What Causes Water Intrusion in Car Air Conditioning Systems?

[MacNathan]

Possible causes include improper unit installation or drainage pipe malfunctions. Below are relevant details: 1. Overview: A car air conditioning system refers to the climate control device installed in vehicles, capable of cooling, heating, ventilating, and purifying cabin air to provide passengers with a comfortable environment, reduce driver fatigue, and enhance driving safety. 2. Structure: Typically consists of refrigeration units, heating units, and ventilation systems. This integrated design maximizes limited vehicle space with simple structure and user-friendly operation, representing internationally prevalent modern automotive AC systems. 3. Configuration: Different AC system types feature varied layouts. Most modern passenger vehicles adopt combined heating/cooling systems, where components like evaporators, heater cores, centrifugal blowers, and control mechanisms are assembled into a single unit called the AC assembly.

[SanBrooke]

A while ago, my car's AC also got flooded, and it took me quite some time to figure out the issue. The main problem was a clogged AC drain pipe—leaves and mud blocked the water from draining, causing it to spill directly into the car through the AC vents. Also, using a high-pressure water jet to wash the car and carelessly spraying the AC intake can force water inside. Additionally, if the rubber seals under the car are worn out or the windshield isn’t sealed properly, heavy rain can seep in and soak the AC filter. In my case, the drain pipe was clogged, and the passenger-side floor mat was completely soaked. When I took it apart, I found the evaporator was already moldy. Later, clearing the drain pipe and replacing the filter cost me 200 RMB. I should’ve cleaned the leaf buildup in the engine bay more often.

[ManuelMarie]

As someone who repairs cars every day, I've seen plenty of cases of air conditioning systems getting flooded. The first culprit is usually a clogged drain pipe—that thin tube located under the passenger seat. Even a single leaf can block it completely. Another common issue is improperly installed or low-quality cabin air filters, which trap moisture in the ducts. Older cars with cracked sealing strips may let rainwater seep in through the fresh air intake, especially noticeable after summer downpours. The worst scenario is flood-damaged vehicles, where the entire AC system needs disassembly and drying. I recommend car owners check the drain pipe before the rainy season and avoid blasting the AC grille with high-pressure water jets during car washes.

[DianaDella]

Just dealt with this annoying issue last week. While driving, water suddenly dripped from the air vents, which gave me quite a scare. Upon careful inspection, I found the evaporator core was holding water. Normally, condensate water generated during AC operation should drain through the discharge tube. In my case, the plastic tube joint had come loose, causing all the water to leak into the cabin. Another time, I forgot to close the sunroof during a heavy rainstorm, and rainwater flowed into the AC system through the A-pillar. To make matters worse, I discovered the AC filter box sealing ring had aged, allowing car wash foam to seep in. Now I make it a habit to check the drain outlet under the car every month, especially since repairing the AC evaporator requires dismantling the entire dashboard.