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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Sorry.... still working on mine. I just wanted to note on this thread that according to DengieBoy on the thread I link to below, the ambient air temperature sensor was located in the left pollen filter housing up to VIN381430 and behind the front grille from VIN381431 onwards.

Got mine working- kinda. Needed a new fusebox, compressor clutch overhaul (red flag), a whole new set of relays, overhauled blend motors (this bit was FUN) to get it this far. Now it has a totally dead HEVAC display and the temperatures fluctuate a little here and there but by and large it's working.

What's clear is that the HEVAC control unit in my car (AWR1012 manufactured in 1995) is NOT the one that shipped with the car. Being a 1997 (VIN VA356351), mine would have shipped with AWR5051 (thanks again marty_nz).

So..... if I have it figured right, the correct HEVAC control unit for my car is AWR5051, the ambient temperature sensor is in the pollen filter housing and needs to be moved AND I shouldn't have a relay in the RLY3 slot.

The killer is that today... there IS a relay in the RLY3 slot.

*facepalm*

I'm going to go looking for that ambient temperature sensor tomorrow...... and if it is indeed in the pollen filter housing, I'll move it and see how things go from there.

These cars just aren't for everybody........

http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/35421-ambient-temerature-sensor-where.html
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

I'm new to P38 ownership and I to have the cheque book symbol in the hevac display. All the airflow seems to be to the screen but I can control the temperature on both sides so I'm guessing the the door in the heater box is stuck or the motor is dead? I have read in detail all the threads regarding the blend motors and the heater box mod i.e. putting a aself tapper in the box. Question is where exactly does the self tapper need to go whats the most direct route to this I can't seem to find a link to this?

I also note that there are lots of problems with relays burning out in the hevac. I had a similar problem with my Porsche GTS I was advised by some yanks to buy a can of Deoxit you can get it from ebay but its expensive and worth every penny! Basicly its a spray you spray your relay and fuse contacts switches etc and it de corrodes and improves contact thus reducing resistance and heat build up. It really does work I had an electric window that was sluggish to close I sprayed the switch and now it will chop your arm off!

Nige
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Erm...... well from actually having had my dashboard and heater box completely apart in the course of this particular saga, it sounds like you have a stuck distributor servo (i.e. "blend motor") and it's one of the harder-to-reach ones on the right side as well.

As you know there are 3 "blend motors". One on either side controls a single flap which determines the mix of hot and cold air going to either side of the car according to what the driver and front passenger have selected as their preferred temperature.

The third one- on the right side, i.e. the hard-to-get-side on a RHD car- controls something like 5 flaps, all geared together which direct the air through whichever vent or combination of vents which have been selected. This "blend motor" (I like to call it a "distributor servo" which is a more functional description) is the upper of the two and drives a much heavier load as you can imagine, especially if the flaps are all fouled up with gunk and stuff, and is therefore more susceptible to damage. Looks like that's what you're dealing with.

I dunno about the self tapping screw solution but in your shoes I'd research how to go about pulling that servo out while leaving the other two in situ. Once removed, try actuating the flaps yourself by turning the white bit (see pic- which is what the output shaft of the servo engages to) by hand. It should be heavy but doable.... and smooth. If you feel like you have to force it or if the turning action isn't smooth then you have sticking or jammed distribution flaps.

A proper fix means removing the entire heater box, disassembling it, cleaning it all out, lubricating the pivots for each flap and reassembling the whole thing. O course, before you even got to this, the whole dashboard has to be removed, meaning an overall epic job.

Yeah- I went this route.

IF you don't mind not being able to direct the air and are happy with air just coming out from say the dash vents then a shortcut MAY be possible. IIRC (Jos and Marty please correct me if I'm wrong) you can access just that single distributor servo by removing the instrument pack. I think. It'll be a heck of a squeeze but I think, I think, I think you can just about remove the distributor servo from the heater box by working through the instrument pack port.

Remove the distributor servo from the heater box then with the blowers (at least) running, actuate the white bit by hand until air is coming out of your chosen vent(s). I don't think you need a screw at all- it's plenty stiff enough to stay put. Once that's done, tape or otherwise secure the freed distributor servo (now connected only by its wire) somewhere within the dash so it doesn't rattle about in there and reinstall the instrument pack. Job done. Air out from chosen vents, no screw but no way to redirect the air.

Might be worth popping the instrument pack out to see if you can get that distribution servo out of there.... I know you can SEE it once the instrument pack has been removed (and at least this is a fairly easy job- AND a great opportunity to change your instrument panel bulbs) but I've never tried removing it. If you CAN remove it then I think this bodge will be workable.


Only on RHD cars.

=)

Good luck!!


