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Why Is There Water Around My Air Conditioner’s Outside Unit?


It’s a hot summer day and you’re out doing yardwork when you notice moisture on the concrete pad around your air conditioner’s outdoor unit. Or maybe it’s a puddle on the ground next to it. Either way, you may be wondering whether your AC is in trouble. There are actually several reasons why your AC’s outside unit might have water around it. Moisture can be a result of normal operations, but depending on the amount of water and how long it persists, it could also be a sign of a problem.

The outside unit of your air conditioner contains the condenser and compressor, while the inside unit contains the evaporating coils. When cold liquid refrigerant passes through the evaporating coils, it soaks up the heat from the air inside of your house. That causes the refrigerant to evaporate, or turn into gas, just like water turning to steam when you boil it on the stove. This hot gas travels through the compressor into the condenser, where the heat is released into the outside air as the refrigerant condenses back into a cold liquid, which travels through copper tubing back into the evaporating coils.

You know how a cold can of Coke will sweat on a humid summer day? The same thing can happen with those coils and copper tubes full of cold refrigerant. Humidity in the outside air can condense on them and drip off, leaving a small amount of moisture around your outside unit. When the unit turns off, this normal, small amount of moisture should quickly dry up.

Another way that normal operation can lead to water around the outside unit has to do with the drain line. Humidity from the inside air also condenses on the evaporator coils, drips down into a drain pan, and then drains out of the house through a drain line. If that line exits your house near the outside unit, it could be the source of the water around it. In this case, you simply need to look for the drain line—usually a PVC pipe—and see if there’s water dripping out of it, like there should be when your AC unit is running.

However, if there’s an excessive amount of moisture—so much that it doesn’t dry up quickly when the AC isn’t running—then there may be problems. Sometimes there are issues such as blockages or cracks in the drain pan or line. Other times, low air flow caused by a dirty air filter or dirty coils could be causing the evaporating coils to ice over. When the ice melts, a large amount of water will all come out at once, creating a puddle. Sometimes issues with the compressor or the reversing valve can cause it to sweat. A licensed HVAC technician can best diagnose the problem and find a solution.