This called old school troubleshooting. You will literally have to follow the main power wires out of the ac and track their path.
Sometimes you find a disconnect in the rafters in basement...maybe none(not code)...the end result is you will have to physically follow them to find where power originates.
It is not the unit...it is the field wiring to the unit. Is there not a rectangle box on the side of the unit with a door that opens?
Fuses or breaker inside?
If not it was installed against code.
Then I can only guess that the unit was wired with a direct feed from the box.
I encourage you to be very cautious...this is not a safe situation.