Screen Shot 2014-07-06 at 3.36.29 am.jpg
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

The self-tapping screw idea is that you undo some of the clips on the front of the heater box (visible when you take the fascia panel with the clock and switches off) and wedge a couple of self tappers in the seam up the middle of the heater box. This is supposed to wedge the 2 halves apart a bit and give the stuck flaps a bit more room to move smoothly.

The box I've had apart on the bench, I had to remove a fair bit of plastic from inside the box on one side to remedy the stuck flap - but it now works as it should.

The distribution motor is removable on a RHD vehicle by removing the instrument pack, yes. You have to loosen off the duct that goes past the distribution motor and RH blend motor so you can access the screws fully though. It is a pain to do sometimes, but it does beat taking the whole dash out!

The flaps indeed should be able to be moved by hand, with a little effort on the white/grey mechanism. Even on the box I've rebuilt it's not loose enough to do it with one little finger, but it does move smoothly and evenly across the range - and I tested it with a blend motor on the bench to make sure it wasn't going to struggle!

Marty
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Hi Marty..... and Jos... and anybody else who can help

I've just bought a new HEVAC control unit off ebay. This one is JFC102550 which going by your chart is the last incarnation of this piece of pain and is the correct fitment for P38s from VIN XA417600 onwards.

We also know that P38s before VIN XA411503 require that a relay be installed between the HEVAC ECU and the compressor clutch.

Mine's VIN VA356351, meaning I would have been effected had my car been a v8 derivative.... but it isn't, it's a diesel.

So far so good but then comes these three worrying bits of info:-
1) From the recall notice 0010 of 6/10/99 itself, only v8 derivatives require the Compressor Link Harness YMQ104590AA and extra relay. Mine's a diesel;
2) From http://www.stockholmviews.com/p38/index.html#hevac we know that fitting the newer HEVAC ECU type (which I presume my new JFC102250 is) which requires a relay into a car without a relay and expecting it to drive the clutch direct will kill the HEVAC ECU;
3) JFC012250 is a "direct replacement" and/or "supercedes" both AWR1012 (which I have now) and AWR5051 (which my car would have shipped with).

So..... the question is..... do I need to install this YMQ104590AA before I install my new HEVAC ECU?


In other words, does JFC102250 superceding AWR1020/5051 assume that YMQ104590AA has already been installed or does it have the same MOSFET output to allow it to drive the compressor clutch direct as AWR1012 and AWR5051 did?

It would seem that the former is the case as JFC102250 also superceded JFC101890 and JTN100000 which came during the "W" and "X" model years (1998 and 1999) but if so why are diesels like mine specifically excluded from the TSB mandating the installation of YMQ104590AA?

Help!
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

I am on a job at the moment, so using my phone and don't have all of the reference documents I have on my laptop (which is at home)..

However....

I will look in Rave when I get home tomorrow night/ Friday morning and see what the wiring is for the A/C clutch in a diesel model. It is possible that they had a relay in the fuse box to drive it to start with, or at least the MY diesel vehicle you have probably shipped with a later fuse box type already.

I suspect you can just install the HEVAC unit and all will be fine though..

I also wonder if the high current driver was actually removed from later HEVAC units.. Having had an earlier and later model together in bits next to each other, the boards do look pretty much identical. I wonder if the later versions are still actually capable of driving the clutch themselves, bit the harness upgrade (and subsequent fuse box upgrade/loom to include the relay) is more there as a protective measure so the HEVAC output can't be damaged by overload, as its now just driving a low curent relay coil, not the higher current electromagnetic clutch on the compressor...

Marty

Sent from my S4
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Hi

I do not have access to Rave at the moment. My laptop is under repairs.

The older units have load sensing build into the ecu. This means that the ecu is able to determine if the clutch is engaged or not. In case the pressure switch disconnects the clutch the ecu will cease signal to the clutch after a short interval and flag the book sign.
To overcome the problem that the voltage to the clutch via the ecu is too low, land rover come up with the extra wiring loom and the relay to indirectly power the clutch. The operation of the relay coil is not enough to have the load sensing working properly and because of that they incorporated a coil or heating element in the harness parallel over the relay coil to have the ecu working as intended. In the later versions they have the relay incorporated in the fuse box and the load sensing does not work the same as on the old units.

Hope this info helps. i bought the harness from Landrover Malaysia for less then RM 300 about 10 years ago and had it installed on my car.

Regards

Jos
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Top stuff, as usual guys.......

Marty- I'm holding my breath. I've tried to look thru my copy of RAVE and came up none the wiser. It does rather appear as if Land Rover intends JFC102250 to drive to compressor clutch direct as I couldn't find any mention of YMQ104590AA to be fitted to a diesel.

Jos.... my new fusebox (replaced 6 months ago at the beginning of all this) is AMR6477G which according to the Britpart website is intended for Diesels up to VIN WA410481, meaning that it is the correct part for my car and had my car been a V8, would require YMQ104590AA.

I'm still looking but if either if you guys find anything, please let me know.

