D1 300TDI AC compressor shuts off and won't restart until the car is turned off then back on

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J

JimmyOlds

Member
Posts
11
Location
New Zealand
Hi guys,

I've got a bit of an odd problem with the AC in my 95' Disco 1 300TDI (automatic so it has an ECU rather than manual diesel pump). The air conditioning will work periodically, but once the car has been driven for a while the compressor clutch will stop engaging. If I turn the car off then back on again it resolves it for a brief period of time, but eventually it seems to stop again. I've measured the low pressure side at idle and around 10 degrees C to drop to around 25PSI when the compressor engages, which I believe to be within spec. I've tried reading through the RAVE but don't really have the best troubleshooting skills. Could anyone point me in the direction of what conditions might cause such a failure? If it makes any difference I also have a 96' V8 D1 with perfectly functional AC so if there are any parts I could swap between to see if it eliminates the problem (without releasing refrigerant) I could try that.

Cheers,

James
 
Hi James. Well as the compressor clutch is electrically operated it’s more than likely an electrical fault, maybe within the clutch or in the control circuits, so basic stuff.
Turning the ignition switch to ‘0’ for a reset should be the same as using the AC on/off switch.
So with the simple circuit diagram found in the Haynes workshop manual and a multimeter, from the start with the 12v supply to checks that the relays, there’s more than one, aren’t going faulty intermittently, or be the clutch coil or an iffy electrical connection maybe.
In other words what ok when the clutch is engaged and what’s missing when the clutch disengages. RAVE will help with the functioning of the AC system also diagnostics maybe.
 
Maybe something else is going wrong and taking the signal away from the ac relay, ie engine overheat?
 
lynall said:
Maybe something else is going wrong and taking the signal away from the ac relay, ie engine overheat?
Click to expand...
But then the EDC engine control module doesn’t have an engine temperature sensor, or have i missed something?
The EDC does have control of the A/C logic relay and the compressor clutch relay, but firstly in fault finding… in this instance is are these relays functioning correctly.
 
discool said:
But then the EDC engine control module doesn’t have an engine temperature sensor, or have i missed something?
The EDC does have control of the A/C logic relay and the compressor clutch relay, but firstly in fault finding… in this instance is are these relays functioning correctly.
Click to expand...

Iirc if the car overheats or think it is overheating, the car switches off the a/c to reduce engine load and switches on the a/c fans to help with cooling?
 
lynall said:
Iirc if the car overheats or think it is overheating, the car switches off the a/c to reduce engine load and switches on the a/c fans to help with cooling?
Click to expand...
Yes partly correct
If in hot climates the engine is working hard and the temp gauge goes up into the red the A/C will switch off to reduce load on the engine, when the temperature is lower the A/C will switch back on. The A/C doesn’t at the same time leave the fans switched on.

With the D1s if the A/C is on the the fans will run unless there’s an issue is detected with the system, then the clutch will disengage and therefore the system is off.
If the engine or engine bay gets expensively hot the A/C fans will switch on to add cooling, for an example with my disco on hot day when parked up after a run when the A/C is on the engine bay gets very hot, so after a couple of minutes the fans kick in, all done by the simple coolant thermostat and timed for around 10 minutes I believe, I've never stood around to find out. :)
 
When I bought my 300tdi years ago the AC didnt work, the issue was a faulty thermo switch which is near the thermostat housing, as others have said this switches off power to the AC magnetic clutch when the engine water temp gets too hot and you want all water cooling to go towards getting the engine back to normal temp, this sensor was “open circuit” on my car (it should normally be “closed”) so I simply joined the two contacts with a piece of wire and the AC then worked. I bought a new switch a couple of years ago and this post has reminded me to fit it....oops.

So I would start by checking power is getting to the magnetic clutch when the fault is occurring, and if it isn’t then check if power is getting to the thermo switch, and that the switch is closed and letting power get to the clutch.

Not all auto’s have EDC, mine doesn’t. I think it depends on what market the car went to, when new.
 
