[rnguyen513]

Hi,

I'm in the middle of an A/C job, and I suspect that there is some electrical fault with either the front SAM unit (N10/1) or C-AAC (N22/7). Based on the recorded SAM error (code B1046), it thinks there's either a short or open connection to sensor B12/2 (refrigerant temperature and pressure sensor). Shockingly, live data showed that the refrigerant temperature was 255 Celsius (as read from the SAM) and ~6500 Celsius when read from the A/C module. I'm not sure why the two modules would report different readings for the same sensor, but these are clearly invalid. Though I feel it's possible this is the cause behind the inoperative A/C system, there are also reasons that this may not be the fault:

-Excessive temperature reading would force the engine fan to 100% constantly, which is not the case--the fan runs normally under load.
-Temperature/pressure sensor B12/2 was already replaced when a new condenser was installed, so there shouldn't be any issues with the sensor itself.
-Invalid readings such as these extreme temperatures can just suggest that the vehicle model isn't equipped with the sensor, so my "temperature sensor" could be nonexistent to begin with.

All I can think of now is some kind of faulty connection between the sensor and SAM or C-AAC, perhaps water damage or some kind of miscellaneous engine wear on the connection. I will check the connections at the bottom of the SAM for corrosion, but does anyone know how the b12/2 cable is routed and what it looks like? Other than this, there are no relevant faults that would impede an otherwise working air conditioning system.

Let me know if there is missing information, thank you.

 

[RealDonn]

Maybe a reset will help. From a discussion here some years ago, see the 2nd comment from the very knowledgeable rudeney: clk500 heater/ ac problem

 

[rnguyen513]

Maybe a reset will help. From a discussion here some years ago, see the 2nd comment from the very knowledgeable rudeney: clk500 heater/ ac problem

I've tried the reset, but to no avail (the lights keep flashing continually). I didn't mention that the car also has several faults with the left and right footwell flap actuators (M2/15 and M2/11) because they are stuck, so this is likely what's causing the reset to fail and run continuously. This shouldn't be stopping the compressor from working though, right? And I see that there's a procedure for checking sensor data directly on the AC control panel, should I try this or is it the same as reading live data from the C-AAC from a scanner tool?

Also, is it true that the "AC OFF / REST" button on the climate control panel is needed to be on for the compressor to run, instead of shutting it off like the button suggests?

 

[rnguyen513]

I put the climate control into diagnostic mode and here are the results:

00- 77
01- E
02- 73
03- 17
04- 80
05- 80
06- 70
07- 4
08- 32
09- 0
10- 35
11- 0
12- 0
13- 0
14- 0
15- 0
16- 41
17- 91
18- 69
20- 40
21- 65
24- 41
40- 66
41- 00


Code 01 is for cabin temperature, and I assume that the E means error? Other than that, are all other readings plausible?

Thank you

 

[rnguyen513]

there are also reasons that this may not be the fault:

-Excessive temperature reading would force the engine fan to 100% constantly, which is not the case--the fan runs normally under load.
-Temperature/pressure sensor B12/2 was already replaced when a new condenser was installed, so there shouldn't be any issues with the sensor itself.
-Invalid readings such as these extreme temperatures can just suggest that the vehicle model isn't equipped with the sensor, so my "temperature sensor" could be nonexistent to begin with.

Update: purging the refrigerant lines and inspecting the B12/2 via diagnostics showed that the sensor itself was not working and causing the error within the SAM. It turned out that the replacement condenser B12/2 was only a standalone pressure sensor, and was not equipped to read temperature data for some reason—I figure that the donor car had a separate temperature sensor located elsewhere in a more conventional spot unlike the w209.

Still though there is no cold AC, and the only remaining faults left to tackle relate to the secondary cabin temperature sensor which is located within the overhead control panel. Some time ago my clk experienced flooding via the sunroof which put the OCP (N70) out of business, so this fault with the cabin temperature sensor makes sense. I have yet to diagnose the CAN and power to the OCP, but the unit will likely have to be replaced as it does not communicate whatsoever.

Backtracking a bit though, would an invalid cabin temperature halt the ac from running? Also, is there any way I can noticeably tell that the compressor is on and working? Can I force it to start by connecting voltage to its input signal line?