This leads to to a lot of speculation and comments that begin with comments "If the AC was part of the original installation ........... etc. The waste of a lot of time and maybe further confusion for the original poster; some of whom shouldn't be 'at' electrics at all. I have a neighbour like that who could be dangerous!
A recent example here has been that 90 amp breaker question!
We still don't know whether the AC breaker worked fine for years and then started to trip? Is the AC unit itself working OK anyway, what other load is on that breaker panel etc. etc.
In other words incomplete information. No specifications or conditions under which things are being used.
Often when investigating electrical problems 'unusual' things have been found that threw a whole new light on the problem as originally perceives.
For example, 1) 3 way switches wired up for years so that "Oh yes both switches have to be on for the light to come on!!!!!". Someone had replaced one of the switches incorrectly. 2) A 230 volt motor hooked up to 115 volts! Didn't work well; got got and occasionally stalled! 3) An outlet on a computer desk designed for a light load or minor computer accessory into which some had plugged an extension cord for a kettle (1300 watts) and a toaster (1200) watts; all on one phase of a 3 phase supply. Which finally blew, when the computer area had to be powered by a 3 phase battery fed inverter not the mains supply! The massive unbalance shut down the whole thing and destroyed computer controlled telephone services for quite a while! 4) A grossly overloaded 230 b volt 3 phase delta supply, where someone had provided a centre tap on one of the phases of the supply transformer in order to get a zero voltage neutral; sort of. The voltage from that centre tap to the 3rd (other) phase was really weird!
While the above are generally some of the more unusual we had the same weirdness when one side of a neighbours 115-0-115 garage supply went open (outside) but their house was OK. Nobody could understand why they were getting c voltage on both 'sides' but the 230 volt stuff in the garage would not work. Answer switch off everything; but the handle of the main switch was broken off ............... and test the incoming voltages! So we actually had 115-0-nil! Better than a broken neutral probably!
Anyway gotta go. Neighbour has problem with electrical brake switch of his transport truck's air brakes! We think we've got it narrowed down but the most likely faulty switch is above and behind a hot Cummins diesel engine!