Failed sanden (SD7) compressor autopsy (with pics)

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EDC5
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Failed sanden (SD7) compressor autopsy (with pics)

Post by EDC5 »

The new C5 in the family was bought with a non-functioning AC system and a strange metallic rattle sound. After removing the Aux belt and spinning the alternator and air con compressor pulleys, it was clear that the sound was from the AC comp.

Yesterday I replaced the failed compressor with another from eBay that claimed to be working and cost £18 including delivery.... we shall see for how long it continues to work; however, this cheap eBay compressor has sorted the rattle and the air con blows nice and cold.

Today I decided to dismantle the old compressor to try and find why it wouldn’t engage and what was causing the rattle in addition to the reason why there was hardly any gas in the system (<5psi).
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This is the compressor removed from the car, what is immediately obvious is that the coil wires have been ripped off... so that explains why the compressor wasn't engaging. At this point by spinning the pulley by hand the metallic noise appeared to be from the clutch coil rotating with the pulley!
Somehow the clutch coil electromagnet had detached from its mounting and was rotating at full engine speed, thus ripping the wires off.
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After removing the clutch, pulley and some circlips I removed the electromagnet coil and could see what the issue was. There should be a locating nub on the coil (circled in orange) that located the coil, but on this one it had been worn down somehow.
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Similarly on the compressor body the holes that the nub should sit in seem worn and show evidence that the coil has been rotating with the pulley.

So that concludes the main autopsy. It turns out that it is easier to buy a known working (apparently) compressor on eBay than it is to just buy a replacement coil, so that's what I did.

The next bit is of the autopsy is still interesting to me as it could explain why the gas mostly leaked out.
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This corrosion on the main shaft lies directly where the end seal is located on the sanden and perhaps explains the leak. I also found oily residue on the clutch plate suggesting that at some point oil (and refrigerant) had left the system via this seal and dripped down.

For that reason, I'm glad i didn’t just get a new coil and replace that as I'd almost certainly have had to replace the compressor itself once I found that it wasn’t holding gas.

The next pics show the compressor at minimum and maximum displacement:
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and this final picture shows the amazing piston arrangement:
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All in all, these are amazing devices and barring corrosion on the shaft the rest of it was in great condition.

Hopefully the replacement compressor lasts a good while otherwise I might consider the possibility of rebuilding one with new seals and gaskets.
Last edited by EDC5 on 15 Aug 2020, 21:00, edited 1 time in total.

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white exec
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Re: Failed sanden (SD7) compressor autopsy (with pics)

Post by white exec »

Well done in stripping that down, and photographing the innards so well.
First time I've seen the mechanical arrangement. Not dissimilar to an LHM pump.
Hope the 2/h pump does its stuff!

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EDC5
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Re: Failed sanden (SD7) compressor autopsy (with pics)

Post by EDC5 »

Thanks, yeah it really is an amazing piece of design; especially the ability to vary the displacement on the fly with an electrical signal.

I've found a new main shaft seal on AliExpress for £3, fairly tempted to buy it and have a go replacing the seal, possibly as an academic exercise only.
Not sure how the shaft could be reconditioned though where the corrosion is so may be pointless.