Why does the car drip a lot of water when the air conditioner is on?
3 Answers
Here are the reasons why a car drips water when the air conditioner is turned on: 1. Evaporator: Because the car's air conditioning system is equipped with an evaporator on the dashboard, when the air conditioner is turned on (the AC key is activated), the surface temperature of the evaporator becomes very low. The moisture in the hot air inside the car condenses on the heat-absorbing fins of the evaporator, and the water droplets are collected by the plastic casing of the evaporator and discharged out of the car through a pipe. If the car has been parked for a while, sometimes the ground is clean with transparent water. Please don't worry about a car malfunction, as the engine coolant is usually antifreeze (green, red, or blue). 2. Condensation: Outside the compressor (low-pressure area) in the engine compartment, the condensed moisture from the air can also fall to the ground (sometimes the amount of water is greater than the drainage from the evaporator). 3. Water droplets: If the low-pressure pipe is not covered with insulating foam, moisture in the air can easily condense on the surface of the pipe, and the water droplets usually accumulate at the lowest point of the pipe.
It's actually quite normal for a car to drip a lot of water when the air conditioning is on, similar to how water droplets form behind a refrigerator. When the air conditioning cools, it gets cold, and the humid air inside the car condenses into water droplets when it hits the cold evaporator. This water flows out through a dedicated drain tube to the underside of the car, which is why you often see wet spots on the ground when parking in summer. If the humidity is particularly high recently or the air conditioning is used for a long time, the dripping can increase. However, it's important to ensure the drain tube isn't blocked—if leaves or small insects get in, water can accumulate. Last time, my drain tube was blocked, and the passenger footwell was soaked. If you're unsure, just bend down and check if water is dripping from the middle underside of the car; if it's draining normally, there's no problem.
My hometown is in the southern coastal area, and when I turn on the car's AC in summer, it looks like water is leaking underneath the car. At first, it really startled me. Actually, the principle is straightforward: the moisture in the hot air condenses when it meets the cold, just like water droplets forming on the surface of a cold soda can taken out of the fridge. The more humid the weather, the more water drips. I remember once during the rainy season, after driving on the highway for three hours straight, water was pouring out from the chassis when I parked at a rest area. But this is a normal drainage mechanism. In fact, if the AC doesn’t drip water, that’s when you should worry—it might mean the cooling unit is broken or the pipes are clogged. The drainage outlet is usually located near the chassis behind the engine. Just use a wire to clear any blockages—it’s really simple.
