What Is An HVAC Condensate Pump, Why Does Your AC Need It, And What Pump Malfunctions Can Thwart Your System?

The air handler portion of your central air conditioner is inside your home, normally in the furnace, and contains the parts that make up the final stages of the cooling cycle. The parts include the evaporator coils, which receive a liquid refrigerant from the outside condensing unit and perform a phase change that both makes the refrigerant a gas and makes the surface of the coils cold. The cold coils chill the circulating ambient air that is then passed back into your home.

The evaporator coils have some correlated parts important to making the system work effectively and safely. One of those parts is the condensate pump, which is located in the drain tray at the bottom of some air conditioners.

Condensate Pump Function

The evaporator coils become moist during the phase change that ultimately cools the coils. That moisture forms condensate, which needs a place to go since a lot of dripping water doesn't mesh well with machinery. The air handler has a drip pan at the bottom that catches the condensate. The drip pan is connected to a drainpipe. How does the condensate get from the pan to the drainpipe?

There are two different ways that the water gets to the pipe, depending on the type of system you have. If your air conditioner is on a basement floor that has a bit of a gradient, gravity alone will get the water out of the pan. But some units aren't tilted at the right angle for gravity to work or work enough to empty the pan. That's where a motorized condensate pump comes in. The pump pushes the water into the drainpipe and out of the condensate pan. 

Potential Malfunction: Broken Pump Won't Drain Pan

Condensate pumps, like any motorized part, can start to fail or outright break. A failing pump won't push out enough of the drain pan water fast enough. A broken pump won't push out any water at all. Both scenarios can lead to the drain pan overflowing onto the floor of your air handler and basement, which can cause expensive water damage over time.

Potential Malfunction: Clogged Drainpipe Counteracts Pump

The drain pan can overflow even though the condensate pump is working properly or close to properly. The drainpipe itself can clog and the clog will push the water back up, which counteracts the function of the condensate pump.

You should be able to tell whether the problem is the pump or the pipe by opening the air handler, looking at the drain pan, and examining how the water is leaving. If the surface water is moving in a rhythmic pumping fashion but doesn't seem to really go anywhere, the pipe is likely clogged. If the water is draining out slowly but the surface isn't moving much, then the condensate pump is likely failing.

If you are unsure about the nature of the problem, call in HVAC contractors to help.