D4 AirCon issues

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Originally Posted by shack

Under what circumstances does the clutch operate on a 3 litre?

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Don't know. It's not discussed in the workshop manual I have, but it is on the wiring diagram.

Edit : I wonder if it's related to lubrication. On the 2.7 when the AC is off the compressor still runs at minimum displacement. That's going to very slowly carry oil out of the compressor and I'd wager some sits in both the condenser and evaporator. That'll return to the comp when the refrigerant flow increases, but perhaps when it's off for extended periods (like the Econ button is pressed) then there could be a time when the compressor has insufficient oil.

Being able to switch the compressor off completely would then prevent that from happening.

3L only turns off the compressor when you press the AC button on the dashboard. The rest of the time it’s engaged.

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Originally Posted by BradC

The 2.7L does not have an electromagnetic clutch.

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So what happens on a High or low pressure fault,if the compressor cannot be electrically stopped?

FWIW,as for oil return at low load,in non Auto air systems,smart systems will time the period of low load operation,then load up for a short timed period,then back to low load and repeat.

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Originally Posted by scarry

So what happens on a High or low pressure fault,if the compressor cannot be electrically stopped?

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You tell me? Fact is it doesn’t have one. As for the consequences of that in a fault scenario [emoji2373][emoji2373][emoji2373]

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Originally Posted by DiscoJeffster

You tell me? Fact is it doesn’t have one. As for the consequences of that in a fault scenario [emoji2373][emoji2373][emoji2373]

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Maybe for High pressure it has an internal relief valve,back into the suction side of the compressor?

Whether it has one or not the compressor will keep running and eventually fail,but having an internal relief valve will reduce the danger of high pressure refrigerant being released.

Seems a badly engineered system to me,but what would I know[bigrolf]

My 4.4 TDV8's compressor also has a clutch. It's engaged at idle even though the a/c is switched off but presumably disengaged in some circumstances, possibly on low and or high gas pressure to protect the system.

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Originally Posted by scarry

So what happens on a High or low pressure fault,if the compressor cannot be electrically stopped?

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On low pressure it'll just grind the compressor to dust. Under high pressure something will break or burst. In either case there's a sacrificial coupling in the compressor pulley that snaps to ensure a lunched compressor doesn't take out the other accessories on the belt.

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FWIW,as for oil return at low load,in non Auto air systems,smart systems will time the period of low load operation,then load up for a short timed period,then back to low load and repeat.

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Yeah, If I'm near the condenser when it happens the oil return cycle on our Panasonic sounds like a turbine spooling up.

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Originally Posted by BradC

On low pressure it'll just grind the compressor to dust. Under high pressure something will break or burst. In either case there's a sacrificial coupling in the compressor pulley that snaps to ensure a lunched compressor doesn't take out the other accessories on the belt.

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What a wonderfull set up[bigrolf]

I knew I shouldn’t have commented on this post. Yesterday my AC decided to do the failing valve trick by constantly cycling off and going warm. Turning off the AC (D4 3L) for a minute gets it going again, for a little while. Yesterday it was only working for minutes at a time.
Having just dropped $3.5k to fix the stupid EGR leaking into the cooling system and leaking oil cooler, I really don’t feel like spending more on this thing right now. Grumble grumble.

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Originally Posted by DiscoJeffster

It is under gas pressure so you will lose the gas so legally you need to get the gas recovered by a certified AC technician. The system will then need to be pressurised with nitrogen preferably which will help you to get the valve out. You will then change the valve and need to get the system regassed. After that you might see improvement, or not, depending on the health of the compressor.

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I got a comp from UK 830 inc freight