When your central air conditioner or heat pump cools your house, condensation forms on the cold evaporator coil as moist household air passes across it. To protect your furnace and home from the water damage that air conditioner condensation can cause, a condensate tray, a drain line and sometimes a drip pan collect and dispose of the condensation.
How Condensate Draining Works
The condensate tray sits below your air conditioner’s evaporator coil to collect the condensation that drips from the coil. The coil and tray are usually in your attic or the main duct above the furnace.
Usually, gravity drains water from the pan through a drain line to a drain, sink, or outdoors. If the water can’t flow by gravity, a condensate pump moves it. Local building codes might specify where the pump can discharge the water and usually prohibit discharging onto your roof or into a plumbing vent or stack.
Some homes have a drip pan under the pan to catch the water that might overflow from the condensate tray located in an attic. The drip pan should have its drain line. An alternative is a float switch in the condensate tray that shuts off the air-conditioner when the water level in the pan is too high.
Common AC Condensation Problems
The condensate tray must work properly, or the excess water drips onto the heat exchanger (the most critical component of the furnace) and can rust it prematurely, necessitating that you replace the furnace.
Although you can’t see the condensate tray, you sometimes see signs that it’s malfunctioning. Water stains on the top of the furnace indicate that the condensate tray is cracked or tilted. It can also mean that the pan is overflowing because the plug to the drain line is clogged. Or the condensate line could be leaking, missing, broken, or plugged.
Condensate pumps are prone to failure, so if you have one, check it monthly. If your pump does break, it’s relatively inexpensive and easy to replace. Also, check drain lines, if you can access them, to make sure they’re attached to their pan, are flowing freely and have no leaks.
If your central air unit requires maintenance or repair, it’s best to hire a qualified HVAC contractor.