I turn on the air conditioner an after 20 minutes it begins to leak water from the back of the unit. The water is leaking from the top section of the unit.

The drain for the condensation is likely clogged
Sometimes you can separate the 3/4" PVC, connect a short piece of 3/4 Smurf(ENT), or a 3/4" sweep and Blow through the pipe, Add more water and blow that through, then pour bleach down the pipe a couple of times, reconnect, Good to add Bleach every so often.