My 1999 SL500 has a great air conditioner but it only blows air through the center ducts. Hardly anything comes through the side ducts. I took it to one guy and he thought the module needed to be replaced. Has anybody else experianced this? Any suggestions? Any help will be appreciated as it's 115 here in Palm Springs today!

 

R129 Climate problem

Hi all,

Hopefully this might solve your air-con problem as it did mine.

For a year, I battled with an air conditioning problem. Air stopped venting into the vehicle after 30 minutes or thereabouts, even though the fan was running and I could feel hot or cold behind the vents when I changed the temperature.

To cut a long story short, I got the following advice. Turned out to be a sensor. My local garage were a bit reluctant when I told them exactly what I wanted doing, but below is the advice I was given - it saved me changing the heater control panel (garage advice) and it has worked fine ever since:

---------------------------------------------
Service operation: 83 8054 01 "Temperature sensor on evaporator replace"
Part number: A 210 830 07 72 "Temperature sensor"

Sounds like your evaporator temperature sensor has failed. This causes the evaporator to ice up. You can check it on the pushbutton control module. There is also a technical bulletin about this problem.

It is a very cheap and easy repair. New sensor is about US$50 and can be fitted in the blink of an eye.





You can test the evap temp sensor using the diagnostic feature on the a/c push button control unit.

Come to your car in the morning or when it has been standing for a few hours (so the engine and heater are cold). Turn the ignition on, without firing the engine. Run the self-diagnostic routine on the air con pushbutton control panel and check the evaporator temperature reading. If the sensor is faulty, you will have a logically impossible value:

1. Turn ignition on (without firing engine)

2. Set the air con temp to 72 deg F or 22 deg C

3. Press "REST" for more than 6 seconds

4. The left side of the display will alternately display "01" (which is the test number) and the cabin interior temperature (eg 72 deg F or whatever the temp in the car happens to be).

5. Press the fan speed "+" button to advance to the next test (eg "02").

6. The evaporator temperature is test number "05". The working temperature of the evaporator is between 2 deg C and 12 deg C. Obviously, if your car has been left overnight and has not been started, the value returned should be consistent with the ambient exterior temperature. So if it is about 12 deg C outside, the sensor should return about 12 deg C also. If the evaporator temperature sensor is broken it will return a logically inconsistent value, eg 40 deg C.

7. Now turn on the car and run the a/c for a few minutes. Repeat the procedure above. Test "05" which is the evap temp sensor, should return a value of 2 to 12 deg C if it is working. If it is broken, it will return an impossible value, such as 40 deg C.

The other tests on the push button control unit are great:

01: in car temp sensor
02: outside temp sensor
03: heater core temp sensor
05: evap temp sensor
06: ECT temp sensor
07: refrigerant pressure meassured in BAR
08: refrigerant temp sensor

21: engine speed
22: vehicle speed

There are loads more.

Part No. 2108300572….or 1298300072

Heating and ventilation …heater case


Service operation: 83 8054 01 "Temperature sensor on evaporator replace"
Part number: A 210 830 07 72 "Temperature sensor"







Nr. Description Unit

01 In-car temperature sensor °C
02 Outside temperature sensor °C
03 Left heat exchanger temp. sensor °C
05 Evaporator temperature sensor °C
06 Coolant temperature sensor °C
07 Refrigerant pressure bar
08 Refrigerant temperature sensor °C
09 Not assigned --
10 Blower control voltage Volt
20 Auxiliary fan control current mA
21 Engine Speed x100 RPM
22 Vehicle Speed km/h
23 Circuit 58d (% of batt. Voltage) %
24 Battery Voltage Volt
40 Software staus
41 Software staus
42 Variant Code 1st numerical value
43 Variant Code 2nd numerical value
50 Not assigned
51 Not assigned
52 Not assignd
60 Roof OPE/CLO
61 Left side air outlet, knurled wheel
potentiometer Volts
62 Vacuum actuator 46, feedback
potentiometer Volts
63 Center outlet, knurled wheel
potentiometer Volts
64 Vacuum actuator 47, feedback
potentiometer Volts
65 Right side air outlet, knurled wheel
potentiometer Volts
66 Vacuum actuator 48, feedback
potentiometer Volts

Item 63 is the input signal from the thumbwheel control for the center vent, and 64 is the feedback signal to the controller giving it the position of the vent flap. As you move the thumbwheel these values should continously vary from a minimum of roughly .7 to 4.5.

The original part number was A1298300072 - it has been superceded by A2108300572 which is £28. It is located under the dash on the drivers side by the centre console housing - you just need to drop the trim panel for access.

