Traintester

Traintester

New Member
I know this is a perennial problem but here I go any way! My air con isn't coming in when requested. Other than this, this is my first Disco and I'm extremely pleased with it! I haven't been able to find any questions anywhere that are similar to mine so this is why I'm asking here and now.:confused:

I have an 02 TD5 ES with rear air con. I've had it re-gassed, the dual pressure switch tests fine (N/C) so I know it has the right amount of gas. There are no faults coming from the ACU. I have tested the compressor clutch by manually bridging the control relay in the engine compartment and it blows cold. There is a 12 volt positive feed to the coil of this relay but no earth. From the Electrical circuit diagram if I am reading it correctly I think the ECU does earth switching to control this relay but I need some expert input to see if I'm on the right track before I either go any further myself or give it to someone I have to pay! What voltage am I expecting to see coming out of the ACU from the compressor clutch request output?

I don't know if it could be related but while I was under the passenger side foot-well yesterday and there are two green wires in their own loom that are not connected to any plug connectors, I need to do more research or look at another D2 to find out where they go but I think the ECM is under the bonnet and not down here so maybe a red herring???...
 
watch the screen... if you see ''ECON'' on the left upper side that's your problem... push the ''econ'' button to deselect it.... and by the way, are you in Africa?... cos the set temp must be lower than the outside temp for the clutch to engage
 
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12v at the compressor clutch. Earthed through the ecu sounds fairly logical. First thing on my mind is a broken wire, loose connection etc. A diagnosis should bring this up
 
Traintester said:
Hmm, what if the sun is shining (lots of glass in these discos) and the cabin temp rises above the exterior temperature?!
Click to expand...

Centre of the bottom of the windscreen is a little plastic lump. There's a photocell in it which senses when the sun is shining through the windscreen and signals the A/C accordingly.
 
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Ok, done some more fault finding.

I have now found that the refrigerant has leaked out since my last fault finding but there was enough pressure then to keep the dual pressure switch closed so my previous findings still stand. For now (until I can get the leak found and fixed) I have bypassed the switch but am only demanding the clutch for very short intervals for fault finding purposes.

Here is what I know -

I have no faults showing when I do the manual fault code retrieval from the ACU (apart from last night when I got a fault from one of the solar sensors - it was going dark... d'oh!)

I have correct continuity from the ATC to the dual pressure switch and through to the ECM under the bonnet.

Also continuity from the earth switching wire of the ECM to the earth side of the compressor clutch control relay in the under-bonnet fuse box.

I have 5v signal coming from the ATC compressor clutch request wire (with the dual pressure switch disconnected).
Q . Has anyone else checked the voltage coming out from ATC yellow/black wire C0793-11?

I have 14v coming from the yellow/black ECM input C0658-9 yellow/slate B9 wire (compressor clutch request from ATC) with the engine running. RAVE says this is input B9 that accepts 0 -12v.
Q. Does this mean that ECM is cooked in this area and therefore never going to switch the earth side of the aircon relay?

Thanks folks!!!
 
are you certain that ALL the conditions for compressor clutch request are met?

1. cabin temp greater than ambient temp and the set temp lower than ambient temp ... otherwise the system "knows" it's enough to blow the outside air into cabin to cool it without compressor involvment ...so it's not enough to have greater cabin temp than outside but lower set temp too...that's why i asked about Africa...cos if you are in UK and e.g the ambient temp when you make those tests is let's say 16*C you must have at least 17*C in the cabin and set 15*C to get a clutch request... got it now?
2. evaporator temp sensor is properly working(unfortunately this one is not covered by diagnostic).... not very common to fail though

if the temperatures are not like at point 1 there will be no clutch request...period
 
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Ok,

So the next step in this process will be to get the thing good and hot inside after a run, get a hot cloth and wrap it around the ambient temp sensor, this cloth I will call 'The Cloth Of Sahara' :D , then I'll set the cabin temp to 16 after checking the outside temp is good and warm. I might try to get 'The Cloth of Sahara' above 30 c (might try a hand warmer too) so that the cooling fan runs as well to test that function. Good test plan? You are very patient! It's all much appreciated...
 
