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  • Writer's pictureVirginia Air

Question for August: Why is my air conditioning unit leaking water?

A frequent question we at Virginia Air Heating and Cooling encounter during the summer months has to do with an air conditioning indoor unit leaking water. There are a several reasons why an air conditioning unit could be leaking water which we want to highlight in our monthly blog.

AC Indoor Leaking Water #1 Reason: Dirty Air Filters

Dirty Air Filters will block your air flow. When the air can’t go through the filter, it starts to freeze. If your air conditioning air filter becomes clogged or even partially blocked, it can cause the unit’s evaporator coils to freeze, which causes extra water to overflow from the drainage pan. Once you experience an indoor water leak caused by your HVAC system, the next two following causes below can become a more frequent issue due to the water rusting the system.

AC Indoor Leaking Water Reason: Low/Leaking Refrigerant

A loss of refrigerant could cause your AC to freeze up then leak water. When a unit is low on refrigerant, it starts to freeze up when the compressor is running. If the refrigerant level in your AC is too low, it causes the unit to lose pressure. This can cause coils to freeze like a block of ice on and around the indoor coil which may miss or overflow the drain pan as it melts and/or the unit to sweat leaking water on the outside of the unit as well as the inside of the unit.

AC Indoor Leaking Water Reason: Drain Line Back Up

If your drain line backs up and the drain pan is overflows, this will cause your ac unit to leak water. When a drain line gets clogged with debris, water flow is impeded and has nowhere else to go except back up into the pan. The condensate pan is a small tray designed to catch the water in the direction the water falls from the indoor coil. Once the pan fills with water, it will overflow and leak.

AC Leaking Reason: Duck Work Installation

Both in the heating and the cooling season, condensation can form either on the outside or the inside of ducts that are poorly insulated. This is the most common cause of water leaking from the HVAC vents.


Many people don’t realize that 80% of the time, this issue could have been avoided through performing preventive maintenance on the air conditioning unit which is just one of the many reasons why we always encourage membership in our Home Comfort Club.


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