Alot of times, if there isnt alot of room in the attic for the proper "P" trap, installers will use a "J" trap. Depending on your unit, (electric airhandler or gas furnace), you might need a different kinda trap. The paperwork that came with the blower unit will tell you exactly what you need. Also, just because the unit in the attic is level doesn't mean it's correct. Plastic drain pans sometimes shift slightly, or the installers might have been a little rough getting the unit up in the attic and twisted the case a hair or the guy at the warehouse might have popped the side of the unit with his forklift when he was loading onto your installers truck. If unsure, pull the cover to the coil off, get a couple cups of water and experiment with the drain pan. You might find you need to shim one side or the other.

Don't get rid of the float switch. The secondary pan should have its own drain line that terminates in an obvious location that you can see if it's leaking.

Hope this helps

Sorry about the title of the thread. You have valid points. We reevaluated the level of the coils. There is an appropriate angle on the unit itself. The trap is shaped like a "V" then downstream is the vent. What purpose does the trap serve?
We cut the drain line just past the vent, removed the trap and vent, checked flow through that piece and the drain pipe. They flowed properly. We checked the drain through the coil housing. Good as well. It seems to work for an hour or so and then malfunctions. I reinstalled the trap and vent piece and placed a pan under it. The pan does have water in it.
I may have to go up there and just sit while it is operating.

The trap is basically just what it says... a trap. In this case it's to keep the back flow of odor from the drain system getting inside the airhandler. Again...depending on what type of unit you have, the trap also helps the water drain from the pan. If your airhandler has the blower downstream of the evaporator coil...meaning the air enters the coil 1st, then gets sucked into the blower housing and pushed into the ductsystem, then there is a small amount of negative air pressure in the middle of the coil and around the drain pan area. That negative pressure tends to hold back the water from draining untill the unit shuts off, then you get a flood of water trying to get out the drain. The properly sized "P" trap lets the water flow down the drain, insted of being held partially back in the pan.

I would make my "P" trap 5" on the long side and 2"-3" on the short side. Dont vent it at all after the trap or before it. Make sure the doors are on the air handler and if you want, cut a hole in the return air duct, get a flashlight and watch and see how it works. By watching where the air enters the unit, you are not changing the way the unit would work normally.

Hope this helps

sounds like you need a vent before the p-trap.