Thanks much!!
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Right guys I think Iv got my head around this I will try removing the air distribution servo via the instrument pod and feeling by hand how tight the distribution flaps are, hopefully it's just a servo Iv ordered a set of three but if it's the flaps stuck I'm going to try and force the two halves of the heater box apart with some self tappers inserted from the front fascia through the clock pannel. Just one more question is it safe to power the car up with the instrument pod out to test the blend motors?
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

If I remember correctly you will almost certainly cause a SRS fault if you went that way. Go check out the technical pages here on rangerovers.net regarding dashboard removal. Jos here actually details a blow-by-blow procedure which is easy (HAHAHAHAHAHA!!!!!) to follow. You'll not need to go the whole hog of course since you're using the instrument pack shortcut but the information about the SRS issue is there.

What I have in mind (and I AM guessing here) is you'll need to drive the blower motors with 12v direct. Theres some info on how to access them at http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/58274-drivers-side-lh-blower-motor-removal-97-p38.html and maybe in the technical pages too.

Once you have them running then you can twist the white bit until you have air coming from the vents of your choice.

Alternatively, if the tapping screw thing works and the white bit moves easily after that then you could splice one of your new replacement blend motors into the harness, replacing the existing one.

Good luck!

Btw- those motors will draw up to 30A- at least that's the fuse rating for them.
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Hi

I do not have access to Rave at the moment. My laptop is under repairs.

The older units have load sensing build into the ecu. This means that the ecu is able to determine if the clutch is engaged or not. In case the pressure switch disconnects the clutch the ecu will cease signal to the clutch after a short interval and flag the book sign.
To overcome the problem that the voltage to the clutch via the ecu is too low, land rover come up with the extra wiring loom and the relay to indirectly power the clutch. The operation of the relay coil is not enough to have the load sensing working properly and because of that they incorporated a coil or heating element in the harness parallel over the relay coil to have the ecu working as intended. In the later versions they have the relay incorporated in the fuse box and the load sensing does not work the same as on the old units.

Hope this info helps. i bought the harness from Landrover Malaysia for less then RM 300 about 10 years ago and had it installed on my car.

Regards

Jos
Hi Jos,


Just wanted to tell you that after checking with a couple Landrover Malaysia guys, as well as here and on other sites on the 'net, I just went right ahead and plugged in my new JFC102550 in place of the old AWR1012 without making any other changes or modifications.


It works just fine.


I think you're right on the money with your analysis above and that the caution on Stockholmviews (that you'll kill a new-type ECU if you plug it into an older car without the harness) might be a little over stated.


I'M GUESSING HERE but it could be that installing a new-type HEVAC ECU in an older car without the extra harness might keep throwing up the book sign but it won't "kill" the ECU outright.


I also think that the harness is necessary only on the v8s due to a quirk either on the electronics of the v8s or the diesels. It could be that the diesels were specifically excluded from TSB0010 because their HEVAC ECUs had no trouble supplying the required current to the compressor clutch due to some quality of the electronics elsewhere in the car.


Let me run the car a while n report back if anything goes "bzzt".


In the meantime, if you're still in town over the extended weekend, it'll be great to meet up! I think I'm finally getting over the blasted dengue.
 

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Re: AC/HEVAC/Compressor Clutch confusion..... A solution? Maybe.....

Hi

I am glad that you are feeling better, and that your cars interior is comfortable for driving again.

Unfortunately I am booked on a flight tonight to go back to work for the next 7 weeks. I will send you a text message when I am back in town.

Jos
 

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Hi Jos,


Just wanted to tell you that after checking with a couple Landrover Malaysia guys, as well as here and on other sites on the 'net, I just went right ahead and plugged in my new JFC102550 in place of the old AWR1012 without making any other changes or modifications.


It works just fine.


I think you're right on the money with your analysis above and that the caution on Stockholmviews (that you'll kill a new-type ECU if you plug it into an older car without the harness) might be a little over stated.


I'M GUESSING HERE but it could be that installing a new-type HEVAC ECU in an older car without the extra harness might keep throwing up the book sign but it won't "kill" the ECU outright.


I also think that the harness is necessary only on the v8s due to a quirk either on the electronics of the v8s or the diesels. It could be that the diesels were specifically excluded from TSB0010 because their HEVAC ECUs had no trouble supplying the required current to the compressor clutch due to some quality of the electronics elsewhere in the car.
.
I know it's been a couple of years, but as an update to this, now that I've had HEVAC units from all ages/types apart on my bench...

The later model HEVAC units CAN be used in older vehicles to drive the compressor clutch directly (if required - they might not pull it in completely if the clutch faces are wearing!). Looking closer at the driver circuits on the later boards, nothing is different - they still use a MOSFET to drive the output - but my guess is that the error sensing (that was what told the HEVAC that the AC clutch wasn't operating on older vehicles) was either bypassed, or the firmware was changed to ignore that input.

