The NEC rules on A/C units are different.
If the nameplate says use a 70 to 80 amp breaker, then put that size breaker in the panel.
It may also say what the load is, and the conductors must be sized for that load. They may be larger.
In the special case of A/C and heat pumps the high starting loads can require the larger breaker, and the unit may be protected by slow-blow fuses that are smaller.
I'm away from my code so can't cite sections for you.