Air Con not working (I know why) but Lexia not reading Air Con ECU

[Rhothgar]

I am so glad that I bookmarked this and this post.

Sadly, I cannot recall bookmarking it so I have been going through a ground up diagnosis of why my air con ECU will not communicate with the Lexia and I've learned some interesting things along the way.

Chris' marked up coloured diagrams are superb and very useful including the 'oddball' situation markup which I have. Basically, my system has NO refrigerant in it at the moment and it's probably been dry for a number of years. Just hope I am not going to have to replace the seals on the pipework! I'd bet that will be a PITA of a job.

My air con clutch is also not actuating. I have powered it directly but there is no click. I've bridged the trinary switch both pins 1 and 2 and, 3 and 4 so I am thinking that is why I achieved the 'oddball' situation of the right hand fan going at full tilt whilst the left looked all forlorn. The bearings, as I posted some years ago, are pretty much short on the right hand fan.

I stripped the aircon ECU down yesterday and there is corrosion on parts of the board which I have now rectified. I noticed a very dark capacitor coming off pin 4 which is the communications pin so even swapped that out.

Prior to swapping the capacitor out, I managed to get a fault come up for the air con BUT in the engine ECU. P1110 Temporary Air conditioning cut-off circuit. Short circuit to earth or open circuit..

Does anyone know how to decipher this please:-

Coolant temperature 51degC
Engine speed 803rpm
Actual flow 10 mm3/stroke (This is measured injector flow)
Deceleration control (Inactive - button) ???
clutch inactive (air con clutch presumably)
Driver's request inactive (Button on dash?)
Main brake inactive ???
Ignition positive active
Maximum transitional output 31 mm3/stroke ????

Obviously, I had been running the engine when this fault occurred.

I plan on getting the system pressure checked and regassed this week so maybe it will start throwing faults then.

Naturally, I wouldn't want to bridge the trinary wires if the clutch was working as it could probably damage the compressor. I am not sure if I heeded warning previously though about being careful to power the compressor with the correct polarity but would giving 12V to the earth side of a diode actually BLOW the compressor diode. It's there to stop current flowing the wrong way, is it not?

I note all the forum posts about the peculiar steps people have taken in the past to get the air con ECU to read. It might be that a particular signal relay in my Lexia is duff and not allowing the data to flow. That would be my guess.

[mickthemaverick]

Glad to see you've sussed the linking Roger!!