Can a Secondary Drain Be Capped Off in a Residential Air Conditioning Unit?

How Air Conditioners Operate

• Air conditioners work by removing humidity from the air. This causes the temperature to drop. The humidity is removed through the rapid expansion of coolant in the air conditioner evaporator coils. Once the coolant runs through the evaporator coils, it is circulated back to the compressor, which returns the coolant to a liquid state. The coolant then begins the cycle again.

Air Conditioner Drain Pans

• As the air conditioner removes humidity from the air, the humidity condenses into water. The water winds up in the drain pan located just beneath the air conditioner evaporator unit. From here, the water drains off into a drain line and to the exterior of the residence. The drain line is usually connected to the side of the drain pan through a coupling, with rubber seals in place to keep the connection watertight.

Drain Pan Overflows

• Two devices inside the drain pan help to keep the pan from flooding over in the event of a block in the drain. The first is a float switch. This switch connects to the power line for the air conditioner. When the water in the drain pan rises to a certain level, as it would, for example, during a clog, the float also rises and cuts off the power to the unit. The second backup device is the secondary drain. This is usually connected to another side of the drain pan and provides an extra way for water to drain if the primary drain becomes clogged.

Secondary Drain Capping

• Although the secondary drain may seem like it's unnecessary, this drain should never be capped. In many municipalities, a secondary drain may be a required part of air conditioner installation and capping it could put you in violation. Keep the drain opening free of debris so that it can drain freely in case it is needed.