How to wire a condensate pump to ac

Updated February 21, 2017

An AC condensate pump pushes condensate water from an air conditioning unit's inside coil through a 3/8-inch copper water line to the exterior. Used when gravity fed drain lines will not work, condensate pumps employ high voltage to run the pump motor and a low voltage emergency shut-off switch. The shut-off switch off power to the air conditioner if the pump fails, preventing a condensate water flood. Inside of the condensate pump a floating switch turns on and off the pump motor when the condensate water level reaches predetermined levels inside the pump housing.

Flip the circuit breaker labelled "air handler" or "furnace" to the "Off" position. Turning the AC thermostat to the "On" position will verify that the unit does not have power, if the unit does not turn on.

Open the top panel of the air conditioning unit's furnace with a nut driver, usually 1/4- or 5/16-inch. Place the screws in a safe place for reinstallation.

Open the wire-clamp through which the thermosat wires enter the furnace with a flat screwdriver. A wire-clamp has two screws that hold a bracket in place. The wires slide between the bracket and the clamp's housing. The thermostat wire has a brown plastic sheathing that covers several thin colour-coded wires.

Push the high voltage wire from the condensate pump through the wire-clamp and into the furnace. The condensate pump has two sets of wires, a thick set of high-voltage wires and a thin set of low-voltage wires. Each set of wires have two separate strands of insulated wire in them.

Check the condensate pump tag, found on the pump's housing, to verify whether the pump runs with 110- or 220-volts.

Connect the high voltage wires from the condensate pump to the furnace. If the pump connects to a 220V power source then use the flat screwdriver to open both wire lugs on the furnace's terminal block. Connect a high-voltage wire strand to each side of the terminal block and retighten the wire lugs. If the condensate pump uses a 110V power source then connect one high-voltage wire strand, from the condensate pump, to one side of the terminal block and one strand to the ground block. The furnace's terminal block has thick wires from the circuit breaker connected to it and the grounded block has bare copper wires connected to it.

Push the low-voltage wire from the condensate pump through the furnace's wire clamp.

Find the low-voltage red wire coming from the thermostat wire to the transformer. The transformer has a block shape with several wires entering it. Two of these wires go to the terminal block and one wire connects to the low-voltage thermostat wire and one wire connects to the ground block.

Remove the wire nut connecting the red wire to the transformer.

Connect the red wire to one of the low-voltage strands of wire coming from the condensate pump with a wire nut.

Connect the other low-voltage wire from the condensate pump to the loose wire from the transformer with a wire nut.

Screw the furnace access panel back onto the furnace with the saved screws. Tighten the wire clamp screws. Flip the furnace circuit breaker on.

Fill the condensate pump with water to test the pump.

Things You'll Need

  • 1/4- or 5/16-inch nut driver
  • Flat screwdriver
  • Wire nuts
  • Water
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About the Author

Based out of Central Florida, Robert Sylvus has been writing how-to and outdoor sports articles for various online publications since 2008. Sylvus has been a home improvement contractor since 1992. He is a certified HVAC universal technician.