So i wrote in this forum a few months back. Long story short;

 

My AC was blowing out warm. Took the S3 to Kwik fit, charged once, worked for a week then went cold, recharged twice. Happen again.

 

Took it to another place, mechanic said it looked like my AC wasn’t fully charged, he charged it this time it lasted for about a month at most…

What I recently noticed was that the pulley on my AC compressor was constantly rotating (+ internal clutch engaged and also rotating) even without the AC turn’t on.

Could this be the reason why my AC has gone warm? And would this also explain why some days the car drives a little rough.

Could this just be the case of changing the AC pressure switch?

Edited September 27, 2025Sep 27 by Unique

22 hours ago, Unique said:

So i wrote in this forum a few months back. Long story short;

 

My AC was blowing out warm. Took the S3 to Kwik fit, charged once, worked for a week then went cold, recharged twice. Happen again.

 

Took it to another place, mechanic said it looked like my AC wasn’t fully charged, he charged it this time it lasted for about a month at most…

What I recently noticed was that the pulley on my AC compressor was constantly rotating (+ internal clutch engaged and also rotating) even without the AC turn’t on.

Could this be the reason why my AC has gone warm? And would this also explain why some days the car drives a little rough.

Could this just be the case of changing the AC pressure switch?

Hi if the clutch is engaged all the time it is probably a relay fault, if you have had it recharged properly you most likely have a pin hole in the condenser unit or the radiator.

Steve.

On 9/28/2025 at 6:00 PM, Stevey Y said:

Hi if the clutch is engaged all the time it is probably a relay fault, if you have had it recharged properly you most likely have a pin hole in the condenser unit or the radiator.

Steve.

When you say recharged properly what do you mean by this? Both mechanics connected the car with ac machine, did vacuum etc.. i mean the machine does everything right? They also performed a leak test, seems all good. Would it still be a leak?

 

also the relay fault… just had a search online would the fuse be position 29? Clutch sensor? Check this link;

https://www.servicetutorials.com/2021/11/30/audi-a3-s3-8v-2013-2020-fuse-box-and-relay-panel-location-and-diagram-explanation/
 

 

 

 

12 hours ago, Unique said:

When you say recharged properly what do you mean by this? Both mechanics connected the car with ac machine, did vacuum etc.. i mean the machine does everything right? They also performed a leak test, seems all good. Would it still be a leak?

 

also the relay fault… just had a search online would the fuse be position 29? Clutch sensor? Check this link;

https://www.servicetutorials.com/2021/11/30/audi-a3-s3-8v-2013-2020-fuse-box-and-relay-panel-location-and-diagram-explanation/
 

 

 

 

Hi the machine does indeed check for leaks via pressure But my A6 showed no leaks but at six weeks after it was done I was only getting cool air not cold so I dye tested the radiator and sure enough there was a tiny weep in the top right corner which was letting out very slowly so I had to replace the rad which was about £110 that cured it, if you look at the way the system is designed its a closed circuit therefore no gas should escape it only deteriorates after time and become weaker and wont do what it is supposed to because its full of contaminants, if you get it checked and there is no gas you have a leak, as for it running the pump all the time these systems activate via the relay which is why I suggested that, could be if the pressure sensor is feeling not enough gas pressure it is throwing it on to drive.

Steve.

On 9/30/2025 at 11:02 AM, Stevey Y said:

Hi the machine does indeed check for leaks via pressure But my A6 showed no leaks but at six weeks after it was done I was only getting cool air not cold so I dye tested the radiator and sure enough there was a tiny weep in the top right corner which was letting out very slowly so I had to replace the rad which was about £110 that cured it, if you look at the way the system is designed its a closed circuit therefore no gas should escape it only deteriorates after time and become weaker and wont do what it is supposed to because its full of contaminants, if you get it checked and there is no gas you have a leak, as for it running the pump all the time these systems activate via the relay which is why I suggested that, could be if the pressure sensor is feeling not enough gas pressure it is throwing it on to drive.

Steve.

Update.

I read online that it could be a faulty ac pressure sensor so I’ve replaced that, ac clutch still engaged and plate still turning with the pulley..

today i’ve decided to disconnect the electrical connector of the ac compressor expecting the ac clutch to stop spinning but it didn’t.

now i’m stuck, has the ac compressor clutch seized up? Does low ac refrigerant cause the ac clutch to always be engaged?

Will need to find a garage to do a dye test soon

also can you point to the right direction to where I can locate this relay? I’ve got a Audi S3 2018 8V…

 

Thanks

21 hours ago, Unique said:

Update.

I read online that it could be a faulty ac pressure sensor so I’ve replaced that, ac clutch still engaged and plate still turning with the pulley..

today i’ve decided to disconnect the electrical connector of the ac compressor expecting the ac clutch to stop spinning but it didn’t.

now i’m stuck, has the ac compressor clutch seized up? Does low ac refrigerant cause the ac clutch to always be engaged?

Will need to find a garage to do a dye test soon

also can you point to the right direction to where I can locate this relay? I’ve got a Audi S3 2018 8V…

 

Thanks

Hi if you replaced the pressure sensor chances are all the gas has escaped.

Steve.

On 10/8/2025 at 6:32 PM, Stevey Y said:

Hi if you replaced the pressure sensor chances are all the gas has escaped.

Steve.

Hi, upon releasing the pressure sensor, only small air managed to escape. A split second.

so upon disconnecting the ac compressor i can say the car drives 10x better, almost 100% if I’m honest. I believe previously the car was driving as if the AC was constantly on / under load.

Will need to replace the compressor before summer. 
 

Thank you