Why does a cooling system need a condensate drain?

Cooling removes both sensible heat and moisture. As indoor air passes across an evaporator coil operating below the air's dew point, water vapour condenses on the fins and runs off — a meaningful volume, gallons a day in humid conditions. The condensate drain exists solely to carry that water away to an approved location. Everything that goes wrong here follows from that being a continuous, unattended process: the drain line clogs with biological growth because it is constantly wet, the pan corrodes, the trap dries out or was never installed so the line will not flow against the blower's pressure, and the secondary pan's own drain blocks. The result is water where the equipment sits, which for an attic unit means the ceiling below and for a closet unit means the floor and adjacent finishes.

Air passing over a coil below its dew point gives up moisture, which condenses on the coil and must be drained away. The condensate system exists to carry that water to an approved termination.

Cooling coils condense moisture from indoor air, which is collected in a primary pan and carried away by a drain with a properly configured trap. Secondary pans and float switches protect against primary system failure.

Cooling Makes Water — gallons of it. The drain is not an accessory; it is where the by-product goes.

Check for a float safety switch, especially on attic units. Its absence means a blocked drain reaches the ceiling before anyone notices.

• •Confusing condensate with refrigerant
• •Overlooking a missing or dry condensate trap
• •Failing to check for a secondary pan and float switch