I had a '92 parts car to do the swap in my '87, so I used the condenser fan, all of the plumbing, the accumulator, the evaporator and the inside section of the console, as well as the passenger side firewall plate, all of the wiring harnesses, relays, pressure switches and control switch from the donor car. I had to buy a new condenser because the old one was destroyed. You need all of those parts plus a wiring diagram for each car to make the proper connections. The biggest wiring challenge was finding the proper wire from the newer harness to make the connection to the proper pin on the ignition control computer behind the dashboard to raise the idle speed when the a/c system is on. I left the original harness in place and tapped off of it for power. The A/C harness is a "free standing" harness, it's not integrated with any of the other systems in the car except the ignition computer, which makes the installation easier. You basically run the harness from one component to another, plug it all in, give it power, connect it to the ignition computer, and it should work.
The later model evaporator is larger, so the newer console was shortened by Volvo to accept it. While you're in there, do the heater core, heater hoses, blower motor and resistor, because you won't want to go back to do that later. The only part I kept from the original car was the compressor, which looked new, and the hoses from the compressor to the accumulator. There are some pic in my signature.
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