Cassette Leaking After Heavy Rain: Drain Outlet Froze Briefly

• •Concern: Worry was that the unit had a cracked condensate pan or internal leak requiring expensive repairs
• •Key check: Checked drain during operation and observed frost forming at the outlet during heavy humidity periods

Water leaks tied to rain patterns suggested a drain issue, but the intermittent timing pointed elsewhere. We checked the drain path during humid operation.

• •Drain line itself was clear. No blockage.
• •Drain outlet was positioned directly below the cassette in the cold air discharge path.
• •During the diagnosis visit on a humid day, frost visibly formed at the outlet.
• •Frost formation coincided with peak condensate production from the indoor coil.

During heavy rain with high indoor humidity, the coil produces heavy condensate, and because the drain outlet sits in the cold air stream, it freezes briefly when flow peaks. The blockage lasts only minutes, but during continuous rain that is enough for backup to overflow the pan and drip from the edge.

The drain line and pan are fine, the problem is the outlet position. Moving it away from the cold air path gives condensate a warmer flow path, and the repositioning is straightforward.

The drain outlet was repositioned away from the direct cold air stream. During the next heavy rain two weeks later, no leaks occurred. The unit has remained dry through subsequent rainy periods without any further drainage issues.

Drain freezing is rare but specific to unit placement and humidity extremes.

• •A drain outlet sitting in the cold air stream freezes briefly during heavy condensate loads. Blocking flow for just a few minutes, but during heavy rain that is enough to cause overflow.
• •This diagnosis needs visible proof. A clear drain line, frost forming at the outlet during humid operation, and leak timing that follows heavy rain separate this from an ordinary clogged drain.
• •Moving the outlet away from the cold air path prevents freezing without affecting normal drainage.