The air handler is a vertical install, on a stand, with free air return, in a closet equipped with louver bi-fold doors. The install is about 4-years old. The owner is using 1" thick pleated filters, installed in the air handler filter rack (not in the stand rack); he is also using Web-brand filters behind the face of all supply grills. I first answered a "water leaking from air handler" complaint a couple of days ago, but the customer has now called stating the air handler is, again, leaking water... the water leak is from the right hand side, about half-way back from the lower edge of the cabinet. The condensate safety switch is installed correctly, with the switch chamber residing lower than the air handler overflow outlet; the system is NOT collecting water in the switch chamber. During the first service, I cut the drain line adjacent to the air handler and wet vacuumed in both directions (towards the air handler and towards the drain outlet... the drain is absolutely clear. I'm going back later today to recheck everything; I'll be pulling the male adaptor, from the AH main drain outlet, to verify no buildup at pan outlet; I will also recheck the leveling of the air handler; look from underneath for a cracked pan, and re-verifying there is no double-trapping going on (there IS a P-Trap correctly installed). I'm wondering if the owner's handy-dandy grill outlet filters can be messing with the static pressure within the air handler, thus preventing proper drainage. Other ideas?