I think the air handler pipe that goes to the outside is clogged, can I use liquid draino in it to clean out the line?

The best way to clear this drain line is to blow it out from the air handler to the out side , you may have to cut the line to be able to blow it out, so you will have to couple it back together. Use compressed air or co2.
Be sure this line goes outside and not to the tail piece of a sink somewhere, if this is the case then lay a wet towel in the sink to keep from blowing STUFF out of the trap and into the room.
Also go outside and make sure the end of the drain is open and not plugged. I don't recommend Draino. Mike