I need to replace the A/Ccompressor on my 2.0Tdi PD Octavia. Could someone give me a step by step guide please.

First question is why?

If it has failed for example the solenoid has broken up inside (common) then the system needs to be flushed as there will be metal fragments inside. If these aren't cleaned out the new compressor won't last long. The dryer should also be changed at the same time.

Also any degassing and recharging now by law has to be carried out by a certified engineer.

Apart from the legal aspect, you have to appreciate that this sort of work requires access to a fair bit of specialised kit. Unless you have access to vacuum pump, A/C manifold, inert gas for flushing etc etc you are likely to be unsuccessful in your DIY attempt.

I have an air con guy who will be doing the work, but I am trying to gauge the time it will take (therefore the price of the job). I have a leak from the compressor and the high pressure hose out of the compressor needs its O-ring replaced

Compressor R&R is approx 1 hour. The O-ring will be part of this. Vac down and recharge is approx 30mins. If the receiver/dryer is also changed then add another 30 mins. HTH.

The air con guy thinks the alternator will need to come off to get to the compressor to though, so thinks a 3-4 yr job to have the air con up and running again