Yes it is. It indicates that the breaker is overheating. This can be the result of a few conditions. It might just be a weak breaker. It might be that you have the wrong breaker. The breaker lugs might be damaged. The AC unit might be overdrawing current. The first thing to do is to remove the breaker and examine the panel lugs. If you see any pitting or discoloration, you'll have to relocate a new replacement breaker somewhere else in the panel. (assuming you have the space for it). If the lugs look OK, just replace the breaker and see how that works. Normally, a central AC unit or heat pump requires a 50 amp 2 pole circuit breaker. But read the specs on your unit. Also, be sure the circuit breaker is rated for HVAC.
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