Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Yes, another P38 HEVAC question

  1. #1
    4X4V8 Guest

    Yes, another P38 HEVAC question

    I have been holding off asking anything on this because of the truck load of online HEVAC info.
    However I haven't found a simple troubleshooting guide. So plenty of guides for specific problems, but now I'm a bit confused on what to do with my HEVAC issues. Any help or links appreciated. I have been Googling and reading for a while!

    - Since buying the P38, book symbol has appeared on HEVAC. A/c works and all air direction flaps appeared to work.

    - My new RSWV4 told me I had a right blend motor out of range fault. I also discovered one cool evening that heated air would not distribute to the right footwell. RSWV4 could not seem to clear this fault, but on occasion the book would dispappear on start up, to soon again reappear.

    - Yesterday car was parked in hot sun 2hr for first time since I have had it. A few moments after starting up, a loud clicking could be heard coming from the upper dash area; maybe 6 to 10 clicks. In my mind it sounded like a plastic component binding and releasing. I knew it was one of the HEVAC motors and/or door shafts. Soon the book symbol arrived, as did hot air only from driver's side vents, regardless of temp position selected. Pass side vents running correct air temp.

    -Checked RSWV4 when home and it said 'distribution motor self-test failure' or similar. Couldn't clear it. Interesting to note that the previous fault, the right hand blend motor fault, was now not mentioned by the RSWV4.

    So far: The system is noting an air distribution problem. The noise I heard from the upper dash seems to confirm. Yet the actual fault appears to be one of incorrect air blending, not air distribution. Am I missing something?

    Right. I thought for starters I should pull HEVAC display unit, unplug it and put 9v across motors at plug. Try to put them to centre positions (how do you do this without seeing motors? You can only see them by pulling cluster and/or dash apart --- so you use an ammeter to check that motors are at mid-range values?

    Then I'd put it back together, use the RSWV4 to calibrate motors (BUT don't the motors self-calibrate on each and every start up anyway, therefore absolutely no point calibrating on diagnostic tool?) and see if book symbol reappears.

    If it does reappear and I have the most troubling problem (hot air cooking me, the driver) then I would disassemble the dash, check all 3 motors for gear, pot and motor brush issues and the blend doors for binding. While I'm there, replace the heater o-rings with Viton rubber o-rings and clean ducting, replace foam seals etc.

    Regardless of whether the book symbol re-appears I should probably do the above anyway. The problem is only going to come back.

    Is it better to try to recondition or revive the original motors rather than fit the aftermarket replacements, which I got the feeling when reading up on them are a bit cheap and nasty?

  2. #2
    4X4V8 Guest
    Tried the 9v direct to motors test. Left blend and distribution motors sound like they are moving freely. The right blend motor however reaches a point where you can hear the motor loading up as if meeting resistance then something clicks and then it carries on as normal to the end of travel. That’s in one direction. When powering it in the opposite direction it doesn’t load up (until reaching the end of travel). Despite that, the fault appearing on rswv4 is ‘distribution door motor stalled during self calibration’.

    I couldn't get my digital Ohm meter to work while doing this test for some reason. I understand an analogue meter is better to test the consistancy(?) of the movement but couldn't find mine.

    Either I've got pull out the dash and check eveything or just try to remove the rhight blend motor. Despite what RSWV4 is telling me, it appears to be the rh blend motor. One check I might try is to pull the cluster shroud and try to see what the distribution and rh blend motors do when trying to self calibrate.

    My gut feeling is that I have a binding problem with the air blend flap and I am going to have to take the dash apart so I can free it and also see if the motor has been damaged. Fun, not!

  3. #3
    Join Date
    Nov 2015
    Location
    Black Rock
    Posts
    997
    Total Downloaded
    0
    First up, it has been years since I replaced blend motors in a P38, so please don't take what I say as gospel. Also, I think I only ever did two (a friend's and mine) and assisted in a third. Others here will have better knowledge (and memories!).
    You don't have to pull the whole dash apart, but you do have to be prepared to cut and refix the plastic air ducts in order to easily access the right hand motor. This sounds drastic, but is really quite easy as you can tape them back together with any decent fabric tape so they're as good as new.
    From memory, the left hand motor is easily accessed by removing the passenger airbag. I forget about the central one, but I think it's behind the radio somewhere and is also straight forward to access.
    The blend motors (which are all identical) come wired together in a set of three. But you often only need one of them and anyway it can be easier to cut the wires and re-solder them as replacing the loom probably requires removing even more of the dash.
    But the good news is that once you can physically see them, you can easily check to see if they're working by running the HEVAC system through it's range. You will readily see which motor is not moving it's lever through the full range.
    I have one new blend motor for sale in the engine ancillary section.
    2013 D4 expedition equipped
    1966 Army workshop trailer
    (previously SII 2.25 swb, SIII 2.25 swb & lwb, P38 Vogue, 1993 LSE 3.9V8 then HS2.8)

  4. #4
    4X4V8 Guest
    Thanks mate, might take you up on that motor. Just need to see exactly what the problem is. I’ll see if I can attach some pics of where I’m up to. As far as I can see, access is all via the instrument cluster. Someone has been in here before; there are drill holes through the duct at approx where the right blend motor screws are. The upper join of the duct has been taped up, but to me it looks like a factory join point. I just have to figure out where to cut the duct soI I can get to the motor.

