P38 HEVAC

Before I start, I should say that this is my first post and although I’ve done lots of research, I’m sure I’ll put my foot in it somehow oh, and sorry for the long post!!

Ok, so I’ve done what you’re not supposed to do and bought a P38 with faults and no service history!! It was cheap, and the engine and box are good, so everything else is easy right?!

I’ve got the book symbol, and so far I’ve found at least 3 faults. The LH blower isn’t working due to a burnt out relay 7 (swapped it with relay 6 and fault switched sides) so I’ve ordered a new 40a relay to hopefully deal with the current better.

the recirc flaps aren’t working. The LH is closed and RH open/removed (I cant see it). I’m a bit stuck with this one. Tbh, I’m not fussed about recirc, so is there a way to force the flap open and frigging the electrics to fool the unit that the servo’s are working? If not, is it a case if removing the blower to access the flap, or does the dash really have to come out??

lastly (so far) the air con condenser is pretty badly damaged at the bottom, and what I think is the dryer canister next to it is badly corroded, so I think it may have lost its gas (does that cause the book symbol?)

I think the blend and distribution motors are working, and the RH fan spins up nicely, so that’s something at least!!

I have a big list of things to go through, but I have to say, there is something very appealing about these old trucks

oh, it’s a 2000 4.6 Vogue

If the relay is burnt, what is the state of the fuse box? Burnt fuse boxes are common.
If there is a blend motor missing, you will have the book symbol, everything needs to be present and working.
No gas does not give the book symbol on my MY2000 diesel.

Datatek said:

If the relay is burnt, what is the state of the fuse box? Burnt fuse boxes are common. You need to fit the correct relay as some have suppressor diodes fitted, without looking at RAVE, the workshop manual I don't know if the fan relay has one.
If there is a blend motor missing, you will have the book symbol, everything needs to be present and working.
No gas does not give the book symbol on my MY2000 diesel.

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You need to get a copy of RAVE and you will probably need diagnostics.

Datatek said:

If the relay is burnt, what is the state of the fuse box? Burnt fuse boxes are common.
If there is a blend motor missing, you will have the book symbol, everything needs to be present and working.
No gas does not give the book symbol on my MY2000 diesel.

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Correct lack of gas pressure shows no indication. Other than the compressor will not run.

Thanks for the replies. So for the moment I can ignore the air con until I get rid of the book symbol
I’ve got an online copy of Rave, but it only seems to pint at the location of the servos, rather than the correct orientation of the fresh air/recirc flaps. When you remove the pollen filter covers, you can see the LH flap is in what looks like the down position. I can’t see one on the RH at all, which to me means it’s either raised too high to see (if that’s possible) or it’s broken off/been removed

Diagnostics are well needed, but I don’t fancy spending the circa £300 on a nanocom or whatever, unless I can get some cheap software for a laptop?

On the plus side, I fitted the relay today and both fans work great. I haven’t removed the fuse box yet, but if it goes again, I will do, so thanks for that tip

Once this is sorted I can get onto fixing the washer pumps, FM reception, headlining, brakes, the transmission/steering fluid leak, service the engine, fit a new rear bumper, add the 12s electrics for caravan, and then...‍

Thanks again

robster_1981 said:

Thanks for the replies. So for the moment I can ignore the air con until I get rid of the book symbol
I’ve got an online copy of Rave, but it only seems to pint at the location of the servos, rather than the correct orientation of the fresh air/recirc flaps. When you remove the pollen filter covers, you can see the LH flap is in what looks like the down position. I can’t see one on the RH at all, which to me means it’s either raised too high to see (if that’s possible) or it’s broken off/been removed

Diagnostics are well needed, but I don’t fancy spending the circa £300 on a nanocom or whatever, unless I can get some cheap software for a laptop?

