Why is there water leaking under the car when the air conditioner is on?
3 Answers
Here are the specific reasons for water leaking under the car when the air conditioner is on: 1. Evaporator drainage: Because the car's air conditioning system has an evaporator installed inside the dashboard, when the air conditioner is turned on (A/C button ON), the surface temperature of the evaporator is very low. The moisture in the hot air inside the car will condense on the heat-absorbing fins of the evaporator, and the water droplets are collected by the plastic housing of the evaporator and drained out of the car through a pipe. 2. Compressor condensation: Sometimes, the exterior of the compressor (low-pressure area) installed in the engine compartment can condense moisture from the air, causing it to drip onto the ground. 3. Lack of insulation foam: If the low-pressure pipes are not wrapped with insulation foam, the surface of the pipes can easily condense moisture from the air, and water droplets often accumulate and drip from the lowest point of the pipes.
I've noticed many car owners see water leaking under their cars when the AC is on, which is actually quite normal. When the AC cools the air, moisture from the cabin condenses into water droplets on the evaporator and is drained outside through the drain tube, just like water dripping from the back of a fridge. This is especially noticeable in summer when humidity is high. If you check and find the leaking water is clear, odorless, and colorless, it's completely fine—it's actually a sign that the AC is working properly. However, be cautious if the water leaks excessively or starts dripping into the car, wetting the carpets, as this could indicate a clogged or damaged drain tube that needs cleaning or replacement. Occasionally check the drain outlet near the front wheels before turning on the AC to ensure it's not blocked by debris. While driving, there's no need to worry about this, but a quick check during maintenance can prevent future issues. A simple action for worry-free driving.
Air conditioner water leakage is sometimes caused by minor faults in the drainage system. A clogged drain pipe is the most common reason—accumulated dust or leaves can prevent water from draining and may even cause it to backflow into the car. When parked, check the location of the leak: Clear water leaking near the front wheels is usually harmless. However, if the liquid is oily, foul-smelling, or colored, it’s not from the AC—it could be coolant or another type of leak, requiring immediate repair. I recommend first trying a simple cleaning of the drain outlet, using a wire to unclog it or a blow dryer to clear it. If the AC hasn’t been cleaned for a long time, bacterial growth can contaminate the water, posing health risks. Don’t overlook this—regular maintenance of the filter and the entire system can significantly reduce leakage issues. Address problems early to prevent minor issues from escalating.
