air conditioning problems s3 8p

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dmc_s3_8p

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The AC recently stopped working in my 2008 s3. Might need regassing but when I turn it on and the econ light goes off, the radiator ac condenser fan does not come on. My question is, should that fan start as soon as I press the econ button?

I ran a vcds scan and there are no errors from hvac.
Leading up to this, there has been a slight low pitch speed dependent howl when the ac was working which seemed to come from under the dash rather than the compressor.

Any pointers on things to check would be greatly appreciated.
 
Check G65 pressure switch, bottom right of radiator drivers side, common issue.

Fan wont always come on with ac, summertime it does generally.
 
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Thanks will check the G65. Funny thing is the econ light stays off, like everything is ok, but no cooling. Glad to hear the fans don't immediately start when the ac is switched on. Funny that there are no error codes on vcds. I need to check the pressure in case it is just that... but that would be lucky!
 
If it is the pressure you need to investigate why. Potential leak. Switch is a good way to start had the same issue on my a6 but a scan showed an error.
 
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Agreed, thanks. I recall now that this switch was changed under warranty when I first got the car (10 years back!). What it failed, the Econ light would not switch off and the AC wouldn't switch on. I didn't have vcds at the time and didn't follow up because it was all covered under warranty (just). I think the sensible thing to do now is start with checking the current pressure and decide what to do from there - if it's completely empty then thorough check for leaks, if there's some pressure in it perhaps a re-charge?

I've ordered a gauge!

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Yeah the G65 can be a pain, sometimes shows error sometimes doesn't, but for the cost its worth changing as can do yourself, little tricky but once undone you can turn by hand usually.
 
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Thanks. I guess even though this was changed, it was 10 years ago! This will be first culprit on my list to check if the pressure is at zero! Hopefully I'll find it before I get to the compressor!

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Ok, the plot thickens. Gauge arrived and I measured the static AC pressure on the low pressure side. It's reading way too high at 65psi with the engine/AC off. So I definitely don't have a leak, but what causes it to be so worryingly high?

Maybe that pressure valve has gone with no error codes after all?

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Does it need to be on and circulating to get true pressure? Genuine question as I don’t know.
 
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Yes, I did wonder about after I disconnected everything! I'll try that next.

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abmat said:
Does it need to be on and circulating to get true pressure? Genuine question as I don’t know.
Click to expand...
Ok just checked with AC on. You were correct, pressure drops from 65psi as AC starts to 12psi. So it seems I may just need a recharge?

Also tested radiator/condenser fans with VCDS and all working fine. No error codes from G65, N280.

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Easiest diagnosis is to have a re gas with one of the automated a/c machines, about £50. You just need to use your local trusted garage. Hopefully it is just down on pressure, probably never been done since the car was built. Mine was last re gassed in 2012 and just started to struggle to keep the car cool
 
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SootySport said:
Easiest diagnosis is to have a re gas with one of the automated a/c machines, about £50. You just need to use your local trusted garage. Hopefully it is just down on pressure, probably never been done since the car was built. Mine was last re gassed in 2012 and just started to struggle to keep the car cool
Click to expand...
Yes, agreed! In hindsight it would have been the quickest option. I like to try and figure out how things work though and see if I can fix them first! You are correct though. The car is 2008, the pressure switch was changed in 2011. So the AC was last re-gassed either when new, or at the very minimum 10 years ago. It's amazing it worked at all up to this point. It's a testament to the build quality of these cars... though I'n not suggesting they should not be regularly maintained! Thanks!
 
NHN said:
Check G65 pressure switch, bottom right of radiator drivers side, common issue.

Fan wont always come on with ac, summertime it does generally.
Click to expand...
Thanks for prompting me to check the fan operation. I spun them both up on demend yesterday with VCDS and a relatively cold engine.
After this when the engine was up to 90 C, so I removed my Ross Tech cable and checked that when I switched the AC on both fans started up fine as you said they would in summertime!
Luckily, it looks like the problem is just low pressure in the system which I measured yestreday at about 12 psi. I'll top it up and hopefully that should be the end of it!
Thanks for your pointers...
 
abmat said:
Iirc I think you can read the pressure using vcds too
Click to expand...
Apparently so, but I couldn't find exactly where It wasn't under the HVAC output settings. Think I need to spend some more time better understanding VCDS!

Ok figured it out under measurement blocks!! Thanks!
 
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