Heating, ventilation and air conditioning, or HVAC, units employ an evaporative cooling coil to remove moisture from the indoor air. If an HVAC unit is not maintained properly, water can leak into interior areas. Often a basic cleaning can eliminate the problem. Some leaks may take a trained technician to perform since the problem may be present as a severe clog to the condensate drain lines.
The Evaporative Coil
All HVAC units employ an evaporative coil that resides just in front of the central blower fan. The blower fan pulls air from the interior space and passes it across the cooling evaporative coil. As the air passes over the colder metal, moisture in the air will condense on the cooling fins. The collected water then drips down the fins and into a lower collection pan. From this pan the water is sent outdoors through a pipe. The pipe is typically orientated so it will gravity feed. In rare instances, the water must be pumped from the condensate pan and into a nearby drain.
The Condensate Drain Pipe
In most instances the condensate drain pipe will become clogged from environmental debris. This debris comes from the air in the form of dust and pollen. The particles can accumulate in the drain pipe and stop the flow of water. The water can then get to such a level below the evaporative coil that the blower fan will literally pick up the water and push it through the duct work.
It may be possible to blow out the clog from the drain pipe by using compressed air, but you might just blow the debris back up into the drain pan and later have it fall back down into the pipe. Using a wire drain snake may open the clog in the drain pipe as well. Be careful not to shove the wire snake too far into the unit so you don't damage the evaporative coil. If possible shut off the air handler unit and open the access panel to the drain pan. Use a garden hose and wash out the pan along with applying water pressure to the drain pipe. Generally this will clean out the condensate drain system. If you live in an area with heavy pollen in the spring you may have to perform this cleaning method each year to remove the debris.
Pumps and Severely Clogged Piping
HVAC units that employ a condensate pump may require the services of a licensed HVAC technician. In some cases the pump motor may have failed and needs to be replaced. Severely clogged pipes may have to be completely disassembled and then replaced. As most of the drain piping is made from PVC piping, this type of pipe is permanently glued together. Once the leak is located and removed, the PVC piping will have to be reinstalled and glued back into place so the water can gravity feed from the condensate pan. Many of these gravity feed drain pipes must also employ a type of air block or drain water trap so outside air does not enter the air handling unit. In most cases this water trap must be configured by the HVAC technician.