R129 air con problem

[Shadychris]

Your problem is likely with the RPM sensor on the compressor, or the wiring to/from it (devoid of any insulation?) The ecu sees no compressor rotation and disconnects the compressor for safety.

Thanks for that - I did wonder about that myself. However I now have the self diagnosis N22 AC controller info and have worked through that. Other than an error 70 for the aux pump 'open circuit' which persisted a couple of times but has now cleared after fiddling with the connector, I have no DTC codes stored. Im not getting an error 73 for AC pump signal.
Wiring harnesses look to have been replaced with insulation in good condition.
Next step today is to knock up a blink code reader and see what error codes I have on pin 16 of the 38pin BM module..

 

[mattkh]

...... but has now cleared after fiddling with the connector,

I would still look at the inside of this connector. Clean with acetone, and tighten the crocodile jaws

 

[Shadychris]

I would still look at the inside of this connector. Clean with acetone, and tighten the crocodile jaws

Thanks I did that already! I'm sure that's OK now and I havent had any error codes returned back to the N22 self diagnostics stored codes.
I have now tried a code blink read on the 38 pin socket. Seems I was wrong about Pin 16 being AC related for my particular MY I dont even have an active PIN 16.
However I pulled all the codes from all my 'active pins' (there were quite a few!) and interestingly socket 8 which relates to the Base module on my MY had a code 7 indicating Poly v-belt slipping.... Wondering now if maybe that would cause the AC clutch cut-out circuit to throw a hissy fit. Ran out of time today but will recheck tomorrow to see if that DTC error has returned..

 

[Shadychris]

Think I've finally got to the bottom of this. I had stupidly thought the AC monoblock was the auxiliuary pump. I now realise that the aux pump is buried deep underneath the AC monoblock. The error 70 for the aux pump does keep returning, and checking continuity of the pump with my multimeter (on the correct wires this time) does show that the pump coil is indeed open circuit... Looks to be a nightmare to get to, so I wont be in a rush to get that done. I'm also fairly sure that will not impact on operation of the AC pump clutch.
@alexanderfoti seems to have hit the nail on the head. Pins 2 & 3 on the AC pump which connect back to the speed sensor are open circuit and I'm getting zero AC voltage on those pins with the pump spinning by means of 'hot wiring the clutch to 12V dc

 

[alexanderfoti]

Think I've finally got to the bottom of this. I had stupidly thought the AC monoblock was the auxiliuary pump. I now realise that the aux pump is buried deep underneath the AC monoblock. The error 70 for the aux pump does keep returning, and checking continuity of the pump with my multimeter (on the correct wires this time) does show that the pump coil is indeed open circuit... Looks to be a nightmare to get to, so I wont be in a rush to get that done. I'm also fairly sure that will not impact on operation of the AC pump clutch.
@alexanderfoti seems to have hit the nail on the head. Pins 2 & 3 on the AC pump which connect back to the speed sensor are open circuit and I'm getting zero AC voltage on those pins with the pump spinning by means of 'hot wiring the clutch to 12V dc

You will probably find the cables are destroyed, but if not its the sensor itself. I think the pump needs to come off to replace the sensor but don't quote me on it. Alternatively you could fabricate an rpm signal from an optical or hall sensor pickup on the face of the pulley. It would be a bit if fab work but may be less work than dropping the compressor?

 

[Shadychris]

You will probably find the cables are destroyed, but if not its the sensor itself. I think the pump needs to come off to replace the sensor but don't quote me on it. Alternatively you could fabricate an rpm signal from an optical or hall sensor pickup on the face of the pulley. It would be a bit if fab work but may be less work than dropping the compressor?

The wires look good and actually the bracket assemply and cable al llook quite shiny and new so maybe they were replaced when the AC pump was overhauled, and I'm just unlucky that its failed quickly. There's zero access so it would be a pump out job, and I see that I am likely to pay nearly as much for the speed sensor alone as for a complete new pump with the sensor included....
Great idea about rigging something up on the front face of the pulley to generate a signal, would not be hard to do and quite a cheap way out as no need to evacuate the system and drop the pump - which looks like a pig of a job anyway...
I guess if I'm not too bothered about the belt protection side of things I could just steal a signal from an engine speed sensor somewhere - I guess there must be at least one for the rev counter alone...?

 

[alexanderfoti]

The wires look good and actually the bracket assemply and cable al llook quite shiny and new so maybe they were replaced when the AC pump was overhauled, and I'm just unlucky that its failed quickly. There's zero access so it would be a pump out job, and I see that I am likely to pay nearly as much for the speed sensor alone as for a complete new pump with the sensor included....
Great idea about rigging something up on the front face of the pulley to generate a signal, would not be hard to do and quite a cheap way out as no need to evacuate the system and drop the pump - which looks like a pig of a job anyway...
I guess if I'm not too bothered about the belt protection side of things I could just steal a signal from an engine speed sensor somewhere - I guess there must be at least one for the rev counter alone...?

Yes exactly, you can do but I'm sure the ac compressor probably spins faster than the engine as its smaller than the crank pulley so would need to take that into account. All OK a kick in the bum, especially as you have changed the pump recently.