We've got an attic AC unit. Over the past week the AC has shut down
(wonderful in our 90+ summer weather). It's doing this because of a
kill switch in the drip pan. As the drip pan fills up, it raises a
float on the switch and shuts the unit off.

By literally bailing the water out of the drip pan, we can get the AC
restarted. Of course this is not a practical solution.

From reading here, I believe the problem is caused by the primary drain
line being clogged? Can someone walk me through some steps to unclog
this line?

The system has two PVC pipes coming out of the attic unit. One takes a
short bend and opens into the drip pan, this is the one thats seeing
the action at the moment. The other line seems to run towards the side
of the house, presumably to connect with the drain line off of the
bathroom in that direction. This line has an opening at a Y joint near
the AC unit. One part of the Y continues to the drain line as
mentioned above and the other part of the Y is a short piece of pipe
open to the attic. Thanks in advance for any suggestions.