Hi, I am installing wiring for a new central air condenser that is being installed next week, and I wanted to make sure I was not missing anything. The HVAC installer told me that I needed #8 and 40 amps. I have a flexible whip to go from the disconnect to the condenser and have run (2) #8 wires plus a ground across my basement to the breaker box. I bought a 60 A disconnect box (is this the proper size? Only size Lowe's had) and it has an on/off switch rather than a pull out or a fuse style. Does the type matter? Inside this box I assume I hook up the wires from the circuit breaker to the line terminals and the wires from the condenser to the load terminals, is this correct? Finally I wasn’t quite sure which circuit breaker to buy, I know 40 amps and I’m pretty sure it’s a 2 pole, and hacr but other than that is there anything to the circuit breaker selection? Anything else I might need to know to keep this wiring job up to code would be helpful. Thank you.

Do not use a 60 amp breaker on #8 wire. You need to install a 40 amp breaker at your sourse [subpanel] then take that to a disconnect box. Depending on the area you are in, it can be fused or not. If it does have to be, then the fuses, or breaker needs to be 40 amps. The disconnect box needs to be next to the condenser unit. Hope this helps!

60 Amp Disconnect Enclosure OK. Use 40 amp breaker for protection at panel. Disconnect can be switch, pullout, and could use 60 Amp for Disconnect, Wires are already protected at panel. I would pull a pair of #12's with power to both units for compressor control wires.
After rereading your post, I notice you say compressor.Usually pair of #10's(30 Amp)for
Compressor Unit. Air Handler would be the 40 Amp.
If money not a major problem, I would pull #6's. Still 40 Amp breaker. Less loading down and ready for future upgrade.