What was wrong with the old compressor?

I'm not the most technical person even when it was explained, but the obvious issue was the bolt at the end by the pulley part was coming out. Making a horrid noise too before that was spotted. I thought it was the fan belt initially until I realised it wasn't blowing cold air.

 

I was told it is a common fault. 

Ahh probably the T30 torx on the end. That's the Denso compressor iirc. Good fault to get if you have to get one as the internals should be ok so you don't need a flush and if the repair is carried out in one remove and install operation there isn't a need to replace the drier.