2008 audi a5 coupe 3.0 tdi ac compressor won't engage

Hi guys, I have a 2008 audi a5 coupe 3.0 tdi on about 138k miles, the ac was blowing ice cold on 1 side and slightly warmer on the other, it was like this for a couple weeks but then eventually stopped blowing cold at all so I thought it was just a case of getting it regassed, I took it to 2 different places to get it regassed but both said that no matter what they couldn't get the compressor to engage/kick in.. they said it could be a sensor, a switch or the compressor itself.. so I've now taken it to a 3rd place for a diagnosis and they said they think it's the compressor but to test the compressor they have to basically get to a point where they start taking it off to get to the plug so I might aswell just replace it while they're at it since they think that's the problem anyway.. what do u guys think? I've scanned the car using obdeleven and got the car scanned by them and it's got no codes at all