Clearing HEVAC faults

Quote:

---

Originally Posted by 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

---

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]

Quote:

---

Originally Posted by HowdyP38

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

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?

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

You can see them here: Blend Motor Diagnosis and Replacement

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

Quote:

---

Originally Posted by HowdyP38

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

Quote:

---

Originally Posted by TheTree

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

Quote:

---

Originally Posted by zzsteve

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 !

SteveAttachment 140160

Yuk.

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

S

Quote:

---

Originally Posted by zzsteve

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