AC Primary drain vent

[imported_John Smith]

I have seen several of these lately with tape over the open end. Sorry I dont have a picture, but try to envision the small vertical vent pipe (~ 6" in length) next to the evaporator coil. I skimmed the IRC, but didnt see anything about it.

[Jerry Peck]

Vent should be on opposite side of trap from AHU.

If not, it only serves as a clean out, and allows air to be sucked in or blown out, wasting energy (and, if sucking in, sucks in unfiltered air).

[imported_John Smith]

Yes, the vent is downstream of the trap. Im starting to question my understanding of this. I thought the vent was supposed to be open and not taped over or capped. I havent missed some new rule or change in physics have I?

[Jerry Peck]

Yes, the vent is downstream of the trap. Im starting to question my understanding of this. I thought the vent was supposed to be open and not taped over or capped. I havent missed some new rule or change in physics have I?

If it is downstream of the trap, it could be a vent, and would be open.

If it is upstream of the trap, it could be a cleanout access, and would be capped.