On the plus side, I fitted the relay today and both fans work great. I haven’t removed the fuse box yet, but if it goes again, I will do, so thanks for that tip

Once this is sorted I can get onto fixing the washer pumps, FM reception, headlining, brakes, the transmission/steering fluid leak, service the engine, fit a new rear bumper, add the 12s electrics for caravan, and then...‍

Thanks again

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Cheap diag is not available. EASunlock is available for little money but everything else needs dedicated diag. Like a Nanocom for instance. The other cheaper stuff falls well short of the usability of Nanocom.

wammers said:

Cheap diag is not available. EASunlock is available for little money but everything else needs dedicated diag. Like a Nanocom for instance. The other cheaper stuff falls well short of the usability of Nanocom.

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Yeah that’s what I’m thinking given the research I’ve done so far. I’m tempted to get a specialist to plug it in and get some pointers etc. In the past I’ve had BMW’s for a few years and got dealer software on my laptop and it has saved me a fortune over the years, and given that under the surface, this seems a solid vehicle, I might have to bite the bullet and invest!

One other question. When viewing the recirculating flaps through the pollen filter housing from outside the car, what should be visible? On the drivers side, I can see straight through to the fan and no flap is visible at all. On the passenger side, I can see a flap, which seems to be down and blocks the view of the fan.

I’m just trying to establish a baseline of what should be happening before I start shelling out cash.

robster_1981 said:

One other question. When viewing the recirculating flaps through the pollen filter housing from outside the car, what should be visible? On the drivers side, I can see straight through to the fan and no flap is visible at all. On the passenger side, I can see a flap, which seems to be down and blocks the view of the fan.

I’m just trying to establish a baseline of what should be happening before I start shelling out cash.

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Not at all sure you can see the recirculation flaps remembering the position of the actuators.
Not sure why you are bothering looking at the flaps, you need to get at the blend motors. You also need diagnostics to allow you to operate the blend motors.

Datatek said:

Not at all sure you can see the recirculation flaps remembering the position of the actuators.
Not sure why you are bothering looking at the flaps, you need to get at the blend motors. You also need diagnostics to allow you to operate the blend motors.

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I was just trying to establish how The system works before I start trying to diagnose anything. I appreciate that diagnostics might point me in the right direction, I’m a firm believer that you will be able to fix most things if you know what they should be doing. I’ve managed to find a photo online (haven’t got the link handy) of the flaps and I now know that the LH one is closed and the RH is open, so I suspect one of the motors has failed and or the gears have stripped.

I just need to suss out the pin out of the Hevac controller and I can apply 9v direct to the motors to prove which one works/doesn’t work.

Thanks for the advice

robster_1981 said:

I was just trying to establish how The system works before I start trying to diagnose anything. I appreciate that diagnostics might point me in the right direction, I’m a firm believer that you will be able to fix most things if you know what they should be doing. I’ve managed to find a photo online (haven’t got the link handy) of the flaps and I now know that the LH one is closed and the RH is open, so I suspect one of the motors has failed and or the gears have stripped.

I just need to suss out the pin out of the Hevac controller and I can apply 9v direct to the motors to prove which one works/doesn’t work.

Thanks for the advice

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You cannot see recirculation flaps without removing pollen filter housings.

wammers said:

You cannot see recirculation flaps without removing pollen filter housings.

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Ok, I’ll get on with removing those next time I get a few hours. Like I said, I can see one of the flaps through the slot with the pollen filter removed, but now I know that means it is closed, and the other one is open so cannot be seen.
I probably didn’t explain myself very well
Cheers

robster_1981 said:

Ok, I’ll get on with removing those next time I get a few hours. Like I said, I can see one of the flaps through the slot with the pollen filter removed, but now I know that means it is closed, and the other one is open so cannot be seen.
I probably didn’t explain myself very well
Cheers

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Sounds like you have a lot of work on your hands. Look for bad corroded connections first of all before stripping stuff down.

wammers said:

Sounds like you have a lot of work on your hands. Look for bad corroded connections first of all before stripping stuff down.

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Tell me about it! Most of it is general maintenance and niggly little jobs that I find quite rewarding, but this seems more frustrating than anything given how awkward it seems to get at!

