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Troubleshooting A Rooftop AC Leak

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Rooftop-mounted air conditioner units can be quite common in some regions, particularly in areas where wet soil or flooding pose a concern for ground installation or on homes with flat roofs that are designed for rooftop installation. One issue to watch for if you have a rooftop AC is leaks.

Signs of a Rooftop AC Leak

Often the first signs of trouble will begin inside your home. You may notice wet insulation or mold in your attic in the region below the AC unit. If the water leaks through, there may be water stains or peeling and bubbling paint on the ceiling. Mold may also begin to grow on the damp ceiling or there may even be dripping water.

Depending on the cause of the leak, your AC may also show symptoms. There may be standing water in the drain pan beneath the unit, which will usually be discolored and murky. Your unit may also be cooling poorly, or it may be cycling on and off rapidly. If you can see the unit from the ground, you may notice it icing over.

Common Leak Causes

The most likely cause of a leak is an issue in the condensate drain system. This system consists of a pan to catch draining condensation, which is routed into a drain that runs off the roof. The end of the line may be in an exterior storm drain, or it may end harmlessly at the ground. Inside the AC there may also be a condensate pump to help move the water. If any part of this system becomes blocked, either by debris or algae growth in the lines and drains, the condensation will collect and overflow the pan.

The other common cause of this issue is that the AC is freezing up. There are several causes of freezing, but most likely is either a refrigerant leak in the unit or dirt on the evaporator coils. When either of these issues happens, ice builds up on the outside of lines or coils. The ice causes the unit to overheat and shut down, so your home doesn't cool very well.


For issues in the condensate system, generally all that is needed is a full cleaning of the drain, lines, and drain pan. If your unit has a condensate pump, it may need to be serviced or replaced.

For a frozen unit, more in-depth inspection is necessary. A refrigerant leak may require a leak repair and refrigerant recharging. Dirt in the system means that your AC needs to be fully cleaned, inspected, and tuned up.

Contact an HVAC repair service if you suspect any issues with your rooftop unit.