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Thread: Clearing HEVAC faults

  1. #1
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
    Posts
    200

    Clearing HEVAC faults

    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

  2. #2
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    258
    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

  3. #3
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
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    Thanks!
    So, my best option might be to manually drive all three motors to midpoints and try again.
    Steve

  4. #4
    Join Date
    Jan 2016
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    Netherlands
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    Steve,

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

    Cheers,
    -P

  5. #5
    Join Date
    Oct 2017
    Location
    nowra
    Posts
    61

    on mine the right is the left ??

    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 ,,,

  6. #6
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
    Posts
    200

    an update, but not quite there yet...

    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

  7. #7
    Join Date
    Jan 2016
    Location
    Netherlands
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    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...

    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
    Last edited by p38arover; 14th May 2018 at 09:54 AM. Reason: Removed foul language dodge

  8. #8
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
    Posts
    200
    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.

    IMG_1764.jpg
    Cheers,
    Steve

  9. #9
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    Jan 2016
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    Netherlands
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    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

  10. #10
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
    Posts
    200
    Quote Originally Posted by prelude View Post
    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

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