We can list many reasons why new air conditioning system installation must be left to professionals. One of them is only experienced HVAC technicians can do the calculations necessary for proper new cooling unit sizing.
What does sizing mean? It sounds like the technicians are taking measuring tape to find out how large the AC can be so it will fit into the space available. Which does sound a touch silly. Of course, a new air conditioner must be the right size to fit in a house, but why hire professionals for a job anybody with measuring tape could do just as well?