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

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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...

Often had the bumper off on my own.

Undo the clips at either side, undo the two bolts, push down in the centre to disengage it and then pull it towards you and it just slides out. Get ready at the end as it comes free and the ends drop towards the floor.
 
okay... latest update.
Code in the HEVAC (says left blend motor failed auto tune) doesn't clear with my RSW EASv4 tool... no way it resets faster than 30 seconds it takes to reread codes again.
but the book doesn't relate to it...
book is off if AC is not in use...
when the AC is allowed to run, the following behavior shows...
AC clutch engages... runs for a few seconds (5-45, longer at first, then less long) and you can feel the tubes getting cool...
then it disengages... it does that about 2-3 times, and then the book shows in the AC.
I don't think it engages again after the book shows up (3-5 minutes after initial start)
Turn of the car... turn on again... i can repeat this 100 times. Exact same behavior.

So been thinking about this... and sure... the HEVAC sends on and off for the AC... but in the end, an AC needs to cycle... and I think the cycle is done by the dual pressure switch... once pressure is reached, it turns off the compressor, then turns back on once the pressure is below threshold again etc...
seems that there is no code for whatever is not working in the HEVAC... it just shows the book.... but according to all articles on blend flap motors etc... for those issues the book stays and needs to be cleared for new ones to even work...

So who thinks the issue is not the dual pressure switch??
 
Grrrrrr said:
Often had the bumper off on my own.

Undo the clips at either side, undo the two bolts, push down in the centre to disengage it and then pull it towards you and it just slides out. Get ready at the end as it comes free and the ends drop towards the floor.
Click to expand...
i know this sounds super "princess"... but my bumper is gloss color matched to the body paint...
In your estimation, if I put down a blanket... what's the chance I still get it damaged due to warp, falling etc??

also... off is one question like @Datatek said... but back on all alone??
 
RangeRoller dt said:
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
Click to expand...
honestly i think the car has basically no rust for a a Range Rover... the clips all seem visible and moveable.
If the bumper wasn't painted I would have already taken it off a long time ago... but this one is pristine and has a clear coat etc... so my worry is getting it all ruined when I fumble it off myself... or latest when I try to put it on.
When the weather allows... maybe I just will attempt it next week...
 
svenology said:
okay... latest update.
Code in the HEVAC (says left blend motor failed auto tune) doesn't clear with my RSW EASv4 tool... no way it resets faster than 30 seconds it takes to reread codes again.
but the book doesn't relate to it...
book is off if AC is not in use...
when the AC is allowed to run, the following behavior shows...
AC clutch engages... runs for a few seconds (5-45, longer at first, then less long) and you can feel the tubes getting cool...
then it disengages... it does that about 2-3 times, and then the book shows in the AC.
I don't think it engages again after the book shows up (3-5 minutes after initial start)
Turn of the car... turn on again... i can repeat this 100 times. Exact same behavior.

So been thinking about this... and sure... the HEVAC sends on and off for the AC... but in the end, an AC needs to cycle... and I think the cycle is done by the dual pressure switch... once pressure is reached, it turns off the compressor, then turns back on once the pressure is below threshold again etc...
seems that there is no code for whatever is not working in the HEVAC... it just shows the book.... but according to all articles on blend flap motors etc... for those issues the book stays and needs to be cleared for new ones to even work...

So who thinks the issue is not the dual pressure switch??
Click to expand...
I don't think it's the tri state switch, more likely the sensor on the evaporator pipe. I'm also inclined to suspect your diagnostics as a sticking blend flap will always produce the book symbol eventually. A defective tristate switch will not show the book symbol, it has no connection to the HEVAC. The other possibility as previously mentioned is the output drive transistor in the HEVAC.
 
If the fault is present the the fault can't be cleared. The AC side doesn't produce the book symbol.
You need to fix the blend motor problem before you go any further

Edit: my car never had working AC. I did have a blend motor issue but once i replaced it, the symbol was gone. Didn't matter whether i had the ac button on it off
 
+1 on first job is to sort the LH Blend motor. Remeber the book symbol comes on for any faults within the HEVAC system.

Probably worth getting a set of AC gauges & check the pressures. Even if you never re-gas yourself, at least you then know if the system is within range. Plenty on Amazon around £30-£50.

If I remember correctly, the static pressure with engine off should be about 60-70psi depending on ambient temp. Then with engine on & compressor engaged the low side should drop << 50psi, and high side rise to above 150psi.

Very unlikely the system is reaching the max pressure on the switch, but a good check is if the fans are actually running full speed ?

If you raise the suspension to max, you can reach the dual-pressure switch from underneath. Easier with bumper off, but do the checks first. Do NOT bypass it & run the AC without the protection.

1756925884786.png


R134a Temp-Pressure Chart.jpg
 
kermit_rr said:
If the fault is present the the fault can't be cleared. The AC side doesn't produce the book symbol.
You need to fix the blend motor problem before you go any further

Edit: my car never had working AC. I did have a blend motor issue but once i replaced it, the symbol was gone. Didn't matter whether i had the ac button on it off
Click to expand...
I have had 3 failed motors on my last RR and other than the adjustments not working or the left and the right getting different temps of air, when they should be the same, the AC always worked... i lived in California... and a no AC car is as bad as a failed engine car there!
 
pwood999 said:
+1 on first job is to sort the LH Blend motor. Remeber the book symbol comes on for any faults within the HEVAC system.

