My friend had his Gibson A/C air handler shut off on him this weekend due to a clogged condensate water drain pipe. Luckily it had a "Safe-T- Switch" so that the backed up water in the drip pan didn't leak into the house.
I helped him unclog it and took pictures of the process. It should be a similar procedure for other air handler units from popular manufacturers like Trane, GE, Mars, Rheem and Carrier.
Here's the guide -
formatting link
I hope someone finds it to be useful.
Cheers, Paul