The theory still applies that an older HEVAC in the newer vehicles will still need something to tell it that the load is there, even if it's just driving a relay - but you won't kill a new unit in an older vehicle, like once feared!

They joys of a couple of years more experience, and actually having had time to pull the units apart and inspect the boards a bit more thoroughly!

Marty
 

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hi marty!
so would i have problems if i replace my awr5051 in a 1997 RR hse 4.6L with an awr1012? would i need to add a relay or do anything for it not to give me any problems. sorry to sound redundant. i just want to make sure because I just bought one thats an awr1012, and i traded my awr5051 for it, so i can try to return it if awr1012 wont work on mines. thank you very much and ave a good day!
P.S. also sent you a message here thanks!
I know it's been a couple of years, but as an update to this, now that I've had HEVAC units from all ages/types apart on my bench...

The later model HEVAC units CAN be used in older vehicles to drive the compressor clutch directly (if required - they might not pull it in completely if the clutch faces are wearing!). Looking closer at the driver circuits on the later boards, nothing is different - they still use a MOSFET to drive the output - but my guess is that the error sensing (that was what told the HEVAC that the AC clutch wasn't operating on older vehicles) was either bypassed, or the firmware was changed to ignore that input.

The theory still applies that an older HEVAC in the newer vehicles will still need something to tell it that the load is there, even if it's just driving a relay - but you won't kill a new unit in an older vehicle, like once feared!

They joys of a couple of years more experience, and actually having had time to pull the units apart and inspect the boards a bit more thoroughly!

Marty
 

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AWR1012 should work on your vehicle just fine.

AWR5051 was the next revision of the HEVAC controller, but nothing changed vehicle wiring wise in the vehicles until later in the production run.
 

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Hi guys

Im also getting in on this old thread. I have a 98 Gems and the snowflake and 0 degrees is always present and the AC won't blow cool because of it. At some rare occasions it shows the correct temp and the AC works fine then.

Now I am thinking about getting a JFC102550 Hevac unit and hopefully it will fix the problem. I am a bit confused regarding the Vin numbers and part numbers, relay, hacks etc.
My vin is WA407242 the car is a 4.6 98 Gems and I have the ambient temp sensor behind the bumper. Would JFC102550 be the correct unit?

Also do I need any diagnostic tool to calibrate the new Hevac unit or is it a remove refit job?

Thanks
/Erik
 

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If the sensor works sometimes, then it is probably worth checking the sensor and the connection to it... I've seen a couple of P38's now where wires in that area down the front have got corroded and caused the problem or an intermittent connection. The later ECU's which have the sensor down the front by default (rather than earlier vehicles with it moved) also won't automatically update the temperature until the vehicle is moving - I think to make sure it's a clear stream of air, rather than picking up latent heat from the engine for example.

According to the parts table I posted above, for your VIN number either JFC101890, JFC102400, or JFC102550 will all work with no problems.

If you decide to swap the HEVAC, and struggle to find one reasonably priced locally, then I have some reconditioned units that I sell on exchange and could ship to Sweden if required.

I would check the wiring carefully first though, as it could just be an intermittent break in the wire which is causing it to not read properly at times.

Cheers,
Marty
 

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That's great Marty. I'll start out with the temp sensor. My local dealer have it in stock. I'll pm you when I decide to go for a new unit.

Thanks
Erik
 

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I have tracked down a JFC102550 Hevac unit locayl and I will check it out to see the condition.
But now a new AC related thingy have shown up. When car starts up and it shows 0 degrees no AC, driving for a while and temp rises the clutch kicks in and it works fine. Though when outside temp reaches above 20 degrees it stops again and only blows warm air. The 0 degree thing I can live with because when it reaches 4 the AC actually kicks in but above 20 is a big problem.

When I drove home tonight it was steady 18 degrees outside and climate control inside the car was perfect. During the day it was about 24 and the inside was horror.

Now to the question that Marty might have an answer to?
Would the
JFC102550 Hevac unit also cure this issue or is this something else?

Thanks
/Erik

 

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I had exactly the same problem, at anything over 24 degrees the clutch wouldn't engage but would when it was cooler. It might be an electrical problem, it might be that you are low on refrigerant (so the pressure switch isn't allowing it to engage) or it could be, as mine was, the compressor clutch air gap was too large. When it won't engage, with the engine idling and the temperature set on Lo (to force the AC to come on), tap the clutch with a screwdriver handle. If it clicks in and engages, it is the air gap. There should be a gap of between 0.017 and 0.031 inch (0.4 - 0.8mm) and it is preferable for it to be nearer the lower figure. If it is too large, hold the clutch outer and remove the central nut. The clutch outer is on splines and simply pulls off and there are shims behind it. Remove shims until the gap is correct.
 
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