Mercedes HVAC

OK, the car sat for 4 years.

Try to turn on the AC gives a blinking red light in the button, and eventually just red.

thought it was a bit low, but the shop (while rebuilding the ABC system) put a bit of freon in it, but no go.



Bought a carsoft II unit and started working the problems. After clearing all the faults caused by low voltage, still having issues.


B31 multifunction sensor read temp and dewpoint

also OCP console under air temp, read 350 N70m1 (inner blower motor temp sensor), and 340 n70b1 (innet air temp sensor)




Pressures should be checked at 2000rpm. Low side about 40, high 250. (need better references)


Ambient temperature can change those numbers though so keep that in mind.


Sensor B12/2 is in receiver drier. Need to recover refrigerant to replace it. Electrically it is connected to left front SAM.


Temp pressure chart




Here's some links I am persuing:



Even after you have the correct amount of refrigerant installed, the compressor won't run until you reset the system.

1) Set the car in park and turn on the engine, hold the rest and particle filter buttons down together for about 5 seconds (The screen will show searching)
2) This screen gives you the fault codes. If you're curious, scroll up and down to see them using the temp up and down switch.
3) Pop out the left "auto" button and right "auto" button.
4) Now press the the left button in, and then the right one. The system will reset.
5) Turn the car off, wait a minute, then turn it back on again. If you don't have any further problems, the light should stay off. (If it comes back on again, you have more things to do).

I suggest that you write down or print out the reset procedure and put it in the glovebox. That will let you reset the system if the refrigerant gets a little low on a trip - your passenger will appreciate it.



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