air handler backing up water

People,

AC was still blowing cold when the water started dripping through the ceiling. water pan under the handler was full of water. Overflowing a bit of course, and soaking the ceiling below it (it is above our office).

I couldnt believe it as I routinely suck out the drain tube annually to clear the pvc drain. Just did it last month, but the tubing still clogged and pan started to fill up/overflow.

I sucked out the 25 gallons of water with a wet vac. Then, I thought why didnt the low voltage overflow switch stop /switch off the entire ac system? Then I pulled up on the switch lever while the system was on/blowing cold and nothing happened. So now I have 2 things wrong- why the flooding when I sucked out the drain tube and also probably a bad overflow stop switch.

Thinking to open the side panel, add bleach, and have it kill all the mold. Also, do you think I definitely have a bad switch and just need to replace it? What do they call those?

Thanks, people.