When My A/C Is On, There Is Water On The Floor by the Furnace

HVAC Function

• The air-cooling process in an HVAC unit works on a geothermal principle, as a liquid refrigerant changes the warmer air to water vapor. This occurs in the evaporator coil that is part of the furnace assembly in a “split” system indoor furnace, outdoor A/C unit, or is one of the components in a “package” system -- a single unit located outdoors. This water vapor returns to a liquid state when it passes through the A/C compressor, followed by the reliquefied refrigerant passing through the A/C condenser and back to the evaporator coil. Any malfunction along this line will cause water to appear around a furnace when the A/C is on.

Evaporator Coil Leakage

• The evaporator coil is located in the plenum, which directs the cooled air from the air-handling section of the unit through the duct system to the interior of the home. The tubing that carries the refrigerant back and forth between the A/C unit and the furnace naturally develops condensation during the cooling process. This tubing is wrapped with insulation to retain the condensation. Any area where the insulation has worn away or come apart allows condensation to drip down through the furnace to the floor. The coil may ice over at times, especially during frequent and continual use of the A/C unit. The plenum itself may develop condensation on the outside, which will eventually drip down the exterior of the furnace and collect on the floor as well.

Drainage Problems

• An HVAC unit must have some way to drain the condensation that collects on the inside of the unit. This generally consists of a system that includes a collection, or drip, pan and drain lines that route this excess water out to keep the entire HVAC unit dry, as it should be when working properly. Building codes require both a main drain line and a secondary drain, the latter connected to a different discharge system than the main drain line. Potential blockage of this drain system occurs in several places, including the drip pan drain and the drain lines, as well as the various fittings in the drainage system. This blockage may be the result of dirt and debris; clogged, bent, or improperly installed drain lines; and fittings that leak. Any of these malfunctions cause water to drip down to the floor around the furnace.

Prevention

• A clean air filter is critical for an HVAC unit to operate properly. The filter should be changed once a month at a minimum. A clogged drip pan can be remedied temporarily by using a wet-dry vacuum or a sponge and a bucket. However, the appearance of water around the floor of your furnace when the A/C is on likely requires at least an inspection, if not repair, by a qualified and licensed HVAC contractor. They can handle maintenance and repair on the many electrical and plumbing components of an HVAC unit.