I did the V5 & R134a conversion in my Fiero several years ago. It was a fair amount of work. Here's a brief list of what's involved:
1) Modify compressor mounts to fit the V5
2) Swap V-belt pulley onto V5 compressor (requires a special tool)
3) Replace receiver/dryer unit and orifice tube with R134a compatible parts
4) Replace all the seals in the A/C system with R134a compatible seals
5) Modify engine wiring harness to accommodate the V5 compressor
6) Have custom compressor hoses made to fit the V5 compressor
On the DA6/HR6 compressor, you have 3 separate switches controlling the system: a low pressure cycling switch on the receiver/dryer, a high pressure cut-off switch on the compressor, and a fan switch on the compressor.
On the V5 setup, there are two switches (high and low pressure). Both switches are on the compressor. So the wiring for the cycling switch needs to be re-routed back to the compressor. And both switches on the V5 get wired into the cycling switch circuit.
Also, the V5 compressor doesn't have a fan switch, because it was used in cars with ECM controlled radiator fans. The V6 ECM can't control the radiator fan. So you have to rig something up. I used the low-pressure switch to double as the fan switch; it activated a relay which would ground the fan switch wire.
The high pressure cut-off switch on the DA6/HR6 compressor is wired into the ground leg of the compressor clutch. The V5 compressor doesn't do that (the high-pressure cutoff is part of the cycling switch circuit). The cut-off switch wiring needs to be deleted, so the clutch is grounded at all times.
Also, the suction and discharge ports on the V5 compressor are opposite from the DA6/HR6 compressor. And the compressor itself is a different size/shape, with the ports in a different location. So custom compressor hoses need to be made, to account for that. Neither the stock V6 nor 4cyl compressor hose assemblies will fit, due to interference issues.
Sounds like fun, doesn't it?
[This message has been edited by Blacktree (edited 07-08-2014).]