What causes my central air conditioning system to leak water?

One of the functions of your central air conditioning system is to remove the humidity from your home. Actually, it is the primary function of your air conditioning system – the cooling of your home is the benefit of its operation. 

When your air conditioning system runs, warm air flows across the cold evaporator coil. As the coil absorbs the heat from the air, it collects moisture – much like a glass of cold water on a hot day. This moisture then drips down into a condensate pan, and runs into a condensate line to the outside of your home or to a local drain. The more warm and humid it is inside your home, the more the condensation builds, and the more forceful the water is sent through the drain system.

When your air conditioning system is routinely serviced and is working well, there is no issue with this process. However, if your system is neglected, the result can be catastrophic and can lead to serious problems.

If you notice water around your air conditioning system, mold or mildew growing around the vicinity of the indoor equipment, experience increased humidity in your home or see a water bubble form in your ceiling – SHUT YOUR AIR CONDITIONING OFF - to prevent further damage to your home. These are the signs that your system is in need of service.

Common causes of condensate leaks are:

Clogged drain line – a clogged drain pipe can cause the water to back up in the condensate pan. This is the most common type of water leak and is typically caused by the build up of dirt, rust, algae or other debris that gathers inside the condensate line. The back up of water can also cause water to leak into the electrical system of your indoor unit and short out control boards and wires.

Disconnected drain line – if the condensate piping was not secured and properly assembled when it was installed, or not properly reconnected at the time of your last service, it can loosen and disconnect, causing water to flow all around your home. If your indoor unit is located in your attic, it can be catastrophic, as the water will eventually cause your ceiling to come down, and any lighting fixtures can be damaged.

Cracked condensate drain line – when work is provided near the condensate line of your air conditioning system, it is important that you are careful to stay away from the piping. Typically these pipes are white plastic PVC, but can be black and hard to detect. Putting undue pressure or stepping on the piping can cause it to crack, allowing water to flow freely onto your floor or ceiling.  When outside contractors work around your indoor air conditioning unit, please point out the piping and let them know to be careful.

Condensate pump failure – a malfunctioning or dirty condensate pump can also cause water leakage from your air conditioning system, flooding your attic or basement. Like drain lines, dirt, rust, algae or other debris can cause your condensate pump to stop working. A condensate pump can also stop working because it is no longer operationally sound, which would require complete replacement.

Damaged drain pan – in every indoor unit, there is a drain pan that is situated under your evaporator coil. Its purpose is to collect the water that drips from the coil. When this pan is rusted or cracked, it causes the water to drip into the unit, bypassing the condensate drain line system. In many cases, manufacturers maintain parts for the indoor equipment. If your equipment is older, it may create the need to replace your equipment as parts become phased out.

Low refrigerant – when your system loses small amounts of refrigerant, it results in freezing of the refrigerant lines and the evaporator coil, sometimes causing a block of ice to form inside the indoor unit.  This not only causes water to leak all over the inside of your unit, it blocks air flow in your system, which can be noticed by reduced air flow. With older air conditioning systems, it is important you identify the source of the refrigerant leak, as environmental regulations restrict the adding of older refrigerant types to your equipment.

Blocked air filter – lack of maintenance to your air conditioning system, and the lack of frequent replacement of air filters causes dirt and small particles to enter the air stream into your equipment. These substances latch onto your indoor evaporator coil, and when the coil condensates the dirt laden water is sent into your condensate drain lines, causing clogs in the piping – see "clogged drain line" above.

To avoid damage from water leakage, follow these tips:

  • Clean or change your air filter every month during summer operation

  • Have a professional check your system annually to ensure proper refrigerant levels and to clear your condensate line(s). Also ask them to check if your condensate lines are properly installed.

  • Keep your condensate pump free from mold and mildew by flushing it with a 50% bleach/water solution.

  • If you air handler is located in the attic, make sure you have a safety pan under your unit to catch drain pan overflow – this provides a secondary drain source should your primary drain overflow.

  • For added protection, install a drain pan overflow shutoff switch to automatically shut down your air conditioning system when your condensate system fails.

If you suspect there is something wrong with your air conditioning system, consult with a professional. Knowledgeable technicians can provide you with the proper assessment of your system and provide options to repair your equipment.

As with all home improvements or home repair services, make sure you select a company that is licensed and insured to do work in New York City, and who is capable of providing the services you need. Ask for references and check their reviews online to ensure their customers are satisfied with the services they were provided.

Vincent Laurino, General Manager
Bob Mims Heating & Air Conditioning
(718) 273-8175
www.bobmims.com     

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