P38A 2.5 D aircon issue -> no code in EAS unlock, but get the service book

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svenology

svenology

Member
Posts
30
Location
Ventimiglia, Italy - Border to France
I have a strange issue....

My p38a has a pressurized AC, it works, when I manually trigger the compressor... so I know I have a non leaking circuit, I have a good compressor... BUT
when the climate control is on auto with AC enabled, I can hear the AC compressor kick in once... and then after a first cycle, it stops for the rest of the time the ignition is on/engine running and I get the dreaded book symbol in my HVAC module.
Having used the RSW EAS unlock to read faults... NO FAULTS occur.
The only fault I have is AC unrelated and shows some issue with stuck flap on left motor when auto tuning...
That fault is displayed, and no book symbol....
but the book symbol apparently has no code.... and aircon clearly not working.

Restart the car, with AC in off mode... no book symbol. For days, weeks, months.
turn on AC, you can hear the compressor engaging... wait... takes about 3-5 minutes.... compressor turns off... book symbol. never comes back on after that.

Trinary switch!? or what do the experts think???
 
svenology said:
I have a strange issue....

My p38a has a pressurized AC, it works, when I manually trigger the compressor... so I know I have a non leaking circuit, I have a good compressor... BUT
when the climate control is on auto with AC enabled, I can hear the AC compressor kick in once... and then after a first cycle, it stops for the rest of the time the ignition is on/engine running and I get the dreaded book symbol in my HVAC module.
Having used the RSW EAS unlock to read faults... NO FAULTS occur.
The only fault I have is AC unrelated and shows some issue with stuck flap on left motor when auto tuning...
That fault is displayed, and no book symbol....
but the book symbol apparently has no code.... and aircon clearly not working.

Restart the car, with AC in off mode... no book symbol. For days, weeks, months.
turn on AC, you can hear the compressor engaging... wait... takes about 3-5 minutes.... compressor turns off... book symbol. never comes back on after that.

Trinary switch!? or what do the experts think???
Click to expand...
EAS Unlock for HEVAC faults? Run the aircon in manual mode and see if it works There are sensors involved that will stop the aircon working, they will show on diagnostics and will produce the book symbol if faulty. It is unlikely to be the trinary switch. A stuck blend flap should produce the book symbol unless it's transient. Excess gas pressure will also stop the aircon from working but does not produce the book symbol.
 
kermit_rr said:
The book symbol is only triggered by a blend/distribution motor and unrelated to any ac issues
Click to expand...
If this is indeed true and I get NO book symbol, when AC operation is OFF, but I get a book symbol after about 3-5 minutes of AC operation, (based on engine sound, I'd say it is about the time when the AC compressor disengages after its first on cycle)
I get it every time, I try to use the AC. It clears after an ignition cycle...
I don't get it at all if the AC is off.

I had blend flap motor issues on my old P38... but that caused the service book symbol to show and it stayed until codes were cleared... i.e. forever... also they didn't affect the AC... it ran just fine.
 
Datatek said:
EAS Unlock for HEVAC faults? Run the aircon in manual mode and see if it works There are sensors involved that will stop the aircon working, they will show on diagnostics and will produce the book symbol if faulty. It is unlikely to be the trinary switch. A stuck blend flap should produce the book symbol unless it's transient. Excess gas pressure will also stop the aircon from working but does not produce the book symbol.
Click to expand...
yes. the EAS unlock has HEVAC connectivity and can read, clear faults and also has all kinds of calibration and test functions for the blower motors and blend flaps...
I had hoped it would give me the code for why the book symbol appears when the AC is engaged... but nada... no code for that.
And I am sure it's the AC circuit causing it... as it won't appear at all when the AC is in off mode... and it must be something pretty grave, if it prevents the compressor from running. hence my guess now is that it is one of the pressure switches...
 
I have seen similar. If the blend flap happens to be close enough (and the HEVAC does not do calibration on that drive), then my book symbol sometimes stays off. If I then adjust temperature, the stuck motor brings up the book.

Most likely nothing to do with the compressor, but check the actual pressure both static & when compressor runs. Maybe it's tripping something ?
 
RangeRoller dt said:
Have you check the belt is not slipping (simple things 1st) or AC clutch ?
Click to expand...
+1 on this. There must be some heating effect in the clutch coil, so if the gap is too large it migh not pull in properly after the first time ?

Gap should be 0.4 to 0.8mm.
 

Attachments

  • AC clutch repair.pdf
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pwood999 said:
+1 on this. There must be some heating effect in the clutch coil, so if the gap is too large it migh not pull in properly after the first time ?

Gap should be 0.4 to 0.8mm.
Click to expand...
Just to reiterate. My compressor clutch is fine. Using a jumper to engage the clutch manually gives me nice cold air.
So the system works in terms of charge and the compressor doing what it needs to do.
 
Has the car got the clutch relay, or the earlier version driven directly from the HEVAC ? If it's the early version, check what voltage the clutch is actually getting.

I had a problem on my 1998 where the clutch was getting intermittent. 12V directly via jumpers always engaged it, but the HEVAC could not always engage it, especially when when engine was warm. I found the gap on mine was a bit large (1.5mm), so sorted that & now it always engages.

Also check the footwell connectors C202, and the dual pressure switch connectors.

What is the system pressure ? Either too low or too high makes the pressure switch open-circuit, which disengages the clutch.
 
