Clearing HEVAC faults

[zzsteve]

Having trouble clearing HEVAC fault (RH blend motor feedback potentiometer error) after replacing and checking the pot in the blend motor. I 'clear faults' in the Nanocom and cycle ignition, but fault is still there when I read again and checkbook comes up almost immediately on the display. Confusing because the blend motor doesn't even get nudged to check the potentiometer anyway.
I'd like to recalibrate blend and distribution motors, but this doesn't happen either despite progress bar displayed on the Nanocom.
I'd be grateful for any tips or advice.
TIA

Steve
'95 HSE

[prelude]

I ran into this problem with a set of blend motors myself. It was quite a b*tch to get that to work. I have 3 pairs of motors and 2 hevac units and between the lot I got it to work out. I first connected a pair of know good motors to the hevac unit and send them to the middle position. I switched these to the other hevac unit to clear the error (and keep it cleared) then I started messing around with the other motors on the spare hevac to get them to behave :( Once I had the set I wanted to use in a state where they were NOT on their ends (some I had to manually move with a power supply) I cleared faults in the spare hevac and positioned the motors in a known good position. I then proceeded to mounting the motors so that they could not accidentally overrun (they have slightly less movement when mounted) and connected them to the hevac unit I intended to use. Once "booted" I could run the calibration test and voila! no errors and the motors have been working since.

I'm pretty sure some steps I have taken are not needed but that is what I did to get it working. ymmv.

Good luck!

-P

[zzsteve]

Thanks!
So, my best option might be to manually drive all three motors to midpoints and try again.
Steve

[prelude]

Steve,

Yes and make sure they are mounted so they can't overrun.

Cheers,
-P

[vk2loz]

hi all just to add to the confusion ,,
my motors are reverced to the nanocom ,,
If i cycle the left (on the nanocom ) the right blend motor runs if i do the right the left one moves ,,
I talked to Lee at labtronics he says this is a comon fault ,,, and some replace the wrong side ,,,
lee has a fix give him a yell ,,,

[zzsteve]

Still going on this one, but thought I'd share some success, observations and remaining problems.
Thought I was stumped by the potentiometer feedback error on RH blend motor, but checked the replacement pot and found that the new one has the central slot at 90 degrees to the factory one at the same resistance. It is the PIHER PT 15 NV, but there is a N and a G version with the wiper position 90 degrees different. Be careful of what you exactly order - or recieve if attempting this repair. This explains why lining up the arrows on the gears could never work for me. Additionally, when I measured the replacement pot it was quite nonlinear i.e. first 1kohm is all done in a few degrees and the last 1-2kohm is quite spread out. It is claimed to be a linear pot though!. Quick clean of the old one and it was back in and set it all up for midrange on pot, mid position on RH blend flap and flat part of the engagement dog aligned with the long edge of the motor.
OK, blend fault gone!
Now, the fault 19 'left recirc. motor short circuit to positive 12 V' comes up. I can drive the motor open and closed with +/- 6 volts on the plug out of the back of the HEVAC unit, but the HEVAC thinks it is 'shorting to +12 v' which is nonsensical as the motor is isolated from earth and floats with a differential input depending on the direction it is being driven. Thought it might really mean an over-current situation, so measured the drive current in both directions with 6V at 30mA and the RH one was 37mA! The LH recirc flap is definitely opening and closing and I've had the blower assembly out, cleaned and replaced.
The bigger picture I want to fix when all this HEVAC humbuggery is sorted, is the initial cold A/C disappearing after a few minutes (usuallly from a cold start). Compressor engages, but it is cold on the big tube for a few minutes, then it all goes away! I don't see how it could be related, but open to any suggestions!
TIA
Steve
'95 HSE

[prelude]

Steve, I feel your pain mate ;)

I have been mucking around with the hevac systems for days on end, god help me if it fails again I'll replace it with a nice touchscreen and a raspi or arduino... [bighmmm]

Anyway, the short is error is probably correct. I have been hunting around for a similar error for hours on end until I was so fed up I drove over to my mate and claimed his digital scope for a few hours (much to his amusement he saw me coming in, no words were exchanged, I ripped the scope from the desk and started working.. he knew when to shut up :P).

As it turns out, and the same goes for the position pots, the HEVAC measures instant value's as fast as the electronics can handle. A normal digital multi-meter and even an analog one shows nothing, but a worn brush that has dislodged or a bit of dirt that causes even a millisecond of short, things that burn away immediately without fuss and large currents trigger the HEVAC instantly. The momentum of the motor has long since passed it's bad point but it's already too late.

