Why is my A/C drain line not draining at all?
Take your shop vac outside and hook it up to the drain line to suck out whatever gunk is in the drain line. If that doesn't work, you can also use an air compressor at the air handler end of the drain line to push out the clog. Or get a helper and do both at the same time.

Once it's running clean, you'll want to flush out the drain line with some bleach. Mix a 1/4 cup of bleach in to 2 liters or a gallon of water, turn off the air handler, and pour the bleach water in to the drain. Let it sit for 15 minutes or so, and pour fresh water in to flush out the bleach.