What is the cause of the AC unit leaking water?

The 1st thing you need to understand when your air conditioner is leaking is where the water is coming from. When the unit is working correctly, water condenses on the air conditioner's cooling coils, dribbles down into a collection pan, and then drains away down a pipe. You don't know the water's even there because you never see it.

If you do have a wall AC unit leaking water inside, the most likely cause is that the drain on the appliance's condensate drip pan, or the drain line, has gotten clogged. It's a common occurrence that can happen without periodic maintenance, and typically is caused by a medley of dust, mildew and bacterial slime.

Investigating a DIY fix for your air conditioner leak

You could call a professional to come to help you with a drippy air conditioner. But that could cost a big chunk of change, and during a hot summer it might take a few days before a service person can come to your house to take a look. In the meantime, you'd either must turn off your AC to stop the leak or start using buckets to catch the falling water.

However, this problem is easy to fix and requires no special skills. Read the instructions below to fix your AC water leak yourself.

Step-by-step directions to stop the air conditioner leak

Supplies needed

• Small bottle brush
  
• Wet/dry vacuum cleaner
  
• Spray bottle containing a cup of bleach or vinegar
  
• Paper towels.

Instructions to stop the AC leak 

1. For safety, turn off your AC system before you begin. You'll want to wait a little while to let the leaking water drain.
2. Look for the drain tube from the condensate collection pan outlet. It's usually a PVC pipe located below the coolant line connections.
   
3. Disconnect the drain tube from the collection pan outlet and use the wet/dry vacuum to suck up any remaining water coming out of the drain.
   
4. Carefully insert a small bottle brush to ream out the tube. You want to clear out as much gunk as you can. After that, spray some bleach or vinegar into the outlet hole.
   
5. Next, use the wet/dry vacuum to suck out any debris or other gunk that might have accumulated in the pipe. Afterwards, pour a little bleach or vinegar down the drainpipe to kill any mold or mildew.
   
6. Reattach the drain tube to the collection pan outlet. You should be good to go.
   

What if my drain piping is glued in place?

If you try to remove the plastic drain piping from the pan outlet but find that it's glued in place, you still have a path forward to resolve your leak. You'll need to saw off some of the PVC pipe and then make a new detachable connection.

Additional supplies needed

• A saw to cut the PVC pipe
• Gas pliers
• PVC coupling

Instructions

1. Look for a straight section one or two inches downstream from where the PVC pipe connects to the thread pan outlet connection and cut the pipe.
2. Using a pair of gas pliers, unscrew the PVC pipe from the threaded pan connection.
   
3. Clean out the pan and drain piping as described above.
   
4. Reattach the threaded PVC connections. Use the PVC coupling to join the pipe where you cut it. Don't glue this connection so you can disconnect it for periodic maintenance.
   
5. Because periodically cleaning the condensate drain and pipe is cheaper than cleaning up a costly leak, it pays to make the job easier by installing a simple clean-out using a T-joint and a snugly fitting pipe cap. Just make sure you don't install the T-joint downstream from the condensate trap. Just like a sink trap, condensate traps fill with water. This protects your AC system's efficiency by preventing cooled air from blowing away down the drainpipe.

What if your window unit is leaking?

Window air conditioners can be another source of water infiltration, especially if they aren't installed properly. If you see water coming into the house from your window unit, the 1st thing to do is check the angle of its posture in the window. The appliance should be angled slightly downward on the outside of the window, so that the water will accumulate at the back of the drain pan and drip safely outside the house.

If the air conditioner is installed at the proper angle but you're still having a water problem, make sure that the filter and coils are clean. If the unit is not kept in good condition the condensation can accumulate and migrate to inconvenient places – like the inside of your house. Finally, check the condensation pan itself and its drain to make sure there's no clog or debris blocking the water from getting out.