KiwiTDI said:
When I bought my 300tdi years ago the AC didnt work, the issue was a faulty thermo switch which is near the thermostat housing, as others have said this switches off power to the AC magnetic clutch when the engine water temp gets too hot and you want all water cooling to go towards getting the engine back to normal temp, this sensor was “open circuit” on my car (it should normally be “closed”) so I simply joined the two contacts with a piece of wire and the AC then worked. I bought a new switch a couple of years ago and this post has reminded me to fit it....oops.

So I would start by checking power is getting to the magnetic clutch when the fault is occurring, and if it isn’t then check if power is getting to the thermo switch, and that the switch is closed and letting power get to the clutch.

Not all auto’s have EDC, mine doesn’t. I think it depends on what market the car went to, when new.
Click to expand...


I think EDC on UK autos was std from N reg 95 onwards, 122bhp as opposed to non EDC 111bhp!
 
KiwiTDI said:
When I bought my 300tdi years ago the AC didnt work, the issue was a faulty thermo switch which is near the thermostat housing, as others have said this switches off power to the AC magnetic clutch when the engine water temp gets too hot and you want all water cooling to go towards getting the engine back to normal temp, this sensor was “open circuit” on my car (it should normally be “closed”) so I simply joined the two contacts with a piece of wire and the AC then worked. I bought a new switch a couple of years ago and this post has reminded me to fit it....oops.

So I would start by checking power is getting to the magnetic clutch when the fault is occurring, and if it isn’t then check if power is getting to the thermo switch, and that the switch is closed and letting power get to the clutch, never had to touch it like the rest of the system.

Not all auto’s have EDC, mine doesn’t. I think it depends on what market the car went to, when new.
Click to expand...
When the diesel got its EDC that that took over from the thermo temp sensor. My disco has the thermo switch in the thermostat housing.
 
discool said:
It was the 1996MY disco so back then it was available and in the showrooms in mid 1995 along with the new XS.
in popped in to have a look at while my RR was in fo service.
Click to expand...

Me and the missus looked at an XS model on an N plate in Red with the jazzy trim down the sides, thought it was real smart.

Like this,

Screen Shot 2021-09-20 at 03.29.50.png
 
Here is a pic showing the A/C switch (hex shape) at the bottom and thermo housing at the top.

Slightly off topic is the pic of the VIN which I have always thought was for a 96 MY, and the (I hope) mechanical injector pump. Engine is 20L3607.

CE718E79-94FE-47B6-80F7-CCD9C36DD017.jpeg
D8A86162-77E9-4E7F-B890-2F7A124107C1.jpeg


D75406C5-F35D-4C28-9428-7C42EE9A7537.jpeg
 
Discool, you got me googling, and I found this, which (if true) means you need the VIN and engine no. to tell what “should” be in the car, I have no idea how correct this info is, it’s from a different forum.....my VIN had the “F” in the 8th digit position which appears to explain why it has no EDC.
I don’t know if it has a CAT (but it does have a flexi pipe on the down pipe), or EGR.

“Some Tdis (engine serial prefix 23L) have Exhaust Recirculation Regulators (EGRs) or Electronic Diesel Control (EDC) which limit the “mechanical only ” nature of these pre-Td5 engines. Which engines have these features seems to be unrelated to their year built, but you can tell from the VIN number. The character after the body type shows the type of engine, e.g. SALLDHMF – 110 SW 200Tdi/300Tdi without EDC/Cat or SALLDHA6 110 Hardtop 200Tdi/300Tdi with EDC/Cat. The last character, F or 6 refers to the type of engine in the Land Rover.”
 
So “k108” needs checking out.....to see what it is doing when the clutch should have power but doesn’t.
 
KiwiTDI said:
So “k108” needs checking out.....to see what it is doing when the clutch should have power but doesn’t.
Click to expand...
Well thats simples, its either open and the clutch isn’t energised, or closed and the clutch isn’t.
The 12v supply to the relay coil is more important and the device that gives that supply to it, the ECM if the engine is fitted with one.
 
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