Solus... not sure where you live, but on the west coast of Florida, the humidity is very high in the summer, and air conditioners may run 24/7 intermittently ...many Floridians have their air handler (squirrel cage blower fan) and evaporator core (where liquid refrigerant expands to a gas inside a closed tube core, this expansioin absorbs heat from surrounding air, and cools it.... this cooled air is pumped into the house by fan pressure... in doing so, the water vapor in the previously warm air is dropped below its dew point and becomes liquid water droplets... this water is collected below the air handler in a drip pan... typically a PVC drain line provides a release of this water... to protect the ceiling below the air handler, if this drain line should fail, there is a float switch that shuts off the system if the water approaches the top of the drip pan...a shop vac attached to the bottom of the drain line can un-plug the line, where typically mold has built up, clogging the line.. I have a yearly service that routinely cleans the line... it has been brutally hot the last couple of months, and the build up since the service in May caused a shut down Friday...I need to build a better adapter to attach my shop vac to the line.... Les