Need someone with hands on experience replacing AC compressor in 850 Turbo. What will have to be removed / disconnected to access? What other parts should be replaced at same time (such as drier?)? Any pitfalls to be wary of? Grateful for any experienced input.

I'll tell you after the weekend when I've done mine!! Mines packed up

It looks quite straight forward.

De-gas system (properly!) - remove drive belt - disconnect wiring - remove the 2 pipes on rear of compressor - remove bolts holding compressor in place. No need to adjust on replacement.

You could replace the 1 'O' ring per pipe on the rear of the compressor. The 2 pipes are tightened to 24 Nm

The compressor mounting bolts I think are 40 Nm

If you replace the drier, the nut connectoin is 30Nm, and the other connection you'll need a special tool to remove (see Snap-on, R12 service tools) There are 2 'O' rings per pipe. I didnt replace any of the 'O' rings when I changed my evaporator and drier - Volvo ordered the wrong ones, and anyway the techs at Volvo said no need to change................

If you've not had the drier changed, and/or it's been on more than 2 years, change it. They're quite cheap (compared to a compressor or a compressor!!! Or professional re-gas for that matter)