I need to run a 220 volt line from the main panel inside the house to the back yard and terminate into a switch disconnect for a split AC.

My main panel does not have a main breaker and there is only (1) slot available for a 110V breaker, so I thought tapping a sub panel ( switch disconnect with a 30 amp 220V breaker) would do the job.

I need some advise on how to do this. My plan is to tap the line for the sub panel to the incoming 220volt at the main panel and run the wire to the back yard to the sub panel (switch disconnect). This is a condo in the West LA area.