how to hook up contactor on ac unit



Contactor is an indispensable component in an AC unit, responsible for controlling the flow of electrical current to the unit's compressor and condenser fan motor. It acts as a switch that turns the unit on and off based on the temperature settings. Properly hooking up the contactor on your AC unit is essential to ensure efficient cooling and avoid potential electrical hazards. In this article, we will guide you through the steps involved in hooking up a contactor on an AC unit.

Understanding the Contactor:

The contactor is a crucial part of the electrical circuitry in an AC unit. It is an electromagnetically-operated switch that allows or interrupts the electrical current flow. A typical contactor consists of several terminals where wires are connected, and it is controlled by a low voltage signal from the thermostat. When the thermostat calls for cooling, it sends a signal to the contactor, which energizes the unit's compressor and condenser fan motor. Understanding the different terminals and their functions is crucial when hooking up a contactor.

Locating the Contactor:

Before proceeding with the hookup process, it is essential to locate the contactor in your AC unit. Typically, the contactor can be found near the condenser unit, which is the outdoor part of the AC system. It is housed inside a metal or plastic enclosure and has wires connected to it. Once you have located the contactor, ensure that the power to the unit is turned off to prevent any electrical shocks.

Wiring the Contactor Step-by-Step:

Here, we will guide you through the step-by-step process of wiring the contactor on your AC unit. Proper wiring is critical to ensure the safe and efficient operation of the unit.

Step 1: Prepare for Wiring:

Before starting the wiring process, gather all the necessary tools and materials required for the job. These may include a screwdriver, wire strippers, electrical tape, and the appropriate gauge wires for the job. It is also crucial to refer to the AC unit's wiring diagram or consult the manufacturer's instructions to ensure you are following the correct wiring configuration.

Step 2: Identify the Power Supply:

Identify the power supply wires coming into the contactor. These wires are typically thick gauge and carry high voltage. There are two power supply wires - the line wire (commonly black) and the load wire (commonly red). The line wire carries the power from the electrical panel to the contactor, while the load wire carries the power from the contactor to the compressor and condenser fan motor.

Step 3: Connect the Power Supply Wires:

Strip the ends of the power supply wires to expose the bare copper. Place the line wire under the line terminal and the load wire under the load terminal of the contactor. Tighten the terminal screws securely to ensure a solid electrical connection. It is essential to double-check the wire connections to avoid any loose or faulty connections.

Step 4: Connect the Control Wires:

The control wires are responsible for signaling the contactor to turn on or off. These wires come from the thermostat and carry a low voltage signal. There are two control wires - typically one is red and the other is white. The red wire carries the power signal, and the white wire is the common wire. Connect the red control wire to the power terminal of the contactor, and the white control wire to the common terminal. Again, tighten the terminal screws securely to establish a secure connection.

Step 5: Secure the Wires:

After connecting all the wires to their respective terminals, it is crucial to secure them properly. Use cable ties or electrical tape to bundle the wires neatly and prevent any potential damage from vibration or movement. Ensure that the wires are not pinched or stretched excessively, as this can lead to short circuits or loose connections.


Hooking up a contactor on an AC unit may seem complex, but by following the step-by-step process and understanding the different terminals, it can be accomplished safely and effectively. Proper wiring is crucial for the reliable and efficient operation of the AC unit. Remember to consult the AC unit's wiring diagram or manufacturer's instructions and take necessary safety precautions throughout the process. By ensuring a secure and accurate hookup, you can enjoy the comfort of a well-functioning AC unit.


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