  5. #5
    4X4V8 Guest

  6. #6
    4X4V8 Guest
    FInally got the right blend motor out. It looks just about new to me compared to what I've seen online. One corner of a tooth on the large centre wheel might be a little mishapen but that's it.

    I don't know what to do next except put it back and try powering it again to see if it catches. Put a torx socket into the belnd door shaft and it seemed to turn okay... not sure.

    IMG_4579.jpg

  7. #7
    Join Date
    Nov 2015
    Location
    Black Rock
    Posts
    997
    Total Downloaded
    0
    Try manually moving the arm (that the blend motor is meant to be attached to). It should move freely for it's full articulation. Then power up the blend motor before putting it back to make sure it operates properly. Then make sure that you reconnect it correctly and power it again to make sure it operates the arm at full travel.
    Then check the other motors.
    2013 D4 expedition equipped
    1966 Army workshop trailer
    (previously SII 2.25 swb, SIII 2.25 swb & lwb, P38 Vogue, 1993 LSE 3.9V8 then HS2.8)

  8. #8
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    880
    Total Downloaded
    0
    If memory serves with an am-meter you should not see more than 500ma. I believe the HEVAC unit sees it as an error if the current becomes any larger than that, even for an instant. a digital meter is usually to slow to notice, analog ones might even be. It will throw an error and stop trying most of the times. If everything seems to move smoothly it could be the pot (variable resistor) in the housing. Again, even a value that is out of whack for a fraction of a second will throw them off. It could very well be that the noise you hear is not the actual problem but the pot is. Try measuring with an analog ohm meter and move through the range and see if the needle goes up and down without a hitch.

    Personally, I understand the easy way round to get to the blend motors but I never liked cutting through those ducts. They always become a sticky-tape mess and airflow is compromised eventually. So, I have taken the dash out several times already

    Good job on your P38 btw, give 'er the TLC she deserves mate!

    -P

  9. #9
    4X4V8 Guest
    Quote Originally Posted by prelude View Post
    Personally, I understand the easy way round to get to the blend motors but I never liked cutting through those ducts. They always become a sticky-tape mess and airflow is compromised eventually. So, I have taken the dash out several times already

    -P
    You know it was a tough call yesterday, whther to keep going and pull the whole dash. My garage is not very wide and I hadn't positioned the car well enough if I was to try to remove the dash (though the left front door). I ended up just using the holes already drilled though the duct for the rear screw. I didn't have to cut anything, but it did take me a long time to get to the forward attachment screw. Had to use a screwdriver bit on a 6mm(?) spanner.

    I thought my father gave me his old-school analogue ammeter. I will try to find it and see what readings I get.

  10. #10
    4X4V8 Guest
    Righto. Found the problem(s).

    I hadn't noticed it yesterday, but you can see in the pic I posted of the open motor assy that the gear on the left has about 4 stripped teeth. This I suspected when testing the removed motor (just hanging on its cable, but closed up) with a 9v battery at pins 9 & 10. There was a clearly audible click at about half way along its travel.

    When I split the box again (I stopped the motor test just at the point where it began to bind, about 1/2 way) the gears kind of popped out of place. As I tried to put it all back, I noticed the smaller double gear's teeth were all chewed up (where it takes drive from the worm drive on the motor).

    What caused this, in what appears to be a nearly new blend motor assy? Yep, a binding blend door. I hadn't noticed yesterday, but of course you don't need to stick a torx head socket or similar into the blend flap drive to test its operation. There's a small lever above that's attached to the shaft, presumably for lower spec models with manual HEVAC controls. By moving the flap by hand with this lever, I could feel a slight sticking point at about half way along the flap's rotation.

    So where from here is the question. I need to unstick the blend flap and replace the stripped motor gears at a minimum.
    First option is try to fix this without removing the dash.

    Can you insert a screw between the flap casing at the upper centre stack to relieve the pressure on a sticking right blend flap?

    Can you buy blend motor gears seperately?
    If yes to both, this is the quick and easy solution... but I suspect this isn't going to happen


    Other alternative is to reposition the car so that I can open the left front door enough (narrow-ish garage space) to remove the dash pad and fix the flaps and more easily replace the motor. I'm not sure if it's a good idea to start the car with the inst cluster removed but I suppose it'll only take a few sec to plug it in.

    I was hoping to use the car in the next few days, after which it can have a rest for a few weeks. Somehow I see a quick button-up job happening, with the blend motor unattached and a piece of wire attached so I can manually move the blend door. Then I can start pulling it all apart at my leisure in a few days.

    I still haven't touched the distribution door, which according to the RSWV4 is the problem (interesting it did mention the rh blend motor problem earlier on, but now that fault has disappeared to be replaced by the dist door fault). I'll need to take a look at the dist door as well, as I suspect that is binding too.

Page 1 of 2 12 LastLast

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!