Strange, Gurgling Sound from AC Condensate Drain

My AC is gurgling and it seems to be coming from these traps.

I loosened the clamps and pulled the pipes from the condensate pump (not shown in this photo) reservoir. I did this (while I was plumbing our new dehumidifier into the drain pump) because I assumed the pipe was gurgling when its outlet was below the level of water in the pump’s reservoir. However, that wasn’t the case and I narrowed-it-down to coming from one of those “traps” (the upper one).

I also noticed there’s a fair bit of air-flow coming from that pipe, too. I could stop it with my hand, so there wasn’t a lot of force/pressure, but there was a significant about of flow.

Soooooo, the (what I consider) excessive air flow from that pipe has me concerned. Should it?

Also, what are the traps for? What harm would I be doing to eliminate the noisy one?

One drain pipe, the lower one, goes to your household plumbing.
The upper one goes to the outside of the wall, but doesn’t ordinarily carry water, its there as a backup. The air flow is ordinary wind from the outside. Maybe strong wind is making the noise in it ?
So if the lower one blocks, the water level rises but drains through the upper one and doesn’t flood the inside of your house.

It may be that the noise is the air conditioner operating in the higher level of water is making the noise. Or perhaps the problem with the household plumbing is making the noise. (air vents must not be blocked just as much as the downward pipes need to be clear.)

Thanks for the info, Isilder. I’m with you; the lower one is the primary and the upper one is the “overflow” pipe to take over if the primary ever gets clogged.

However, I’m sure that both of the pipes are draining to the same place. They are both plumbed to dump into the condensate pump on the floor (can post a pic later today). The AC’s located in the basement (way below the house’s plumbing) and the pump lifts the AC’s condensed moisture up about 6 feet and through the wall to a (~7-feet long) pvc drain pipe outside. The pump outlet has a check valve that keeps the exit line full of water. There is no air coming through it.

To summarize:
What is the advantage to having the trap? I’m contemplating removing it so that the water doesn’t gurgle in there.

Should there be so much airflow in that pipe anyway?

In a commercial building, the main condensate drain might be dumped in a mop sink inside of a janitor’s closet. Another drain was protruding out of a ceiling tile over a lavatory in the restroom. If the main drain clogged up, the other drain was in a place where the dripping would be likely to be noticed.

In commercial coolers and freezers we use traps for a few reasons.
The force of the air going across the coils can suck air in through the drain. That brings in outside air that needs to be cooled. Often times it’s outside air which is not only room temperature but can actually be hot and humid. So more heat and more moisture that needs to be removed from the system. Also, it can bring bugs, dust and whatever else is outside (exhaust from an idling car etc).
Another problem that you can run into is that since you have the constant force of the air coming in, it can make it difficult for water to get out and this can cause it to overflow into the the cooler/freezer and cause other problems.
There’s a few other things I’m not thinking of off the top of my head and none of them really apply to a residential AC, especially in your situation. If you ever need to replumb it, there’s no harm in getting rid of the trap if you need to.

The gurgling, as you’re suspecting, is just a little bit of water in the trap bouncing around. My guess, if you never noticed it before is that the trap is running dry (did you bend it down a bit when you were monkeying around with the pipes?). It’ll probably stop the next time the AC kicks on and it fills back up.
If the outlet of one is higher than the other and that one is the problem, take the lower one and twist it up a bit (turn it clockwise) for a few minutes so it ‘overflows’ into the other one and the trap should fill back up that way.

Also, make sure the filter is clean (or you don’t have a bunch in intakes closed/block). If you’re starving the system for air, it’s going to look for other places to get it from.

In this case, the evaporator coil is downstream of the fan and under positive pressure, so the purpose of the trap is to stop cool air from blowing out the pipe. Same principle that Joey P described, just that it will blow air out instead of sucking it in. And since that looks like a condensing furnace, there should be a condensate drain for the furnace section too. I’m guessing it’s on the other side of the furnace?

Edit: I’m only right about the pressure if this is an updraft furnace.