Mk5 Golf GTI air con not working- diagnosis & repair

[insanitybeard]

I was asked to help try to sort out an air con fault on one of the extended family's cars recently- a Mk5 Golf GTi. The air con had apparently recently stopped working, and a quick check of the system revealed that there was zero gas in it so obviously a leak somewhere. Not having the kit myself I took it to the same guy that regassed my Galaxy a while ago- a shout out to Charlie from Auto AC in Tiverton! After a quick test of the system using nitrogen it was obvious that there was a major leak as it could be heard at the front of the engine bay. However, some testing with leak finder spray and sniffer had proved inconclusive, it sounded as if it was coming from the compressor area but the access was too limited as the compressor is below the alternator. After removing the alternator to give better access, there was no obvious damage or leak from the compressor , but after a bit more probing the leak was found to be coming from the pressure switch- but not from the thread or o-ring seal at the base of the switch, or even the body of the switch, the gas was escaping up through the core of the switch and escaping through the connector body, which is why we'd struggled to locate it- the mulitiplug connector was effectively diffusing the gas! That's a new one on me, fortunately the local branch of TPS had a genuine sensor which they delivered the same afternoon allowing the fault to be rectified and the system regassed in the same day, which was a result- I had been expecting to find a leaking condenser which would involve me taking the vehicle away to repair before returning another day for the regas! The switch was around Ã,£60 and has been modified, the original had an approx. 17mm (?) hex under the connector which was not easy to access- it needed a crows foot spanner to get on, whereas the replacement had a much bigger hex which allowed a conventional socket to pass over the connector housing and unscrew/ tighten it from the top.

Old sensor:
[attachimg=1]


Top view of compressor (alternator removed) showing the port where the switch threads on to (arrowed):
[attachimg=2]

[johnnyroper]

Wonder if it's vibration related due to way it mounts rather than simple failure of switch?

[insanitybeard]

Could be related to vibration over a long period of time I suppose, there's no obvious sign of damage to the old switch but it's obviously failed internally allowing gas to escape from the transducer 'chamber' within the switch. Looks like the Touran uses the same switch so if the air con packs up on that, the switch will be the first thing I check!