So, even when measuring to check you cannot be certain. I would try a different motor on that spot, hell, even swap the left and right servo's and see what it does. Good chance the error will have swapped sides as well. If not, you may have been lucky that the change of scenery motivated the servo to work for a while without the hevac complaining!

Regarding the AC. If the big tube is cold for a while and then heats up, I would suspect the clutch to have disengaged as well? If not, that would be weird. The aircon system works on pressure difference, ie. you compress a gas in the condensor at the front, remove the generated heat that comes with it and slowly release the gas into the vaporizer in the car, which cools it down and in turn cools your car etc. etc. If the ac get's cold for a moment, the compressor continues to run (clutch engaged) but the tubes warm up, IMO that means that there is not enough gas or backpressure in the system after a short while.

Anyway, this is becoming very speculative until you can provide more details :)

Cheers!
-P

[zzsteve]

Thanks Mate!
I considered your thoughts on the recirculation motor triggering the HEVAC on any small current glitch and just replaced both with 330 ohm resistors spliced into the cut wires out of the plug. I drove each recirc. flap to closed as I just want optimal cooling here and I can use the windows for fresh air anyway. At least they work. Applying 6V (negative to WR and WG wires will drive them closed)
So, the recirc. fault on HEVAC now goes - to be replaced with - RH blend motor stall fault. No more time for this, so made sure it was stalled at the cold end and patched it all back together as I need the vehicle for some real jobs now.
Maybe I'll track down another blend motor and check it on the bench to within an inch of its life next time.
Not sure where to go with the anaemic AC. I have regassed after replacing tx valve and new dryer. Maybe probe the pressure switches to see what they reveal.

135531
Cheers,
Steve

[prelude]

Glad you got a workaround for it :) The resistor will indeed fool the HEVAC unit for now.

Keep us posted if you ever get back to working on the real problem though!

Regarding the AC, some more random thoughts: What can happen is that the condensor in the front of the vehicle gets old and clogged on the inside. The system cannot get rid of the heat efficiently and the pressure buildup is too high and the system stops working. The problem may also reside with the regulator valve blok. That's the part that sits between the vaporizer and the tubes and can be accessed from the engine bay. I suspect my AC has a problem there but I have yet to find a new replacement part for that.

Anyway, with the AC gas prices having skyrocketed since oktober down here (6x over) due to the eu not wanting to use that gas anymore testing around with the AC to see what fixes it has become a hugely expensive undertaking, especially since the system holds 1250 grams of the stuff... Myself I am considering replacing all the easy to replace and suspect parts right away since it will probably be cheaper to do that then to gas/regas the system over and over :(

Cheers!
-P

[zzsteve]

Glad you got a workaround for it :) The resistor will indeed fool the HEVAC unit for now.

The problem may also reside with the regulator valve blok. That's the part that sits between the vaporizer and the tubes and can be accessed from the engine bay. I suspect my AC has a problem there but I have yet to find a new replacement part for that.
Cheers!
-P
Yep, that's the thermoexpansion valve or TX valve, which I have replaced. I found an aftermarket one from Ashdown Ingram (local auto parts supplier).
Because I occasionally get suitably cold output from the compressor, I'm thinking there is a compressor clutch drive problem due to faulty sensor or trinary switch, so I'll work my way through those next. I have had the A/C clutch relay modification, but I wonder if the gap might still be out of spec. too.
Cheers,
Steve

[HowdyP38]

I ran into this problem with a set of blend motors myself. It was quite a b*tch to get that to work. I have 3 pairs of motors and 2 hevac units and between the lot I got it to work out. I first connected a pair of know good motors to the hevac unit and send them to the middle position. I switched these to the other hevac unit to clear the error (and keep it cleared) then I started messing around with the other motors on the spare hevac to get them to behave :( Once I had the set I wanted to use in a state where they were NOT on their ends (some I had to manually move with a power supply) I cleared faults in the spare hevac and positioned the motors in a known good position. I then proceeded to mounting the motors so that they could not accidentally overrun (they have slightly less movement when mounted) and connected them to the hevac unit I intended to use. Once "booted" I could run the calibration test and voila! no errors and the motors have been working since.

I'm pretty sure some steps I have taken are not needed but that is what I did to get it working. ymmv.

Good luck!

