P38A HEVAC

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cornishboater

cornishboater

Well-Known Member
Posts
645
Location
Poole, Dorset
Hi all,
I am still fighting with my HEVAC unit but seemingly with no results. I am ordering a Nano Evo later today to sort some other issues, I think it is worth the investment now that I have decided to stick with the old girl.
In the mean time any ideas?
The book fault appears immediately when the key is turned on.
I have checked the following:
Blend flaps all move in manual mode (hot/cold, up/down and side to side) they all seem to move fairly quickly.
The in car sensor is spinning now (was full of dust bunnies)
Both fans spin up and run just fine
A/C is fully gassed and pumps nice cold air in when needed
Heat is also fine
Compressor clicks in and out as per other posts
New fuse box
New Pollen filters
The only thing I haven't confirmed is the action of the 2 recirc flaps, would these throw a fault if stuck?
Does the HEVAC unit reset itself each time it is switched off and on? I seem to remember I read somewhere that you had to disconnect it to clear the fault/s. Up to a bout 2 months ago I could drive for about 1hr before the book fault occurred, although this was intermittent to say the least! Now it is everytime the ignition is turned on.
Many thanks
 
cornishboater said:
Hi all,
I am still fighting with my HEVAC unit but seemingly with no results. I am ordering a Nano Evo later today to sort some other issues, I think it is worth the investment now that I have decided to stick with the old girl.
In the mean time any ideas?
The book fault appears immediately when the key is turned on.
I have checked the following:
Blend flaps all move in manual mode (hot/cold, up/down and side to side) they all seem to move fairly quickly.
The in car sensor is spinning now (was full of dust bunnies)
Both fans spin up and run just fine
A/C is fully gassed and pumps nice cold air in when needed
Heat is also fine
Compressor clicks in and out as per other posts
New fuse box
New Pollen filters
The only thing I haven't confirmed is the action of the 2 recirc flaps, would these throw a fault if stuck?
Does the HEVAC unit reset itself each time it is switched off and on? I seem to remember I read somewhere that you had to disconnect it to clear the fault/s. Up to a bout 2 months ago I could drive for about 1hr before the book fault occurred, although this was intermittent to say the least! Now it is everytime the ignition is turned on.
Many thanks
Click to expand...
Could be a sensor fault. Not sure but the book symbol does not seem to reset at every switch on on my project car. Not read of many problems with the recirculation blends sticking. The Nanocom will tell you what is going on.
 
It'll be the coolant temp sensor on the matrix, that was my fault anyway. Started intermittent then went permanent after about a year. New sensor and fine after that.
 
Hello mate,
That was what I thought, I replaced it with a brand new one a week ago and it is still the same unfortunately. Took me ages to track one down, rare as rocking horse poo now!
I guess the nano is my only chance of finding the issue, wasn’t wanting to fork out nigh on £500 but I guess I will have to!
 
Unfortunately without knowing what codes it's coming up with, you could be chasing yourself!

Yes, the recirc flaps will throw a fault, but I don't think this should happen right at startup - when I test HEVACs on the bench, I used to only have 1 recirc motor and unplug/replug between the 2 to make sure they were both being driven - but invariably, it wouldn't see stall current on one of the motors, and would flag it as a fault.
Also, yes, the book symbol will clear if the fault isn't present on the next power up.

I do think diagnostics is the best way forward - as you'll be able to see what the HEVAC thinks is the problem, aswell as live values for all the sensors etc.

Marty
 
Ta for the replies,
I have bitten the bullet and am now minus near on £500, but at least I can get some other bits sorted (maybe...)
So if anyone near Poole/Bournemouth needs codes read I'm your man (when I get it figured out that is) :)
 
cornishboater said:
Ta for the replies,
I have bitten the bullet and am now minus near on £500, but at least I can get some other bits sorted (maybe...)
So if anyone near Poole/Bournemouth needs codes read I'm your man (when I get it figured out that is) :)
Click to expand...
Pretty intuitive but take photos of any readings before you change anything, that way you can always get back to where you were.
 
cornishboater said:
Ta for the replies,
I have bitten the bullet and am now minus near on £500, but at least I can get some other bits sorted (maybe...)
So if anyone near Poole/Bournemouth needs codes read I'm your man (when I get it figured out that is) :)
Click to expand...

There's a guy near Southampton on here that bought one recently. Cannot remember his name now. Not far from Poole.
 
Further to my earlier posting, the rh temperature servo is indicated at fault, there is hot/cold to passenger and the flaps distribute to where they should, just only cold now to the driver. The question is, when looking at the RAVE docs it shows the rh temperature servo as the upper (Det 8) and the distribution servo as the lower one (Det 9)
I have looked on some of the LR forums and the various pics (not all) are showing them the other way around. Before I yank one or the other out can someone confirm which one is the RH temp motor pleeez.
Head lining being done this weekend, yippee, taking it to Jason down in yonder Taunton, got some good feedback on his work. I was going to go for black, but have decided to stick with the original (or "standard oatmeal" )
 
cornishboater said:
Further to my earlier posting, the rh temperature servo is indicated at fault, there is hot/cold to passenger and the flaps distribute to where they should, just only cold now to the driver. The question is, when looking at the RAVE docs it shows the rh temperature servo as the upper (Det 8) and the distribution servo as the lower one (Det 9)
I have looked on some of the LR forums and the various pics (not all) are showing them the other way around. Before I yank one or the other out can someone confirm which one is the RH temp motor pleeez.
Head lining being done this weekend, yippee, taking it to Jason down in yonder Taunton, got some good feedback on his work. I was going to go for black, but have decided to stick with the original (or "standard oatmeal" )
Click to expand...
You can confirm which is which with diagnostics by forcing the movement of the distribution flap. I think the one you want is the upper one and you will have to cut one of the heater distribution pipes to get at it. Re-fit with duct Tape.
 
Upper Servo is the distribution motor, the lower one on the RHS is the temperature blend.

Should have a wrap of blue tape on the cable to it, and it screws to a blue plastic standoff from the heater box itself. The distribution motor should have a grey wrap of tape around the cable, and slots into a big grey gear at the top of the heater box.

I find when doing them with the dash in (as Datatek mentions, you have to (CAREFULLY!**) cut the plastic duct to get to the screws to undo it, and you can get a bit more hand room by removing the metal LH instrument cluster bracket - it has 2 8mm nuts that bolt it to the top of the dash. Much more room to work with it removed.

**note... carefully cutting the duct... I've had to do a late night heater pipe replacement because someone was helping another owner out to replace the O-rings, and in cutting the duct, managed to hacksaw into the heater pipes, which then resulted in a flood of coolant when the owner next started the vehicle up!!
 
As Marty says upper motor on R/H side is distribution motor lower one is blend motor. Blend flaps don't seize distribution flaps certainly do.
 
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