Compressor not engaging

BLESSING EWOBOR

MEMBER
2012 MERCEDES BENZ GLK 350
6 CYL
AUTOMATIC
208,543 MILES

Hello, I am working on vehicle, the compressor is not engaging when the button is pressed. I have checked for fuse and relay they are in good condition. I connected the compressor directly to the battery, it work perfectly so the problem is not the compressor. I don't know if I could have the circuit diagram on the air-conditioning system.

Wednesday, September 23rd, 2020 AT 12:52 PM

2 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I am not a big fan of Mercedes Benz's manuals but this one is not too bad. The way this system works is the front SAM control unit sends power to the compressor when it gets the input from the button and the pressure sensor says it is okay to turn the compressor on.

Unfortunately this is a 3 wire sensor and cannot just be jumped to find out if the compressor comes on. The way to find out if the sensor is functioning is to monitor the SAM and see what it reads as the pressure. Then match that to the actual pressure on the A/C gauge set.

If this checks out then I would think the SAM is the issue.

Images (Click to make bigger)