Why Is There a Puddle of Water Under My Car?

If you drive your car, run the air conditioning (AC), park it, and find a puddle of water underneath, it doesn’t mean your car is leaking fluid. The AC system has a drain tube to release moisture, but sometimes this tube can clog up and create problems like a wet carpet in your car. Find out more on why there’s a puddle of water under your car and a few other common questions about automotive ACs with this guide and video.

Why Is There a Puddle of Water Under My Car?

Mechanic reviewing why a puddle of water will be under the car and the cause, with a photo of an AC evaporator

What Is Causing a Puddle of Water Under My Car? Is It Normal?

You may notice a puddle of water forming under your car after you’ve run the AC, and you may wonder if it’s normal. The puddle of water is a common result of turning on and running the AC in your car. The AC system drains moisture off the evaporator.

What Is an Evaporator?

The evaporator is in the heater box. As refrigerant cycles throughout the AC system, it’s heated from a cool liquid state to a gaseous state. Air blows through the evaporator, and as the liquid is turned into a gas, cool air is blown into the cabin of your vehicle. While this process occurs, moisture forms on the evaporator and drips.

How Does the AC System Drain Water?

The heater box drains this moisture through a rubber tube, leaving a puddle of water under your car.

You might test this fluid and find it’s colorless and clear. You’ll know it’s water because of the lack of color and viscosity, unlike other fluids in your car.

Why Is the Carpet Wet in My Car?

If you find a wet carpet after running the AC, it doesn’t mean you have a big problem like the windshield leaking. Sometimes debris like pine needles from the vent area can clog up the drain and back-up the moisture to the interior of the car. Check the drain tube for any debris, and remove it with a small tool, like a small screwdriver.

Why Is My AC Not as Cold in Hotter Weather?

You might think your AC system needs a recharge if it doesn’t blow as cold in warmer temperatures.

The evaporator stays the same temperature. It also takes in air from outside that’s pushed into the cabin. That hot air from outside can push the internal temperature down, but the recirculating button will help you keep the cooler air inside your car.

Mechanic with an automotive thermometer
Automotive thermometer

You can find problems with the system by placing an automotive or meat thermometer in the vents. Then you’ll get a reading of the internal temperature of your car and compare it to outside. It’s normal for the internal temperature to only drop a few degrees if the outside raises somewhere around 15 to 20 degrees. If you find the internal temperature remains the same despite the outside temperature dropping over time, you’ll know you have a problem with the AC, like a leak.

Can I Drive with the Windows Down and the AC on?

The AC is a sealed system and doesn’t require a lot of maintenance to keep running, like having to add refrigerant. It’s not wasteful to run it while driving with the windows down. Driving with the windows down while the AC is on can give you poorer fuel mileage. The open windows can affect the aerodynamics and strain the engine.

Should I Recharge My AC?

You don’t need to add refrigerant to keep your AC working, so you don’t need to recharge it. In fact, we don’t recommend recharging the AC since it can cause more problems for your AC system long-term.

More on why you shouldn’t recharge the AC system in your car

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Why Is There a Puddle of Water Under My Car? - Expert Tips - 1A Auto
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Why Is There a Puddle of Water Under My Car? - Expert Tips - 1A Auto
If you see a puddle of water under your car and are wondering why it's there, learn all about it with the expert mechanics at 1A Auto with this article and video
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1A Auto
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