Art wrote:

That sounds normal. A system that is too large for a house will turn on,
cool the house quickly and turn off quickly. Every turn on and turn off
shortens the life time of an ac. In a perfect world it would be sized to
run forever keeping the house at the right temperature and never turn off.
Of course the outside temperature is always changing so that a perfectly
sized ac system is impossible to design. That is why they have multistage
systems. ...

Actually, while you are right that the reason for multistage systems
is so that the AC does not turn on and off as often, the major reason
that this cycling is undesirable is not AC lifetime, but energy efficiency
and humidity control.

When the AC turns on, you are spending energy for a while cooling down
you evaporator, ducts, etc. before you get to full efficiency. When you
turn on and turn off, you are blowing previously condensed moisture back
into your home.