I'm a bit stumped... Book error came up on RR no 2, and as I had a couple of spare 2nd hand blend motors, which tested fine I thought I'd open her up on the RHS and replace both motors. Distribution flaps were a bit tight and i loosened them off with the self tapper in the middle. After a bit of swapping ( i have two hevac's, repinned the connector, swapped motors over) I have a Distribution motor that powers up on ignition II and seemingly a functioning LH and RH blend motor and i can watch the blend %age (on Nano) go up and down all day long - although not the distribution motor. But...i keep getting one error (ie only one at a time) in Faults...it is variously RH blend motor open circuit, RH blend potentiometer circuit has failed, RH blower is open circuit. I would merrily go and buy some new blend motors if i believed that was the error, but it would be great if Nano could make up its mind. it might even make sense if it said that it was the distribution motor...

Has anyone developed any relevant expertise in the interpretation of the nano?

I normally use the Diagnostic function and move them from 0 to 100%. You can hear them operating and see what the feedback pot is reporting. It will often go to 105% (which is a good trick if you can do it) but you'll be able to see if you are getting full travel and the correct feedback.

Yes - that's the bit I can do "all day long" - all blend flaps working fine...but if the RH potentiometer is not the problem (even if the Fault screen says it is) then why the book symbol?

The distribution motor powers up/ adjusts on ignition, but then pressing the various buttons on the HEVAC doesn't elicit a response...so the one message I could understand is "distribution potentiometer not working" - but nano has never said that so then it makes me think "programming glitch", but that way madness lies

Think I solved the problem, but not entirely sure why... RR no 2 came with a rather sorry looking HEVAC unit in the boot... looking at it there were traces of a genuine double sided gasket on the front of the unit - so I realised that it was probably the original ECU. I tested it and found that the distribution switches were not working - which was presumably why the PO changed it out. Opened up the unit - cleaned off the contacts...installed it, and book symbol gone... The original was 101890, whereas the fitted one was 102550... whether it really has to do with the model number, still not sure, but I had a second 102550 and that was not co-operating either, so seems fairly likely.

I suspect my HEVAC connector socket contacts have the usual "gone loose with age" problem. Mine mainly affects the passenger vents so not often an issue for my6 side of the car !!

I also get the book symbol, which usually clears after cleaning the 16-pin connector. Still trying to figure out how to pull the socket contacts from the housing to tighten them. Ideally I would prefer to replace the connector, but cannot find one, except on 2nd hand motors.

You mean you want the black 16 pin male socket for the blend motors? With the female pins...its an Amp econoseal J series 40 16 way (not type II) ...they're there if you look hard

https://www.ebay.co.uk/itm/123377070040?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=DzEeh3cqQ76&sssrc=2349624&ssuid=&var=&widget_ver=artemis&media=COPY

Thanks. Ordered one with contacts. Will update when fitted & see if the issues gets resolved.

romanrob wrote:

Think I solved the problem, but not entirely sure why... RR no 2 came with a rather sorry looking HEVAC unit in the boot... looking at it there were traces of a genuine double sided gasket on the front of the unit - so I realised that it was probably the original ECU. I tested it and found that the distribution switches were not working - which was presumably why the PO changed it out. Opened up the unit - cleaned off the contacts...installed it, and book symbol gone... The original was 101890, whereas the fitted one was 102550... whether it really has to do with the model number, still not sure, but I had a second 102550 and that was not co-operating either, so seems fairly likely.

Actually, sor anyone following, seems it's best to avoid the 101890 unit. It doesn't store the external temp and starts every journey at snowflake, so no a/c until you have hit c 35 mph for 5 mins... I had to switch back to a 102550 again. this is was the subject of a service bulletin apparently, though i didn't track down the actual doc