Well glad you fixed your issue.......but I am not sure how replacing a 120VAC breaker would fix your furnace fan (12vdc) from always running?
Probably the reason why your air conditioner was not working when the external power switch was off inside the furnace is because the furnace usually supplies 12vdc to the thermostat which uses that voltage to control calls for heat and cooling. So “switch off” inside furnace should result in no call for heat or cooling via the thermostat.
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