couple of hours the only issue we could find was erroneous values reported by the 'multifunction sensor (2118300472). It was showing negative values whilst the ambient was around 28c and the engine bay very hot. When heating the module with a hairdryer the reported temperatures dropped which is not expected. The only other thing is when manually activating the compressor with diagnostics the evaporator temperature got a bit high for his liking. He told me the fan should be working a bit harder but was not. Perhaps overgassed system or maybe not a problem.

I've order a used sensor and will see if this helps but if it does not he honestly does not have an idea what to try next. He advised on an SLK the system should run with this sensor disconnected but that was not happening on my car.

 

Definitely let us know how it shakes out

 

What codes did your guy read?

 

Hi - the car is not throwing any codes. We were only able to make assumptions by reading the live values of the sensors. New (old) sensor arrives tomorrow so fingers crossed.

 

I pulled a reading of 3698 psi at the sensor:
182 B12/2 (Refrigerant pressure 255.0 bar
and temperature sensor) Pressure value

Does this mean the Refrigerant pressure and temperature sensor is faulty?

See the codes and event memory below:
Read Codes
B1337-002 Stored&Current
B12/2 (Refrigerant pressure and temperature sensor 1) ( Refrigerant temperature ):The component is faulty or the lead has Open circuit.B1338-002 Stored&Current
B12/2 (Refrigerant pressure and temperature sensor 1) ( Refrigerant pressure ):The component is faulty or the lead has Open circuit.
B1341 Stored&Current
Fault in communication with component H3 (Alarm signal horn).

Event memory
B1059-001 Stored&Current
Fault in CAN communication with control unit Driver signal acquisition and actuation module.

 

Thanks for the help guys!

Hydraulic oil may have fowled up the Refrigerant pressure and temperature sensor.

I spoke with a great mechanic yesterday. I showed him the codes and Diaglink data. I explained to him that I added 2 cans of refrigerant. He asked if I had oil in the sensor. I told him I cleaned hydraulic fluid out of the sensor and connector, got the compressor working, then added refrigerant. He confirmed that the sensor I ordered is the right one. He thinks the hydraulic oil caused the problem; and I compounded the problem by adding refrigerant after I cleaned oil out of the sensor and connector.

He proposed to evacuate the refrigerant, clean the sensor, and fill the system properly. I will wait and check readings with the new sensor connected to the wiring connector, and not installed on the dryer line; and see if the pressure reads zero, check the remaining codes, then try his solution. I may not even need the new sensor. I cleaned the sensor and connector again, and removed the wicking cloth tape around the wires. So, he may just need to correct the refrigerant level.

Some of my old readings 6 months ago show 9 bars pressure. Today it shows 555 bars pressure. I probably overfilled it. But that super high reading seems like the sensor is messed up. About 6 months ago I had hydraulic fluid reservoir burp up quarts several times before I fixed the suspension. Fluid wicks its way up cloth tape into sensors.

The sensor won’t arrive until next week. If the diagnosis and solution are not as described here, I will let you know.

BTW I attached the ACPro gauge to the low pressure side. The gauge was in the green. I added (2) 12 ounce cans of R134a. The gauge stays in the green while the sensor reading is 255 bar or about 3,700 psi.

 

As an update to my issue my sensor arrived today but I realised in error I bought the wrong sensor. I ordered 2208300171 whereas according to STAR my car needs the 2118300472 sensor. I tried the sensor but it seems to report an error on the dewpoint reading (again) which is odd. I replaced my original sensor which is a bit dirty and makes me wonder if someone had already tried to replace it before my ownership and it was reading in STAR values which seemed normal. However whilst I'm not getting any error coded with the AAC systems I'm still not getting compressor activation except when manually activating the compressor using STAR.

I've ordered another 2118300472 sensor to see if that helps. (used again). They are cheap and plentiful so no need to buy new if this is the problem.

I've been testing all the other sensors to see if I can find anything else as my AC specialist was not an MB guy so used his own scanner. I've also noticed sensor B11/1 (Coolant temp sensor) is showing a value which is not o.k. so perhaps more to look into.

As always knowledge is welcome as my AC specialist has essentially given up so next step would be an MB specialist if I can't fix on my own. I know the system does function mechanically as that has all been confirmed.

 

Hello Rawhide - did you ever figure out your AC issues? Mine is also not blowing cold air and shows low on refrigerant per my AC recharge can/tool. It wont take the AC recharge though as I attempted to fill it for 2-3 times but no refrigerant is going in.

This is the only code that I am experiencing and cannot find much info on where this CAN / control unit is or if it needs replacing. any help would be greatly appreciated.

B1059-001 Stored&Current
Fault in CAN communication with control unit Driver signal acquisition and actuation module.

 

Unfortunately I sold my car before I fixed this issue. The next steps according to the STAR procedure was to start testing sensors which were inside the dash area which was not fun to take apart. Your problem does sound different to mine as I was able to get the air blowing ice cold when activated manually in STAR.

 

I have the exact same prob, I think its the multifunction heater unit.....