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The Dreaded A/C Water Leak

by admin on June 21, 2012

The float switch (looks like an upside down "T") will shut the a/c down if the primary drain line clogs.

The single most frustrating summer repair call for an A/C contractor has got to be the water leak.  A water leak from the a/c system can be difficult to prevent and hard to diagnose.  Additionally, it can cause significant property damage.

Where does the water come from?

The water from an A/C system actually comes from the air in your home.  As you A/C unit runs, it dehumidifies the air.  The dehumidification process basically means that moisture is being taken out of the air and turned into water.  If everything is working as it’s supposed to, this water then gets drained to the outside.

How does the A/C system make the water?

All air conditioning systems have an evaporator coil, more commonly called an A Coil.  This is basically a part made up of metal tubes that get very cold when the A/C unit is turned on.  As these tubes get cold and air is blown across them, moisture begins to condense just as it would on the outside of a cold can of soda.  Eventually enough moisture forms that it drains off into a pan underneath the A Coil.  This pan has a plastic drain coming off of it that takes the water outside your home.

So what causes the water leaks?

There are several things that can go wrong and cause the water to overflow into your home.  We’ll cover the 2 most common.

#1  Clogged Drain Line – The most common of these is the clogged drain line.  Over time, as water flows thru the drain, a substance that experts refer to as gunk (ok, I call it gunk – I’m not sure what the experts call it) begins to accumulate.  Eventually enough gunk builds up that it can completely clog the drain line.  If the drain is clogged the water has no place to go except over the side of the drain pan and into your house.

#2  Rusted or Cracked Drain Pan – Another slightly less common cause of water overflow is the rusted out or cracked drain pan.  The drain pans that initially catch the water are typically made of metal or plastic.  As you know, metal rusts and plastic gets brittle, especially when it is in a 140° attic for extended periods of time.  When a hole develops in the bottom of the pan, the water is going to go through that hole instead of down the drain like it’s supposed to.

What can you do to prevent an a/c water leak?

#1  Have annual maintenance performed on your cooling system, and make sure that the service provider flushes the drain line as a part of this maintenance.

#2  Invest in an overflow shut off device that is installed on the drain line.  These little gadgets will turn off your air conditioner if the drain line backs up.  Most of the time these will completely prevent any water from overflowing the pan.

#3  Invest in an audible alarm that can be placed underneath your A-Coil.  These are inexpensive, battery powered devices that will start to scream at you if they get wet – kinda like a cat, but you don’t have to buy food or kitty litter.

#4  I hesitate to put this one in here, but some people do this and have no problems with it.  If you’re a/c drain extends all the way outside, you can pour a cup of bleach down the drain every couple of months to prevent the buildup of gunk.  Be careful though.  We’ve seen cases where the drain didn’t extend all the way outside, but instead dumped the bleach onto the copper freon lines. The bleach can eat through the copper lines, resulting in even more problems.

When it comes to water leaks, the old saying “an ounce of prevention is worth a pound of cure” certainly applies.  Take a little time to locate you’re a/c drain inside your home, as well as where it terminates outside the house (usually close to the outdoor a/c unit).  See if you can identify the overflow shut off device mentioned in #2 above.  It will have a wire coming off of it and going inside your blower.  If you’re not sure what you’ve got, take a couple of pictures of your drain setup and email them to us at .  We’ll do our best to answer any questions you have.