-P
Thanks Prelude & Steve. I'm glad I read this because I have been stuffing around with the distribution servo trying to get rid of the feedback circuit and potentiometer faults even though everything measured OK. Once I replaced the potentiometer and positioned the gear correctly so that the potentiometer gear was exactly mid stroke while the center of the wide part of the big gear made contact with the matching gear (mine was also an ebay pot which works perfectly but the slot is out by roughly 90 deg) I must have tried 10 times to get it to work. My mistake was that I either tested it or cycled the ignition prior to installing the servo which drove it to one end every time. So as you mentioned, all the travel isn't used when installed so the secret is to position the servo in the mid position before installing it, then clear the fault and calibrate the servos. How good does it feel to have no book there, or in my case coat hanger sticking out of the dash operating the distribution flap. [bigsmile]

[zzsteve]

Thanks Prelude & Steve. I'm glad I read this because I have been stuffing around with the distribution servo trying to get rid of the feedback circuit and potentiometer faults even though everything measured OK. Once I replaced the potentiometer and positioned the gear correctly so that the potentiometer gear was exactly mid stroke while the center of the wide part of the big gear made contact with the matching gear (mine was also an ebay pot which works perfectly but the slot is out by roughly 90 deg) I must have tried 10 times to get it to work. My mistake was that I either tested it or cycled the ignition prior to installing the servo which drove it to one end every time. So as you mentioned, all the travel isn't used when installed so the secret is to position the servo in the mid position before installing it, then clear the fault and calibrate the servos. How good does it feel to have no book there, or in my case coat hanger sticking out of the dash operating the distribution flap. [bigsmile]

Thanks for the story. Mine is all back together, but the control of distribution and blend motors by a custom micro has stalled while I replaced the radiator and the brake switch and work on the trailer...
I've put it all back with conventional RC servos on brackets and will start faffing about with driving them soon. I've also put PWM drivers on the blower fans as the recirc and blower fan would also throw HEVAC errors. This bit goes well, and it is tempting to just gang the drive pots together and put them on a panel in place of HEVAC. BTW, I learned that only having one blower working is a big problem, as it acts as a huge leak for the working fan.
Cheers,
Steve

[HowdyP38]

Man you must be an Electrical Engineer, you lost me at RC Servos.[bigwhistle] I wish I understood all that, I just fumble my way through this stuff so I'm really appreciative of the posts on this forum. The first thing I think of with all these issues (and I have had pretty well all the usual P38 issues which mysteriously appeared the day after I brought it home[bigsad]) is bugger this just re-engineer it but most issues are electrical which is my weakest area so i'm stuck with standard controls. Easy to say while it all works at the moment. I didn't throw the coat hanger out. Yep the blowers need to both operate - what if you block off the faulty motor's pollen filter would that give you flow until you get it going?

[p38arover]

When you reassembled the blend motors, did you align the arrows?

You can see them here: Blend Motor Diagnosis and Replacement (http://www.rangerovers.net/repairdetails/blendmotor.html)

[TheTree]

I too have experienced mayhem with the recirculation motors !

I replaced my passenger side one (which at the very least requires the dash pad to be loosened so you can get the blower out) and didn't pay a lot of attention to it's position [bighmmm]

So i continued to get the chequebook symbol although the flap was moving through it's full range.

So when I had to replace the aircon evaporator (which was not only leaking but badly clogged) and had the dash out, I tried again with the recirc motor.

I use a 9v battery to drive it through it's range to determine both end positions, I then positioned it in the middle of it's range and also positioned the flap in the middle and refitted the motor.

Now the chequebook symbol comes and goes with the weather !!! The flap opens and closes properly so I am suspecting some kind of overrun error but I can live with it for now

I have now replaced every bit of my air con system, both the condenser and evaporator were in bad shape and i replaced the pressure switches and dryer when I did the condensor

zzsteve's issue of it going on and off may have to do with one or both of the pressure switches in the system

Steve

[zzsteve]

Man you must be an Electrical Engineer, you lost me at RC Servos.[bigwhistle]
Yes,actually.
The RC servos are just high-torque radio controlled model servos with ball bearings. Great price/performance ratio compared to a set of blend motors! The ally box is one of the 30 amp PWM controlled drivers for a blower motor. ~$12 on eBay.The knob on the front is what I plan to mount on a panel where the HEVAC control/display now lives (temporarily). I had temperamental recirc motors too, so have locked them in the recirc position and drive the blower motors directly now. I am gradually de-Valeoing the system and will continue until I have chequebook-free zone. Couple of pics attached to show the servo mounting scheme on the heater box and a blower controller.
Cheers,
Steve

[zzsteve]

I too have experienced mayhem with the recirculation motors !
zzsteve's issue of it going on and off may have to do with one or both of the pressure switches in the system

Steve
Not in the end. With poor airflow over the evaporator, the sensor was dropping the AC grant signal before any cool air reached the customer. Leaky compressor didn't help, AND, don't think those early Commodore/Falcon Sanden compressors are a fit to the P38 GEMS. They are close, but a cm or two off on the mounting holes. I found a good P38 compressor in a wreck.
Cheers,
Steve

[TheTree]

Not in the end. With poor airflow over the evaporator, the sensor was dropping the AC grant signal before any cool air reached the customer. Leaky compressor didn't help, AND, don't think those early Commodore/Falcon Sanden compressors are a fit to the P38 GEMS. They are close, but a cm or two off on the mounting holes. I found a good P38 compressor in a wreck.
Cheers,
Steve

Yeah I thought my compressor may be the problem at one point so I did some research, my air-con guy says there are lots of fakes around so be careful what you buy !

