SL AC Troubleshooting



AC Off light kills AC operation. Codes B1000-001 B1256-001 Malfunction in refrigerant circuit HOW DO I FIX? or Faulty Control Unit



How do I fix a malfunction in refrigerant circuit or faulty control unit indicated by AC codes?



Is there a sensor to replace? A short to fix, oil in a connector, a bad connection, anything simple? Is there a troubleshooting guide, circuit diagram, diagram of AC (Air Conditioning) components, something useful?



The AC works perfectly until the AC Off light comes back on. The refrigerant level is measured - optimal.



When I erase codes with My Autel Diaglink, the AC Off light turns off; and the AC works perfectly. After I turn the car off and on a few times, the AC Off light comes back on; the AC quits blowing cold; and I read the following codes:



B1000-001 Stored

The control unit is faulty.

B1256-001 Stored

Malfunction in refrigerant circuit



From my signature, see this is a 2003 SL500 USA model.



Thanks in advance guys!

Thom

Since the A/C is properly charged, the evaporator temperature sensor is suspect. Use your Autel to read the evaporator temperature being reported to the in-dash controller. Since the sensor is wired to the driver-side SAM, you do it through that controller's diagnostics.

Incidentally, this is the forum for the 129 SL models.

Thanks bobterry,
Your comment about how to use the Autel Diaglink is especially helpful. It has been good for clearing Diagnostic Trouble Codes that you normally have to have a dealer to clear for you. I cleared the codes for all of my systems multiple times, re-clearing especially AC codes after the trouble light came on. The light disappeared. I sometimes will ask for help on forums other than this site’s R230 forum.

Hi Bobterry,



I just ordered the “For 2003-2006 Mercedes SL500 A/C Refrigerant Temperature Sensor 74425WH 2004 2005

Seller: autopartsgeek

[img]file:///C:/Users/HEARIN~1/AppData/Local/Temp/msoclip1/01/clip_image001.jpg[/img]

https://www.ebay.com/itm/For-2003-20...8AAOSwb91dZn6n
It goes above the dryer. Do you just unscrew old sensor above the dryer, and screw in new sensor with minimal refrigerant loss? If not how do I replace it?

Here are the DTCs. Is sensor 1 the previously purchased For 2003-2006 Mercedes SL500 A/C Refrigerant Temperature Sensor 74425WH? If so, can I just unscrew the old one, and screw in the new one? Or will unscrewing the old one purge all of the refrigerant?
09152020 from Diaglink:
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).

here is another code entry:
Event memory
B1059-001 Current
Fault in CAN communication with control unit Driver signal acquisition and actuation module.

Is this refrigerant sensor1? If so, how do I replace it? Can I just unscrew the old one, and screw in the new one? Or will unscrewing the old one purge all of the refrigerant?