I’ll come back with an update if/when I get it sorted

Bit of an update.
Managed to get an hour or two tinkering time today and I’ve got a good idea what’s going on.
I pulled the radio out, which gives access to the HEVAC looms. The 12 pin plug on the left nearest the front has the I/O for the recirculating flaps. IIRC pin 11/12 is the LH and 9/10 for RH. I used a drill battery and a couple of test leads to put power straight to the motors, and hey presto, both motors work and move the flaps perfectly. I got them both to the open position and plugged everything back in, turned the ignition on and the book symbol cleared!!!

Once I’d calmed down from my little dance, I tried everything and low and behold, when I pressed for AC, the book symbol re-appeared, and the LH flap had closed, but RH had not. I’m pretty sure they are ok, and just need re-calibrating??

On another note, while testing everything out, I noticed that the passenger side is stuck on hot, so blend motor I think? Also, the clutch on the AC compressor is not clicking in. I’m guessing that a new compressor is needed?

Thanks again for all the advice.

The ac compressor not kicking in could be low gas or a fault on the tri pressure switch,
some hevac`s need an extra wire to work the ac there was a post on what numbered hevacs work on what year car.
you could try 12v direct to the clutch feed and see if it works if it does then the fault is else where,

brianp38dse said:

The ac compressor not kicking in could be low gas or a fault on the tri pressure switch,
some hevac`s need an extra wire to work the ac there was a post on what numbered hevacs work on what year car.
you could try 12v direct to the clutch feed and see if it works if it does then the fault is else where,

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Nice tip, thanks I’ll try that!
I’ll have a search about that extra wire

robster_1981 said:

Bit of an update.
Managed to get an hour or two tinkering time today and I’ve got a good idea what’s going on.
I pulled the radio out, which gives access to the HEVAC looms. The 12 pin plug on the left nearest the front has the I/O for the recirculating flaps. IIRC pin 11/12 is the LH and 9/10 for RH. I used a drill battery and a couple of test leads to put power straight to the motors, and hey presto, both motors work and move the flaps perfectly. I got them both to the open position and plugged everything back in, turned the ignition on and the book symbol cleared!!!

Once I’d calmed down from my little dance, I tried everything and low and behold, when I pressed for AC, the book symbol re-appeared, and the LH flap had closed, but RH had not. I’m pretty sure they are ok, and just need re-calibrating??

On another note, while testing everything out, I noticed that the passenger side is stuck on hot, so blend motor I think? Also, the clutch on the AC compressor is not clicking in. I’m guessing that a new compressor is needed?

Thanks again for all the advice.

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Compressor failure is pretty rare, no gas, clutch failure, tri state switch etc are more likely.

Datatek said:

Compressor failure is pretty rare, no gas, clutch failure, tri state switch etc are more likely.

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Cheers
I can confirm that the clutch pulls in when 12v is applied direct, so I can discount that. I’m not certain exactly how the pressure switches work, but both of them are open circuit no matter what pins I go across. Not sure when they are supposed to switch. I am getting 12v at the switch wiring though, so I’m cautiously confident that the pressure switches are gone. The fans don’t come on either, which I understand should be on constant?
There is a fair amount of damage to the fins on the condenser and the drier unit looks very crusty, so I suspect it has no gas. I’m trying (very trying) my best to avoid just throwing new parts at it, when it could just be a faulty switch. Having said that, I’m prepared for the possibility of replacing parts if I need to. Everytime I look at the car, it grows on me! They are bloody awesome vehicles!!!

robster_1981 said:

Cheers
I can confirm that the clutch pulls in when 12v is applied direct, so I can discount that. I’m not certain exactly how the pressure switches work, but both of them are open circuit no matter what pins I go across. Not sure when they are supposed to switch. I am getting 12v at the switch wiring though, so I’m cautiously confident that the pressure switches are gone. The fans don’t come on either, which I understand should be on constant?
There is a fair amount of damage to the fins on the condenser and the drier unit looks very crusty, so I suspect it has no gas. I’m trying (very trying) my best to avoid just throwing new parts at it, when it could just be a faulty switch. Having said that, I’m prepared for the possibility of replacing parts if I need to. Everytime I look at the car, it grows on me! They are bloody awesome vehicles!!!

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The switches will not operate with no gas, they work on pressure, no gas = no pressure.
The fans only run on demand either at half speed or full speed, see RAVE for details