Datatek said:
You are effectively by-passing a gas pressure problem.
Have you tried running in manual mode?
Click to expand...
That’s why I am thinking dual pressure switch. I even have the part sitting on my desk… just have never pulled a bumper… and have no helper.
Anybody done a solo bumper removal?
Mine is pristine and color matched with the car. So don’t want to get it ruined…
On the plus side the entire mount and brackets don’t seem to have any rust. Car hasn’t been in salt, snow, off road.
AC acts the same for auto mode or manual mode when the AC is allowed. Ie button not lit…
After a few minutes on the first run… book icon appears. You can even tell it cooled a little briefly. Which you can also hear in the engine sound/rpm stabilization when the compressor kicks in first and then turns off.
 
svenology said:
That’s why I am thinking dual pressure switch. I even have the part sitting on my desk… just have never pulled a bumper… and have no helper.
Anybody done a solo bumper removal?
Mine is pristine and color matched with the car. So don’t want to get it ruined…
On the plus side the entire mount and brackets don’t seem to have any rust. Car hasn’t been in salt, snow, off road.
AC acts the same for auto mode or manual mode when the AC is allowed. Ie button not lit…
After a few minutes on the first run… book icon appears. You can even tell it cooled a little briefly. Which you can also hear in the engine sound/rpm stabilization when the compressor kicks in first and then turns off.
Click to expand...
Why change it without checking it first with a meter? I am never in favour of changing parts on spec, often it just introduces new uncertainties. Bumper off single handed is not difficult, putting it back is a bit harder.
 
I waited for my eas cable from RSW hoping it would allow me to get a code… but no dice. The only code in the HEVAC which doesn’t even clear is left blend flap failed auto calibration… but it seems to work just fine when I play through the settings. Also pretty sure the clearing of the code is not happening because it is still there minutes later… also that doesn’t cause the book to pop up…
I am all with you… but to check the switch is as complicated as replacing it in this case… so doing a check by inserting a new part is while expensive a valid check.
Not sure at this point what else besides that it even could be…
Unfortunately it seems the 2001 diesel has a lot of features that are not in rave.
Like clearly it uses the condenser fans for cooling when the engine coolant is above a certain temp… not just for AC…
 
There are no code for the dual-pressure switch. If the pressure is above 35psi it will be closed, so the HEVAC can engage the compressor. If the gas stays between 17psi & 305psi then it will remain closed & allow the HEVAC to control the compressor on-off as required. Note: the other half of the dual-pressure switch turns on the right condenser fan at full speed if the pressure goes over 305psi.

- Too much or too little gas will cause the compressor to cut out.
- 2001 model should have the extra relay, so the clutch gap is less critical, but still needs to be correct.
- Pressure switch connections do get corroded, so try cleaning them.

1756746989442.png
 
kermit_rr said:
The book comes on after a few mins. That sounds like it's coming the car and trying (but failing) to move the blend motors as a result
Click to expand...
Yes. But book only comes on when the ac is being tasked. Otherwise no. Also won’t stay once the ignition is cycled. Always same behavior.
Going cold to hot (ambient air) works without issues. So to my knowledge the blend motor uses the same position for full cold and outside air intake regardless.
Full hot and full cold settings seem to work just fine.
 
pwood999 said:
There are no code for the dual-pressure switch. If the pressure is above 35psi it will be closed, so the HEVAC can engage the compressor. If the gas stays between 17psi & 305psi then it will remain closed & allow the HEVAC to control the compressor on-off as required. Note: the other half of the dual-pressure switch turns on the right condenser fan at full speed if the pressure goes over 305psi.

- Too much or too little gas will cause the compressor to cut out.
- 2001 model should have the extra relay, so the clutch gap is less critical, but still needs to be correct.
- Pressure switch connections do get corroded, so try cleaning them.

View attachment 348970
Click to expand...
The not having any code is frustrating…
But as the dual pressure switch is the only other dependency of the compressor and I had the AC professionally evacuated and recharged, I don’t know where else to look. Who votes for just pulling the bumper and replacing the switch.
Seems that more than a couple times that is to blame for non functioning ACs
The clutch shouldn’t be at fault if I can jumper it and it works fine… right!?
 
svenology said:
I waited for my eas cable from RSW hoping it would allow me to get a code… but no dice. The only code in the HEVAC which doesn’t even clear is left blend flap failed auto calibration… but it seems to work just fine when I play through the settings. Also pretty sure the clearing of the code is not happening because it is still there minutes later… also that doesn’t cause the book to pop up…
I am all with you… but to check the switch is as complicated as replacing it in this case… so doing a check by inserting a new part is while expensive a valid check.
Not sure at this point what else besides that it even could be…
Unfortunately it seems the 2001 diesel has a lot of features that are not in rave.
Like clearly it uses the condenser fans for cooling when the engine coolant is above a certain temp… not just for AC…
Click to expand...
The condensor fans are only used in an overheat situation and come on too late to be any use. I actually use them in place of the viscous fan.
Your HEVAC could be faulty, the aircon relay could be faulty, the fuse box could be faulty and as previously mentioned, sensors or excess gas pressure. Very few aircon related problems bring up the book symbol, so it may be that your sticky blend flap is in fact the cause. Have you tried manual mode?
 
Front bumpers tend to be okay, rear one often comes off and won’t go back on. Some manage fine you could be a lucky one. Best have a good mooch underneath with the EAS right up before tempting fate if you feel there may be crumbliness in there, although I don’t think it’s a bumper off job
 
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