Probably worth getting a set of AC gauges & check the pressures. Even if you never re-gas yourself, at least you then know if the system is within range. Plenty on Amazon around £30-£50.

If I remember correctly, the static pressure with engine off should be about 60-70psi depending on ambient temp. Then with engine on & compressor engaged the low side should drop << 50psi, and high side rise to above 150psi.

Very unlikely the system is reaching the max pressure on the switch, but a good check is if the fans are actually running full speed ?

If you raise the suspension to max, you can reach the dual-pressure switch from underneath. Easier with bumper off, but do the checks first. Do NOT bypass it & run the AC without the protection.

View attachment 349108

View attachment 349112
Click to expand...
Car has been recharged at a professional shop and the pressure was all good.. also no leaks... but also there... the AC did not cycle... so the million dollar question... who determines the cycling and via what sensors?
Clearly the HVAC codes for the fail don't exist.
My blend motor fault might be bogus. As the blending from hot to cold works just fine... and the auto tune of the doors happens the more rare the older the car. Forcing a calibration also does not throw the book symbol.
 
svenology said:
i know this sounds super "princess"... but my bumper is gloss color matched to the body paint...
In your estimation, if I put down a blanket... what's the chance I still get it damaged due to warp, falling etc??

also... off is one question like @Datatek said... but back on all alone??
Click to expand...

I've had mine on and off alone quite a few times. Tricky part getting it back on is getting the sides to slot back into place. Mine is just black plastic coated and not colour coded though. Don't know if yours is any more fragile but mine's pretty robust.
 
svenology said:
Car has been recharged at a professional shop and the pressure was all good.. also no leaks... but also there... the AC did not cycle... so the million dollar question... who determines the cycling and via what sensors?
Clearly the HVAC codes for the fail don't exist.
My blend motor fault might be bogus. As the blending from hot to cold works just fine... and the auto tune of the doors happens the more rare the older the car. Forcing a calibration also does not throw the book symbol.
Click to expand...
See post #25. If your car is post 1998, It is possible to remove the aircon relay and jumper two pins which will eliminate the relay wiring and tri state switch from the problem. Diagnostics should show the state of the evap sensor, if that is faulty it will shut the aircon down. And as I said before, a faulty drive transistor will shut the aircon down, it's a current sensing device, under or over current will cause a shut down with the book symbol. If you don't have circuit diagrams, I'll post the relay info this evening when I fire up my office computer
 
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1756973947206.png

Remove relay #3 and jumper pins 30 & 5 on the drawing. The relay pin numbers will not actually be the same but a DVM will tell you which pins are which.
If the aircon runs with the jumper, you are left with 3 main possibilities, faulty relay, evap sensor or the HEVAC drive transistor, assuming the connectors are OK.
 
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Datatek said:
View attachment 349132
Remove relay #3 and jumper pins 30 & 5 on the drawing. The relay pin numbers will not actually be the same but a DVM will tell you which pins are which.
If the aircon runs with the jumper, you are left with 3 main possibilities, faulty relay, evap sensor or the HEVAC drive transistor, assuming the connectors are OK.
Click to expand...
I will give that a look. what I am missing in this diagram is the second switch that is for the fans... or is this a newer version, which would explain why my fans switch on when the engine gets very hot.... which seems to not be mentioned anywhere else for the the diesel models...
 
svenology said:
I will give that a look. what I am missing in this diagram is the second switch that is for the fans... or is this a newer version, which would explain why my fans switch on when the engine gets very hot.... which seems to not be mentioned anywhere else for the the diesel models...
Click to expand...

Later models have an extra temperature sensor on the head which turns on the aircon fans just after the head has cooked itself. Earlier models just cooked themselves.

As mentioned above there are a dizzying array of HEVAC units. Marty did a good write up on here somewhere. The biggest change was that earlier models drove directly whereas later models just switched an extra relay. A replacement unit can do both but it has to have the right part number.
 
Grrrrrr said:
Later models have an extra temperature sensor on the head which turns on the aircon fans just after the head has cooked itself. Earlier models just cooked themselves.

As mentioned above there are a dizzying array of HEVAC units. Marty did a good write up on here somewhere. The biggest change was that earlier models drove directly whereas later models just switched an extra relay. A replacement unit can do both but it has to have the right part number.
Click to expand...
+1 on this. Remember a prev owner may have swapped the controller due to LCD issues, etc. Simply the early HEVAC will engage the clutch once, but not see enough current, so it thinks to clutch is faulty & disengages again until the next time the HEVAC is powered on.
 
svenology said:
I will give that a look. what I am missing in this diagram is the second switch that is for the fans... or is this a newer version, which would explain why my fans switch on when the engine gets very hot.... which seems to not be mentioned anywhere else for the the diesel models...
Click to expand...
svenology said:
I will give that a look. what I am missing in this diagram is the second switch that is for the fans... or is this a newer version, which would explain why my fans switch on when the engine gets very hot.... which seems to not be mentioned anywhere else for the the diesel models...
Click to expand...
Second switch for the fans? There is no second switch, see diagram below. In addition there is an engine overheat sensor that will switch the fans on, the engine should never get hot enough to trigger that sensor.
1756979978603.png
 
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