Phoenix Home Inspection

The condensate line on an air conditioner requires a p-trap.  The p-trap stays wet all the time.  The water in the p-trap keeps any contaminants in the attic air from entering the system and getting blown into the house.  The vent allows any contaminants in the line to escape.  It is important to install the vent after the p-trap.  Contractors may tell you that the vent is before the p-rap so that the home owner can pour some bleach in it periodically to keep the line flowing freely.  That is fine to do as long as the vent has a cap on it and there is an open vent on the other side of the p-trap.  The vent in the picture will allow the air blowing across the coils to blow into the attic and waste energy.