Help Please A4 air con problems

[vanbasten]

So I have been having issues with my air con - air con button red light comes on but no cold air - system was regassed
recently.

Fitted a new pressure sensor tonight and now air con button light won’t stay on - light only stays on if I hold the button in.

Can anyone advise?


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[rum4mo]

The best approach now would be to scan this car using a diagnostic tool like VCDS or even Carista as both of them can access the AC controller and so will reveal any stored faults and let you see the system pressure when the engine is not running.

If your original pressure sensor was faulty and stopping the system working, then even although you have replaced the pressure sensor with a new latest version genuine VW Group part, the fault codes from the original one will have been left in memory. If that original pressure sensor was not faulty and you have replaced it with the latest version of genuine VW Group part, then there will be no fault code relating to that sensor, although, if the gas pressure is too low due to a system leak, then there will be a fault code logged for that.

Guessing while sounding a good first attempt at fixing things usually kicks you in the wallet/teeth.

 

[vanbasten]

Had carista ordered and hoping it arrives today - will update on scan results then


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[vanbasten]

Well carista arrived and have done a scan.

With old pressure sensor in I get a reading of 4 bar with air con off and it increases to 6 bar when air con is switched on, but no cold air

When I put new sensor in pressure drops to 1 bar and air con doesn’t stay switched on.

Am even more baffled now


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[rum4mo]

Well that is not good!

Is the new sensor a genuine latest version from VW Group?

 

[vanbasten]

Well that is not good!

Is the new sensor a genuine latest version from VW Group?

No it’s not a genuine one - had tried an eBay special in the hope of a quick fix - would you know part number of genuine latest version one?


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[vanbasten]

No it’s not a genuine one - had tried an eBay special in the hope of a quick fix - would you know part number of genuine latest version one?


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I can understand that the new sensor may be a dud and throwing error codes

but can’t understand the old one showing pressures, no error codes but yet no cold air.

 

[rum4mo]

I think that your original one seems to be working okay, so I'd suggest refitting it, I 've only ever replaced one pressure sensor and I bought a new O-ring seal for it and smeared it with oil con comp oil so that it did not "pick up" when being refitted.

The reading when the engine is not running of 4Bar is okay for R134A but I'd be expecting more like 8.2>8.6Bar when demanding cooling, either there is something that is stopping the AC seeing a cooling demand, or the compressor is not working too well, but nothing is actually causing a fault code to get logged. I think that this job has moved out of the "reach" of getting help from Carista, VCDS which costs a lot more can "get into" the controller and let you see if the temperature flap motor is demanding cooling etc etc etc, maybe time to find someone close to you that has VCDS and knows how to use it wrt the AC system.

 

[vanbasten]

Thanks rum4mo, will have to try and find someone with vcds close to me in Northern Ireland that can help


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