Why Is My Air Conditioner Spitting or Leaking Water?

An air conditioner is basically a dehumidifier. It works by literally sucking heat out of the air to fuel the ongoing vaporization in its evaporation coils. As the air around the coils cools, the moisture in the air condenses on the coils to form droplets. From there, the water drips into a drainage pan and gets transferred outside or into the plumbing system through a network of pipes. When water starts spitting from the front of the unit, it often signifies a problem with the drainage system, but there are other reasons for this to happen.

Modern bedroom with air conditioner
credit: archideaphoto/iStock/GettyImages
When working properly, air conditioners drain water outside -- not inside.

Water Is Spitting Outside

If you notice water spitting from the outdoor side of your wall- or window-mounted air conditioner, don't worry -- it's normal. The circulation fan blade is fitted with a slinger ring that picks up water from the drain pan and slings it against the condenser coils. These coils get hot because the refrigerant inside is being compressed by the condenser prior to entering the evaporative coils. The spray of water from the slinger ring cools down the condenser coils, which in turn prevents the condenser from overheating. It isn't unusual for some of the water from the slinger ring to spit out from the back of the unit.

Water Is Spitting Inside

If you have a wall or window unit, water spitting outside may be normal, but water spitting inside the house isn't. Whether it's dripping from the bottom of the unit or actually flying through the air, it means something is wrong. Fortunately, you can often fix the problem yourself fairly easily.

Drainage System Blockage: When there is a blockage in the drainage system, water can't get outside or into the plumbing, so it collects in the pan, which eventually starts to overflow. The force generated by the circulation fan can throw some of this water into the air and force it out through the front grille, but usually the water just drips onto the floor. The remedy for this problem is to suck dust and dirt from the drainage hose using a wet/dry vacuum. Look for obstructions in the bottom of the drain pan itself, and remove them.

Cracked Drain Pan: When you see water dripping inside, the cause could be a corroded or cracked drain pan. You can sometimes fix cracks in plastic pans with epoxy glue, but corroded metal pans need to be replaced. It's also often easier to replace plastic pans than to try to repair them.

Improper Slope: Wall and window air conditioners are installed with a slight slope to the outside so that water will flow that way. If the unit slopes toward the inside because of improper installation or shifting, water can collect in the front of the drain pan and spill over. Check the slope with a level, and correct it if necessary.

Coil Freeze-Over: The evaporative coils can ice up, and when the ice melts, water may drip from the front of the unit, and again, the force of the fan may turn the drip into a spray. Coils ice up for these reasons:

  • The air filter is dirty. This reduces air circulation inside the cooling chamber. You should clean or change the filter at least once a month.
  • The refrigerant level is too low. This isn't something you can fix yourself. By law, a licensed air conditioner service technician must do it.
  • The temperature outside is too cold. Air conditioners aren't meant to be used in cold weather. Generally, if you use your air conditioner when the outside temperature is below 62 degrees Fahrenheit, the coils are likely to freeze.
  • Other mechanical problems are responsible. For example, the blower fan might not be working properly. If you've eliminated other causes for freeze-over, it's time to hire a pro to diagnose the problem.

Water Spitting From a Central Air System

A central cooling system works the same way as a window air conditioner, except that the coils, condenser and blower are located far from the cooling vents. Consequently, it's rare to see water spitting from a cool air vent, but you might see it dripping. If so, the reasons are often the same: clogged drain line, dirty air filter or low refrigerant charge. A dirty air filter and a low refrigerant charge can cause freeze-over, and melting water may overload the drain system.

There's a fourth reason for water to drip from cooling vents: insufficient duct insulation. The air inside the duct is cool, while the air outside it is warm. Moisture from the warm air can condense on the outside walls and seep toward the vent opening, from which it drips. Increasing the insulation on the outside of the vent prevents this from happening.

If water is spitting from a central air system's outside condenser unit, it's nothing to worry about. It's probably just the slinger ring, although it doesn't hurt to check for drain blockages. You should do this once a month as part of routine maintenance.