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Member
Joined: Dec 22 2016
Posts: 284

Hi folks,

So I've got a rangey in just now which has faults on two out of three blend motors. Simplest solution is to throw a brand new set of genuine motors at it, or so I hoped.

I've bought them, hooked them up, and after resetting the faults... I get faults still. O.o

Far as I can see electrically, the motors are all fine, as are the potentiometers. So I dug a bit further into the pinouts in RAVE, the nanocom HEVAC pdf, and testing voltages with a multimeter. Doing this I discovered an oddity. Two of the three blend motors use red/black as their negative potentiometer voltage reference, as you'd expect based on RAVE. But the right hand potentiometer is mis-wired in all the harnesses I've looked at.

Pin 1 is supposed to be the right hand potentiometer positive voltage reference, and pin 5 the negative. Based on the multimeter, RAVE is correct. But the nanocom manual has them the opposite way round, which you could easily write off as a mistake, but the wires themselves are backwards in the harnesses I've seen.

Can anyone that's got a harness handy have a look and see what colour wires go into pins 1 and 5?

To save you digging in RAVE to figure out which pins that is, if you look at the connector, pin 3 is empty, so pin one is two to the left of the empty slot, and pin five two to the right. Both are on the outside edge of the HEVAC ECU.

Thanks!

Member
Joined: Aug 07 2019
Posts: 41

no1 is grey and no5 red black strip
no7 white no9 brown no10 black
the pins can be removed with the smallest flat jewellers screw driver
PS it may have been removed to replace the blend motor at some stage instead of replacing them all

Member
Joined: Dec 22 2016
Posts: 284

Yeah I could understand if it were on one of the two old harnesses I have here, but both of them and the brand new genuine set have the same issue.

So yours are correct.. Curious.

Member
Joined: Dec 22 2016
Posts: 284

Sorry, I should've waited to post this until today when I was a bit more with it.

Pin 1 should be negative (ie. red/black), and pin 5 should be grey (positive), so your's is miswired too.

Member
Joined: Dec 22 2016
Posts: 284

More testing later, my best guess is that there was a mistake in production, so they modified the hevac firmware to invert the potentiometer readings rather than have to go back and fix all the harnesses. :)

So yeah keep pin 1 as grey and pin 5 as red/black.

Sadly my nanocom still won't tell me what the faults are (shows blank screens), but I can guess...

The distribution motor moves a bit one way, then the other, then gives up moving until you power off/on again, at which point it does the same thing. Start up current on the motor appears to never go over 50mA, and more usually is around 7 or 8mA once running.

I'll retest the potentiometer readings. Again. Yay.

Member
Joined: Aug 07 2019
Posts: 41

they wouldn't be wired back to front because they are opposite and work back to front.
how tight are the distribution flaps and other flaps , if you have to put physical effort into moving them they are probably to tight should move with the flick of a finger.

Member
Joined: Dec 22 2016
Posts: 284

I'd expect the left and right hand flaps to be free, but the distribution flaps move three sets of flaps via gears, so those are never going to be movable with a finger flick.

Also the fact that the motor current is down at < 10mA implies it's not exactly being worked hard.
Think I'll check an unloaded motor to see what current it draws too for comparison.

Member
Joined: Dec 30 2015
Posts: 1099

The distribution flaps should be moveable with very little force - the later heater boxes are obviously a bit different to the early ones, as you can move the distribution flaps on one of them with your little finger (yes, I was surprised too the first time!)

One thing with the HEVAC... it will ONLY actually clear the faults with the ignition cycled - so if you go in an clear the faults, it will say it's cleared them, but it won't actually erase them from memory until you power off and back on again.

Are the flaps/motors at one of the end points currently or set to middle? If they are set to middle, then it sounds like something else weird is going on. If they are at one of the end stops, then I'd reset them to middle (can move the motors with a 9V battery) as it could be that at the end point it's showing out of range on the HEVAC due to calibration.

Other things it could be... it could be the wiring being backwards on the connector. I fit a new set of blend motors to my RR not so long ago - I'll try and see if I got a picture during reassembly which shows the connector/wiring colours.

