Another Car, Another Climate Issue. AC This Time. Topic is solved

[xanthefin]

From App check Live - Motronic - what does the A/C pressure report?

[abscate]

Can’t access my Alldata when cruising the Mediterranean so using your diagram

Key on

Check for 12 volts at the two indicated terminals to see if the system is powered up

If good, ground the indicated terminal to trigger the relay, bypassing module 4/46 and seeing in compressor kicks on.

Note that both pressure switches input to module 4/46, so bypassing them to test pullin also presumes the module is effective, troubleshooting requires you isolate components without such assumptions.

[V50M66]

From App check Live - Motronic - what does the A/C pressure report?

App is showing -175 kPa (engine off, compressor off obviously, full charged system). Certainly seems like that's not reading correctly.

[abscate]

Probably need key on to power up the 4/46 to get a real Measurement there.

The high pressure switch is dividing a base voltage to give a voltage proportional to pressure, if the voltage isn’t stable the reading won’t be meaningful

[V50M66]

Probably need key on to power up the 4/46 to get a real Measurement there.

The high pressure switch is dividing a base voltage to give a voltage proportional to pressure, if the voltage isn’t stable the reading won’t be meaningful

Yes, key was in pos II so ECU was powered on and reading correctly as far as I can tell. I'll swap the switch and see if I get a different result

[xanthefin]

I say as heads up that -175 technically is zero in raw measurement value what Motronic indicates and its just conversion which makes it to -175 currently. I at one time have determined it to be like that but i am listening.

Edit: Okay found it.. to force AC Relay on toggle of Motronic M4.4 through OBDII without engine running .. copy paste in app Service terminal box and press send:

ATPC
ATL1
ATS1
ATSP 3
ATH1
ATAL
ATSR 13
ATE0
ATIIA 7A
ATWM 82 7A 13 A1
ATSI
ATSH 85 7A 13
B0 1D 32 FF


Now A/C Relay gets 12V from Motronic B:40 Pin (Grounding) pulssed.


To stop pulssing just write

B0 1D 00 FF

and press send.


At minimum you should hear A/C Relay clicking. I tested on bench.
If you dont "pressostat AC" component is in middle of M4.4 Pin B/40 and AC Relay current path. Short it. This seems be for old design. Ignore

[yanga001]

So 98's were a bit finicky when i played with the AC.

I had an MCC too and one thing I had occur before was i tripped the pressure switch which would prevent any clutch activation of the compressor. Once i cleared the code the compressor would behave as per normal.

If you are not seeing the code then its probably fine. Its been a few years but i recall using VOLFCR for clearing out the code. I dont think i got a chance to test it with my foxwell scanner.

Other issues ive had with the MCC is that the AC push button developed a cold solder joint and would not engage unless pressed hard. Resoldering fixed that issue. I dont suspect you have that issue given you swapped mcc's.

[V50M66]

I say as heads up that -175 technically is zero in raw measurement value what Motronic indicates and its just conversion which makes it to -175 currently. I at one time have determined it to be like that but i am listening.

Edit: Okay found it.. to force AC Relay on toggle of Motronic M4.4 through OBDII without engine running .. copy paste in app Service terminal box and press send:

ATPC
ATL1
ATS1
ATSP 3
ATH1
ATAL
ATSR 13
ATE0
ATIIA 7A
ATWM 82 7A 13 A1
ATSI
ATSH 85 7A 13
B0 1D 32 FF


Now A/C Relay gets 12V from Motronic B:40 Pin (Grounding) pulssed.


To stop pulssing just write

B0 1D 00 FF

and press send.


At minimum you should hear A/C Relay clicking. I tested on bench.
If you dont "pressostat AC" component is in middle of M4.4 Pin B/40 and AC Relay current path. Short it. This seems be for old design. Ignore

Perfect, that worked. AC relay is clicking, compressor shows engagement and disengagement along with relay clicks. This seems to confirm that circuitry is good.

Tested the AC pressure again, this time with the engine running and a new sensor. Looking at 392-405 kPa. Compressor still will not click on under normal operation.

[yanga001]

I say as heads up that -175 technically is zero in raw measurement value what Motronic indicates and its just conversion which makes it to -175 currently. I at one time have determined it to be like that but i am listening.

Edit: Okay found it.. to force AC Relay on toggle of Motronic M4.4 through OBDII without engine running .. copy paste in app Service terminal box and press send:

ATPC
ATL1
ATS1
ATSP 3
ATH1
ATAL
ATSR 13
ATE0
ATIIA 7A
ATWM 82 7A 13 A1
ATSI
ATSH 85 7A 13
B0 1D 32 FF


Now A/C Relay gets 12V from Motronic B:40 Pin (Grounding) pulssed.


To stop pulssing just write

B0 1D 00 FF

and press send.


At minimum you should hear A/C Relay clicking. I tested on bench.
If you dont "pressostat AC" component is in middle of M4.4 Pin B/40 and AC Relay current path. Short it. This seems be for old design. Ignore

Perfect, that worked. AC relay is clicking, compressor shows engagement and disengagement along with relay clicks. This seems to confirm that circuitry is good.

Tested the AC pressure again, this time with the engine running and a new sensor. Looking at 392-405 kPa. Compressor still will not click on under normal operation.

that pressure is way way way too low. From what i recall it needs to be 800kpa-1200kpa when compressor is engaged. i think 500kpa - 600kpa is the engagement pressure for 98's if i recall correctly.

[abscate]

Low / high ratio should be in range 5-6x in mild CT weather. That’s ratio with compressor engaged, not static pressure which is meaningless.