 

I had a similar problem on my 2000 SL500.

The vacuum hose was disconnected.
Apparently this happens over time. The hose expands and gets loose or the length contracts and it pulls off.

The hose usually disconnects under the bonnet but sometimes this happens under the dash.

 

Running the info scan on the AC screen was great info!

 

Last winter the heater blower on my 97 SL 500 stopped working. Now it seems the a/c is cooling through the vents and the blower will start running randomly.
I just replaced the climate-control in the dash but that evidently wasn't the problem. Any suggestions on diagnosing the problem would be greatly appreciated.



Ben

 

Hi malcolmam, thanks for the great post, I am having exactly your symptoms, I ran the test and sure enough my sensor was reading 51 C while off and got down to 47 C while running. I have ordered sensor and I'll post how I go! Mechanic was also surprised that this sensor was causing that problem but it must screw something up in the control unit.

 

Any update on this?

 

Hi Vander,

Yes, update is it all works perfectly now. All the sensor readings come through within the correct range and that was the fix! Just a tip for people on the left side of the road though, with LHD the sensor is located on the left hand side of the tunnel on the drivers side, THIS POSITION IS THE SAME on RHD, so it is even easier to change, you just drop the carpet trim on the passenger side and there is nothing blocking you and boom you swap it out in about 20secs.
I made the mistake of searching under the drivers side for ages wondering why I couldn't find it!

 

I had the same problem as Malcolmam with the air con or heating cutting out after 20 mins or so. Spent over £1500 at Mercedes over four years to absolutely no effect.
Saw the post from malcolmam, booked the car into an air con specialist to have the evapourator and ambient sensors replaced (total cost £150) and now the system (after 4 years of torture and expense) works perfectly.

Such a useful post. Specialist mentioned that both sensors seem to have to be working properly as they seem to communcate with eachother.

 

Amazing the amount of diagnostic info this can read - thanks !!!

 

Having this exact issue with my new, to me, sl I just picked up. Dealership is taking care of problem since they missed it, but sounds like this is their fix. First night I had car I had to drive home from gf's parents with the top down since I'm new to convertibles and about 10 miles in heat stopped blowing. Was a cold 30 miles. I get nothing from center or floor vents.

 

I have a 99 that is new to me. First day it was warm enough to use AC I discovered it didn't have any. There is no EC light on so I had assumed it was OK. What code would I look at to see if there is refrigerant in the car? Anyway to cycle the AC clutch?

 

My '99 didn't blow cold the first time I tried it either. I bought a do-it-yourself recharge kit from the parts store, and that fixed it right up. It only cost $30 and took about 5 minutes.

 

Do you know what the pressure in BAR should read? Also how can I get the AC clutch to engage if the pressure is too low to activate it?

 

I don't know what the pressure should read. The kit has a pressure gauge on the can that goes from green (good) to red (bad). The instructions with the kit said that if the compressor wasn't kicking off, to shoot about 1/2 of a bottle of the refrigerant into the system, and then check to see if that gets it going. I also looked at a couple of you-tube videos of other people doing this before deciding to give it a try.

 

Hi, Well press and hold the rest button for 5 seconds, when the system goes into diagnostics then push up fan button until 07 displayed and that will be the pressure in BAR

 

I put a gauge on the AC and it had some pressure, I cleared codes and added a can of 134. Still not very cold. Can someone tell me what the values should be in test mode? ECT and evap and what ever it checks?

 

I cannot find a way to access the pushbutton AC diagnostics to match my 1994 SL 500 (129067). Holding "REST" does not do anything. Need to get to 05 (evaporator temperature) to Check if sensor is operating properly. AC cuts out for no apparent reason after running an hour or more. New Compressor and fully charged.

 

Additional info. Pressing "REST" with ignition off or on brings same result. Temp shows 22 C and fan runs, even with key out of the ignition. Very frustrating. Has anyone had this experience.

 

Where is the vacuum line that can be disconnected? Cannot find schematic of the unit on line. Thanks

 

All of the diagnostic manuals are at www.manual.startekinfo.com. The one for the climate control includes a schematic and is here: http://manual.startekinfo.com/manual/JSP/cc/3_8/m31.jsp.

 

Thank you, will be very helpful.

 

Excellent info malcomam - Thanks !!! Added some 134 with sealer, still running cold...
Mechanic says older cars build up leaves, etc. in evaporator, turns to mulch and is acidic, corrodes evap - probably needs replacement eventually...

 

Great AC info. No issues on my 2000 SL500 but I assume that the diag steps are the same?

 

Probably...