Another possible option is that it could be the driver IC in the HEVAC controller that has failed. It's a fairly rare occurrence, but it does happen. They are replaceable. One of the symptoms of them having failing is a constant error in the HEVAC with it telling that it is short to positive and possibly negative at the same time.

First thing to check though is how tight the distribution flaps are. Also, one of the sets of flaps can become disconnected from the drive, as the drive rod works it's way out the other side of the heater box (can only see it with maybe the glove box out, but definitely with passenger air bag removed.

There are possibly a few other places to check aswell - I'll have a think... I've done heater boxes/blend motors on 8 or 9 P38's now, and reconditioned more HEVAC controllers than I can remember - so I'll rack my brains and see if I can think of anything else..

oohhh, I've actually got a HEVAC on the bench that I need to finish testing (I have a P38 heater box with blend motors I use) - so I'll try and get a picture of the blend motor connector. I don't think anything is messed up in the firmware of the HEVAC controller - as I've tested everything from the early AWR1011/1012 through to the later JFC102540/102550 controllers with the same set of blend motors, and they've all reported proper values, and calibrated properly. I'll see how my set of blend motor wiring matches up with the RAVE wiring too.

Member
Joined: Dec 22 2016
Posts: 284

I've pulled the hevac again and will sort the flaps out; they're not welded but there's room for improvement and the current from the motor is higher than I'm happy with, so that might help. The errors, when it was throwing them, were potentiometer faults rather than motor shorts, but with HEVAC, nothing is necessarily as it seems. :)

Member
Joined: Dec 30 2015
Posts: 1099

I've just been testing the units I have here and looked at the wiring on my test set of blend motors, and also another set which I have kicking about.

Pin 1 here on both sets is Grey, and pin 5 is Red/Black, which is correct as per the RAVE ETM - right the way from the 1995 version through to the 1999 onwards version - so my guess is the Nanocom manual is incorrect, or they must have done a firmware change before production of the HEVACs - one of the units I've serviced was a REALLY old AWR1011 unit, dated 1994 and the software version showing in the SETTINGS on Nanocom was 0.... which I've never seen before - I've seen 4, 5, 6, 7 but nothing really lower than that (though most of the units I do are AWR5051 and newer).

But it sounds like your blend motors themselves are wired as per the manual and how they should be...

Member
Joined: Dec 22 2016
Posts: 284

Yup, they are wired 'correctly'. Took the HEVAC unit apart and cleaned up the flaps, lubed them and trimmed them slightly to reduce friction. Calibrated fine afterwards. Hey ho. :)

Member
Joined: Aug 07 2019
Posts: 41

when you say cleaned up the flaps do you mean you trimmed up the rubber edges around the flaps or modded the inside of the air box. the real issue is the box shrinks and the end float of the shafts dissapears this is where the problem is if the flaps are tight
ps when the lube dries it will fault again?

Member
Joined: Dec 22 2016
Posts: 284

mad-as wrote:

when you say cleaned up the flaps do you mean you trimmed up the rubber edges around the flaps or modded the inside of the air box. the real issue is the box shrinks and the end float of the shafts dissapears this is where the problem is if the flaps are tight
ps when the lube dries it will fault again?

I trimmed the edges where they were visibly adding excessive drag, and added more end float in places by sanding back the box. Lube is silicon based so shouldn't dry out in a hurry.

Member
Joined: Aug 07 2019
Posts: 41

did you remove the heater box from the vehicle , which flaps did you trim.

Member
Joined: Dec 22 2016
Posts: 284

Yes box out and completely disassembled. Checked each set for drag. It was the small set of flaps at the bottom of the box which were causing the majority of the drag.

If you have no air conditioning gas it's also worth pulling the box behind that out and dismantling/cleaning it. I cleaned a customers one recently which had enough leaf debris in it for a nest. Tried vacuuming it out with a long pick up tube without removal but it's nigh on impossible in situ to get much of it.

Member
Joined: Aug 07 2019
Posts: 41

ok that sounds good that you did remove the box , i had a vision of you trimming the flaps on the top off the box and not actually removing it . if yo have good end float and all is free it should be good. how did you go with the white gear on the side as they can be tight too

Member
Joined: Dec 22 2016
Posts: 284

Seemed alright to me.