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D3 - Engine Bay Everything under the bonnet

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Old 6th January 2019, 12:21 PM
erubus erubus is offline
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Default AC compressor clutch?

Hi guys. I have been getting myself ready for taking the engine out to repair whatever damage has been caused by the broken timing chain. Obviously I need to discharge the AC system and disconnect several of the pipes.

The manual states that the system needs to be re-charged before starting the engine for the first time. I have read somewhere that there is no clutch on the AC pump and if it is run without gas then it will destroy the pump.

Is this the case? Obviously i don't have the equipment to re-charge the AC here at home so it would be a lot easier to put the engine back in and get the car running again then take it to get professionally done.

If it is the case that I really do need to re-charge it first, i will look into hiring the vacuum pump etc and do it here. It would be devastating to do that extra (expensive) step only to find the engine still doesnt run and needs to come back out again! (that would be devastating anyway!)

Gill
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Old 6th January 2019, 02:28 PM
MikkiJayne MikkiJayne is offline
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Do you have to actually remove the compressor to get the engine out? With D2s its possible to unbolt the compressor from the engine and just hang it off the chassis leg with a strap so the system doesn't have to be opened. Same with the PS pump on the V8s too.

The later compressors have an internal variable valve rather than a clutch. It seems highly suspicious to me that these would destroy themselves without gas pressure - if that were the case you'd need to replace the compressor if the system had a leak. Its natural for the gas to escape over time too. The compressor will need oil, but it already has that so as long as you don't lose much when you remove it that should mostly stay put.

Is there anything in the tech dump about changing the compressor or parts of the system? If not I can have a look in Elsawin later and see if it says anything about this.
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Old 6th January 2019, 05:19 PM
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snapdragon snapdragon is offline
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The compressor doesn't have a clutch. It has a breakaway' pulley. If the compressor seizes, the force of the pulley rotating flips some rubber parts and then it becomes a freewheeling pulley until it is replaced or reset. What you could do, is remove the pulley, take out the rubber blocks and refit so it is freewheeling. Or what about not fitting the belt and just start it for a few seconds and don't rev it the first time (NB revving without a belt on can damage the flywheel harmonic damper.)
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Old 6th January 2019, 07:50 PM
erubus erubus is offline
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To be honest I hadn't thought to look in the tech dump for info on the AC. I sent a fair bit of time reading the instructions (from the tech dump) for removing the engine and then stripping it down to replace the timing chains etc. It did mention in several places splitting AC pipes though.

If it is possible to do the job without doing so I would prefer that but as the front end needs to come off I think it's unlikely. The compressor itself can stay on the engine although it would probably need to come off to take the head off anyway.

Removing the rubber blocks would be a way forward though. I shall look into that.

Of course, it could all be not needed as the engine might well be too far gone to save anyway. Valves and rockers are cheap enough, but if it ends up having a cracked head then it's probably toast. If it's aluminium I could weld it if its an accessible crack but if its internal then obviously I can't. Also if it has cracked a piston then I really am screwed. When you start adding up the cost of all the parts, and then all the sundries, loil seals, gasket sets blah blah i'll be spending more than I'd be losing by scrapping the car. I just won't know until the engine is out and stripped apart!
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Daily drive: 2008 A8 4.2TDi
2003 A8 4.0TDi. 4 zone climate, double glazing, Bose - dead
Other cars: 1980 Land Rover Series 3, 2.25d, hydraulic winch,Van/station wagon/topless depending on my mood
1990 Land Rover 90 factory county station wagon with all the luxury additions, such as a clock and a tape player.
2007 A4 3.0TDi s-line cabriolet quattro
2000 A8 D2 2.8 quattro, looking for a new home - gone
2003 A6 3.0 quattro, in the way... anyone want any parts? - gone
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