Got it nice and hot inside and had the ext temp reading 39 thanks to the wife's hairdryer. Set the inside temp to 16.

All compressor clutch request criteria fulfilled and still no compressor clutch actuation.

Still got the 5v coming from the ATC when set to AUTO, 0v when set to ECON, still got the (I think) eroneous 12v coming from the clutch request input of the ECM.
Just to prove that the ATC is working ok on other circuits when it's in AUTO and everything is hot as mentioned above the cooling fan demand functions correctly and so does the fan.
:confused:

Just a quick question - if it's frosty and the air inside the car is damp from condensation, so the outside temperature will possibly be 0 or less, the inside temperature will be 2 or 3 and the requested interior temp is 22, will the air con not work in order to dehumidify the air and dry the interior out?
 
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it seems you emulated the environment for a compressor clutch request then
continue digging but be aware.... that feed on C0658-9 is not eroneous, you must have it for compressor clutch activation, the relay will close with this feed and with earth path from pin 29
DESCRIPTION AND OPERATION 18-1-43 said:
The operation of the A/C request is via a switch being connected to earth. Voltage is supplied via pin 9 of connector
C0658 of the ECM, at the point at which the switch is pressed the connection to the earth path is made and the
compressor clutch is engaged.
The ECM provides the earth for the relay windings to allow the compressor clutch relay contacts to close and the
compressor clutch drive to receive battery voltage. The ECM uses a transistor as a switch to generate an open circuit
in the earth path of the relay windings. When the ECM closes down the earth path, the return spring in the relay will
pull the contacts apart to shut down the compressor clutch drive. Fuse 6, located in the engine compartment fuse box,
provides voltage to the compressor clutch relay switching contacts. The relay windings are supplied with battery
voltage from the main relay, also located in the engine compartment fuse box. The earth path for the relay windings
is via pin 29 of the ECM connector C0658. When the relay is energised the output from the switching contacts is
directly to the compressor clutch.
Click to expand...
 
Looking at the circuit diagram, the positive for the compressor clutch relay coil is actually fed from RELAY-MAIN (R100) which comes on with the ignition via the inertia switch, it's only the negative that is switched by the ECM when it gets a signal from the ATC, I think that's what the quote you put in from RAVE tries to say although the language is a little ambiguous perhaps. I think the request voltage comes from ATC C0793-11 to ECM C0658-9 which tells the ECM to activate the transistor that then closes the negative path for the relay coil on C0658-29. My theory is that it's this transistor that is either damaged or the ECM is incorrectly configured. But I stand to be corrected.

By the way I really appreciate all the time you've obviously put in to these replies, it's made me think hard and check and recheck the schematics. I'm going to check the state of that voltage that is coming out of ECM C0658-9 in various states, ignition off, ignition on - engine off, ignition on - engine on just to see what's going on that end. I think this is erroneous as it is there whether the ATC is set to AUTO, ECON or OFF....

And Nanocom is on the way, I think it may help me in the end.

:)
 
C0658-9 is the aircon request which goes through the dual pressure switch and feeds the aircon ECU.... and yes the compressor relay coil has feed from main relay and you must get earth path from pin 29 as the relay to engage
 
In the end it turns out it was the air con control unit inside.

And by the way the external temperature does nor have to be higher than the set point inside, have spent lot of time watching things with nanocom.

Now to change the leaky output seal on the transfer case.

Thanks for the help though.
 
Hi can anyone tell me if i put 12v in to the 2 pin plug on the pump will this engage the clutch ? appreciate the thread is a year old so may have gone cold ..joke there i think :)
 
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12V there will engage the clutch only, the pump will work only with engine running and clutch engaged... you can do that by bridging the relay's contact too for test (put a wire instead pins 30-87 of relay 11 engine bay)...but dont run the engine like this if you dont have gas in the system cos you'll ruin the compressor, that's why the dual pressure switch cuts it with low pressure
 
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