This is what my evaporator looked like when I got it out !

Steve140160

[zzsteve]

Yuk.

I guess a replacement evaporator would be worth as much as my entire vehicle...

S

[TheTree]

Yuk.

I guess a replacement evaporator would be worth as much as my entire vehicle...

S

The ones with the tri state valve included were not cheap, I got an allmakes one out of the US for around $200 landed with no valve since I had already replaced mine

Steve

[HowdyP38]

When you reassembled the blend motors, did you align the arrows?

You can see them here: Blend Motor Diagnosis and Replacement (http://www.rangerovers.net/repairdetails/blendmotor.html)
In the end, no. I did at first before realizing the slots in new potentiometers were about 90 deg out so I set the midrange of the potentiometer travel to the mid range of the wider part of the other gear.

[HowdyP38]

I too have experienced mayhem with the recirculation motors !


Now the chequebook symbol comes and goes with the weather !!! The flap opens and closes properly so I am suspecting some kind of overrun error but I can live with it for now


Steve

Steve, maybe try getting hold of a Nanocom and calibrate the servos. Then they shouldn't over-run I would have thought.

[HowdyP38]

Yes,actually.
The RC servos are just high-torque radio controlled model servos with ball bearings. Great price/performance ratio compared to a set of blend motors! The ally box is one of the 30 amp PWM controlled drivers for a blower motor. ~$12 on eBay.The knob on the front is what I plan to mount on a panel where the HEVAC control/display now lives (temporarily). I had temperamental recirc motors too, so have locked them in the recirc position and drive the blower motors directly now. I am gradually de-Valeoing the system and will continue until I have chequebook-free zone. Couple of pics attached to show the servo mounting scheme on the heater box and a blower controller.
Cheers,
Steve

Haha Good guess. That PWM unit is cool, wish I found that when I was dodgeying up the boost controller on my race car. Also I wonder if it would drive an extra injector for a turbo P38? Those servos are a neat fit too.

[TheTree]

Steve, maybe try getting hold of a Nanocom and calibrate the servos. Then they shouldn't over-run I would have thought.

I own a nanocom and tried calibrating the servos but it did not seem to make any difference :(

Thanks anyway mate !

Steve

[zzsteve]

I own a nanocom and tried calibrating the servos but it did not seem to make any difference :(

Thanks anyway mate !

Steve

There is a 'calibration' cycle of distribution and blend motors on every power-up. The HEVAC looks for the end stop positions by looking for a current peak in each drive direction. This sets its limits in firmware. It maybe why electrically noisy pots and/or motors just won't calibrate even if they test OK on the bench. A Nanocom calibration might seek these limits too, but more importantly I think it maps the distribution motor positions with respect to the limit positions so that airflow to face, feet and screen etc... is correct.
Watch those replacement pots. There are two models, different by one letter in the part no. and the only difference is - the slot is 90 degrees away.
HTH
cheers,
Steve

[TheTree]

There is a 'calibration' cycle of distribution and blend motors on every power-up. The HEVAC looks for the end stop positions by looking for a current peak in each drive direction. This sets its limits in firmware. It maybe why electrically noisy pots and/or motors just won't calibrate even if they test OK on the bench. A Nanocom calibration might seek these limits too, but more importantly I think it maps the distribution motor positions with respect to the limit positions so that airflow to face, feet and screen etc... is correct.
Watch those replacement pots. There are two models, different by one letter in the part no. and the only difference is - the slot is 90 degrees away.
HTH
cheers,
Steve

Hi Mate

These are the Reticulation/Recirculation motors which are attached the the blowers and control the fresh air flaps under the pollen filters. There is no mention of these specifically in the nanocom but one would imagine they are calibrated as well when the other motors are

They are also a different motor, 2 wire instead of 3 wire.

Given the extreme difficulty in accessing these bastards, I am happy to live with the occasional cheque book on the display !

Steve

[TheTree]

I just noticed that the gears for these motors are now available [bigrolf]

HVAC Air Conditioning Recirculation Servo Gear Motor For Range Rover P38 SAAB | eBay (https://www.ebay.com.au/itm/323267645096)

Steve