Why does water drip from under the car when the air conditioning is on?

[SabrinaAnn]

Because the car's air conditioning system is equipped with an evaporator inside the dashboard. When the air conditioning is turned on (A/C button ON), 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 housing of the evaporator and drained out of the car through a pipe. The functions of the air conditioning system are as follows: 1. The air conditioner can control the temperature inside the cabin, heating or cooling the air to maintain a comfortable level; 2. The air conditioner can remove moisture from the air. Dry air absorbs sweat from the body, creating a more comfortable environment; 3. The air conditioner can intake fresh air, providing ventilation; 4. The air conditioner can filter the air, removing dust and pollen.

[AngelinaMarie]

That day, I had the car air conditioning on, and there was a constant dripping sound of water underneath. I thought something was wrong and nervously rushed to the repair shop to ask. The mechanic laughed and said it's perfectly normal—the air conditioning works like a refrigerator; when cooling, it absorbs the hot air inside the car, and the moisture turns into water droplets that gather on the evaporator and drain out through a tube. In summer, when humidity is high, the water is more noticeable, especially after being stuck in traffic or driving on the highway. If water leaks into the car and the carpet gets wet, that’s when there’s a real problem—it might be due to leaves or debris clogging the drain pipe, which needs to be cleared immediately to prevent mold and odors. I’ve been driving for ten years, and I remember one time I forgot to check, almost damaging the wiring. Since then, I’ve made sure to clean the drain outlets during regular maintenance—don’t make a big deal out of it, but saving money is important.

[OKai]

After turning on the car's air conditioning, I noticed water dripping underneath the car and was initially puzzled. After checking the car manual, I understood the principle. During air conditioning operation, moisture in the air condenses on the cooling components, much like condensation on a window, and then flows out through a small tube. Especially when driving in hot weather with high humidity, the amount of water increases. This is not a malfunction but a normal operation of the system. However, if the puddle on the ground is too large or water starts seeping into the car, it's time to pay attention—the drain pipe might be clogged with dirt, affecting the air conditioning's efficiency and increasing fuel consumption. I shared this interesting fact with my kids to teach them a little knowledge and develop the habit of checking under the car after driving to prevent small issues from turning into major repairs.

[VanBenjamin]

As someone who dabbles in simple mechanics, car air conditioning dripping is a normal result of condensation. During cooling, the evaporator's temperature drops, causing moisture in the air to condense and drain out through the bottom tube. Most cars operate this way, with the amount of water varying greatly depending on the weather—dripping faster when humidity is high. If the dripping is abnormal or water leaks inside the car, it might indicate a clogged drain tube that needs clearing. You can handle this yourself with a simple clean-up; no need to rush to a repair shop immediately. Just remember to perform regular maintenance to prevent long-term blockages that could damage the AC system.