Why does my condenser keep running after a cooling cycle?

You could be right. General controls on a central heating and air would shut down the condenser upon disconnect of the "Y" terminal. You can check to see if there is control voltage to the condenser relay once you have disconnected it. If there is no power to the relay then something like a relay has locked it down and won't release until the cycle is completed.

That would mean there is a good chance it is a bad board OR a bad sensor. Being that I don't know how these part operate and what there normal position is I can't comment on how to test the components.

Hope this helps and good luck