A/C compressor not kicking on

[Moffett]

What's up everyone, so a last week I noticed that my a/c wasn't blowing any cold air. I have started going down the list of what it could be, I checked the refrigerant and it was good. I then checked all the fuses and none are blown. I crawled under the car yesterday and serpentine belt is spinning along everything fine (not a pulley anywhere clocked up). I did notice that the compressor is not kicking on. So my next thought is maybe the relay is bad.... and now that is where I'm stuck.

Does anyone know where the relay is for the a/c?? I have found a few different documents but nothing for the b8 s4. I heard that the horn relay is the same voltage as the a/c. I found the horn relay but not sure which relay to switch it with to check if the a/c relay is bad.
Any help would be greatly appreciated, service manual, diagrams, or even where to just look. I am down for paying for service manual if someone knows where to point me for one that is actually specific to the car.

Thanks!!

[ezridah]

Behavior is similar to when my thermostat went bad although the period of time between the AC started blowing warm air and the check engine light coming on was fairly short. Pretty common issue on the B8 S5 around 50k from what I read but not sure if same for your car...

[wilazn]

Check your AC pressure switch. Located in the front by the drill on the driver side. Same thing happened to me. Failinbg ones are a common problem.

Sent from my Pixel 2 XL using Tapatalk

[mys4.org]

Mine just went out over the weekend. I scanned it with my OBDEleven (https://www.ecstuning.com/b-obdeleven-parts/obdeleven-pro-scan-tool/024871obd01~a/#mys4.org) and it recommend the pressure switch. I got a new switch and A/C is back working.

Just so you know the A/C pressure switch is part number: 4H0959126B
https://www.fcpeuro.com/products/audi-vw-ac-pressure-switch-4h0959126a

You need a 24mm wrench/socket to get it off. It is in front of the radiator and A/C condenser below the black plastic cover. Is is on the driver side. I couldn't find any instruction online so hopefully this will help you out.

https://s3.amazonaws.com/uploads.hipchat.com/16105/63961/zKED5pRAeS1iB5C/upload.png
https://s3.amazonaws.com/uploads.hipchat.com/16105/63961/8eX9LabffM12tkE/upload.png

[Dr GP]

Also check the battery connections to make sure one of minor connectors(don't know the proper term) is not burnt through. Kind of like a fuse element but just metal strip