Can you use a smaller breaker than the maximum on an AC nameplate?
Yes, you can go smaller than the marked maximum. The two numbers on an air conditioning nameplate do different jobs. The minimum circuit ampacity, or MCA, sets the smallest conductor you may install. The maximum overcurrent protective device, or MOCP, sets the largest breaker or fuse you may install. Nothing in the NEC says you have to use the maximum. Section 440.4(B) requires the equipment to be marked with both, and 440.22(A) requires the branch circuit short circuit and ground fault protective device to be capable of carrying the starting current of the equipment.
Working the example
MCA 32 amps means the conductors must have an allowable ampacity of at least 32 amps. Ten AWG copper THWN-2 is 35 amps in the 75 degree C column of Table 310.16, so 10 AWG copper satisfies it, and 440.32 supports sizing conductors from the manufacturer marked MCA rather than recalculating from the compressor rated load current. The MOCP of 50 amps means you may not install a device larger than 50 amps. Between those two numbers, a 35, 40, 45 or 50 amp device is all legal on paper.
What the practical floor is
Do not drop below the MCA. A 30 amp breaker on a unit with a 32 amp MCA is protecting at less than the required conductor ampacity and will be called on inspection. Start at 35 amps and work up. The real constraint is locked rotor current: 440.22(A) requires the device to carry the starting current, and a hermetic compressor pulls five to eight times its running current for the first fraction of a second. That is exactly why the manufacturer put a 50 amp ceiling on a unit that only needs 32 amps of conductor. If a 35 amp breaker nuisance trips on start, go up, all the way to the marked 50 if needed, without changing the conductors.
Use an HACR rated device
Section 440.22(C) and the marking requirements in 440.4(B) mean the device must be of the type the equipment is listed for. Most residential and light commercial condensers are marked "maximum HACR type circuit breaker," and molded case breakers from the major manufacturers carry that HACR rating today. Fuses are the other permitted choice where the nameplate says maximum fuse size, and a fused disconnect at the unit is common in commercial work.
Do not forget the outdoor GFCI rule
Section 210.8(F) in NEC 2023 requires GFCI protection for outdoor outlets supplying certain equipment rated 150 volts or less to ground and 60 amps or less, which catches many residential condensing units. Check whether your jurisdiction has amended that section, because several states have delayed or modified it after nuisance tripping complaints on inverter driven equipment.
Field takeaway
Conductors at or above the 32 amp MCA, device anywhere from that value up to the 50 amp marked maximum, HACR rated, and size up rather than down if the unit trips on start.