Air conditioning and plumbing contractors are well aware that p-traps in condensate drain systems are subject to frequent failures. You have witnessed the severe water damage and contamination to air conditioning units and the damage to surrounding property caused by these failures. The seriousness of these failures is not fully appreciated by many in the air conditioning industry. However, the fact that this situation is real is supported by the following assessment by ASHRAE [American Society of Heating, Refrigerating and Air Conditioning Engineers] Standard 62-89R, paragraph 5.6.4, which reads as follows:
"Condensate traps exhibit many failure modes that can impact on indoor air quality. Trap failures due to freeze-up, drying out, breakage, blockage, and/or improper installation can compromise the seal against air ingestion through the condensate drain line.
Traps with insufficient height between the inlet and outlet on draw-through systems can cause the drain to back-up when the fan is on, possibly causing drain pan overflow or water droplet carryover into the duct system. The resulting moist surfaces can become sources of biological contamination. Seasonal variations, such as very dry or cold weather, may adversely affect trap operation and condensate removal."
Despite this assessment of the condensate trap, it remains the choice of the industry as a means of drainage control. Your customers, the building owners and managers, suffer the consequences. Some of the many trap failure modes identified by ASHRAE are illustrated in Figure 1. These failure modes, which occur frequently, allow condensate blowing and flooding as illustrated—causing property damage and air contamination. Since all the air in a building passes through the air conditioning unit at a rate of several times per hour, the circulated health threatening pathogens inevitably expose occupants to degraded indoor air quality, as indicated in Figure 2.
Air conditioning and plumbing contractors usually have the responsibility for installing and/or maintaining condensate drain systems.