How to set up a/c and heat

As far as I know, every heat/ac unit has a vacuum operated valve in a heater hose that stops hot water flow through the heater core when in ac mode. I'm going to assume this aftermarket unit has a vacuum tube to be routed to that valve. If your vehicle never had ac you would need to purchase and ad the valve.
If by chance this unit has no vacuum operated features or vacuum required, you'll need a cable operated valve.