how to hook up ac contactor


How to Hook Up AC Contactor


Are you looking to hook up an AC contactor but not sure where to start? Look no further, as we have all the information you need to successfully connect your AC contactor! Whether you are a beginner or have previous experience with electrical installations, this step-by-step guide will walk you through the process. An AC contactor plays a crucial role in controlling the flow of electricity to your air conditioning unit, making it essential to install it correctly. So, let's dive in and learn how to hook up an AC contactor!

The Basics of AC Contactors

AC contactors are electrical devices commonly used in heating, ventilation, and air conditioning (HVAC) systems. They act as a switch that controls the electrical current flowing to the compressor, blower motor, and other components of an HVAC unit. AC contactors consist of a coil and contacts. The coil generates a magnetic field when an electrical current passes through it, which allows the contacts to close or open, depending on the circuit requirements.

When the coil is energized, the contacts close, allowing electricity to flow through the circuit. On the other hand, when the coil is de-energized, the contacts open, interrupting the electrical current. This process ensures efficient operation and control of the HVAC system. Now, let's move on to the installation process of an AC contactor.

Gathering the Required Tools and Equipment

Before you begin installing the AC contactor, it is essential to gather all the necessary tools and equipment. Having everything prepared beforehand will help streamline the installation process. Here are the tools and equipment you will need:

1. Screwdriver set: You will require both flathead and Phillips screwdrivers for various screws during the installation.

2. Wire strippers: These specialized tools will help you strip the insulation off the wires for a proper connection.

3. Electrical tape: Use electrical tape to secure and insulate the wires, preventing any potential short circuits.

4. Wire nuts: Wire nuts are connectors used to secure and join wires together. They ensure a reliable and safe electrical connection.

5. Multimeter: A multimeter is a versatile tool that allows you to measure voltage, resistance, and continuity. It is useful for testing the electrical connections and troubleshooting any issues.

6. AC contactor: The main component of this installation process. Ensure you have the correct contactor as per the requirements of your specific HVAC system.

With these tools and equipment ready, let's move on to the installation process.

Shutting Off the Power

Safety should always be the top priority when working with electrical components. Before initiating any installation or wiring process, make sure to shut off the power. Turning off the power supply will prevent any electrical shocks or accidents during the installation. Locate the electrical breaker that controls the HVAC system and switch it off. Additionally, use a voltage tester to ensure that the power is effectively cut off before proceeding to the next steps.

Locating the AC Contactor

To begin the installation process, locate the existing AC contactor in your HVAC system. The AC contactor is typically found near the condenser unit, which is the outdoor part of your air conditioning system. It is housed inside a metal box known as the contactor enclosure. If you cannot locate the contactor or are installing a new one, consult the HVAC system's manual or contact a professional for guidance.

Removing the Old AC Contactor

If you are replacing an existing AC contactor, the next step is to remove the old one. Start by disconnecting the electrical supply wires that are connected to the contactor. These wires transmit the electrical current to the contactor's coil. Use a screwdriver to unscrew the wire terminals and gently pull the wires away from the contactor.

After disconnecting the electrical supply wires, you need to remove the low-voltage control wires. These wires may be connected to a separate terminal board or directly to the contactor. Carefully unscrew the nuts or terminal screws to release the low-voltage wires.

Once all the wires are disconnected, take note of the location and orientation of the old AC contactor. This will help you correctly install the new contactor. With the old contactor removed, it's time to proceed to the next step.

Installing the New AC Contactor

Now that the old AC contactor has been removed, it's time to install the new one. Begin by aligning the new contactor in the same position and orientation as the previous one. This will ensure that the electrical connections match up correctly.

Start by connecting the low-voltage control wires to the new contactor. Loosen the terminal screws and insert the wires into their respective positions. Tighten the screws to secure the wires in place. Ensure that the low-voltage connections are properly insulated and that no exposed wires are visible.

Moving on to the electrical supply wires, connect them to the appropriate terminals on the new contactor. Typically, there are separate terminals for the line (high voltage) and load (to the compressor and other components). Use a screwdriver to fasten the wire terminals securely. Take care to connect each wire to the correct terminal as misconnections can lead to system malfunctions or damage.

Testing the AC Contactor

After successfully installing the new AC contactor, it's important to verify its functionality. Testing the contactor will ensure that it operates correctly, allowing for the smooth functioning of your HVAC system. Here's how you can test your newly installed AC contactor:

1. Double-check all the electrical connections and ensure they are secure.

2. Switch on the power supply to the HVAC system.

3. Set your thermostat to the desired cooling temperature.

4. Observe the contactor and listen for a clicking sound when the thermostat signals for cooling.

5. The contactor's coil should energize, closing the contacts, and allowing the electrical current to flow smoothly.

6. If the contactor does not activate or there is a buzzing sound, turn off the power supply immediately and recheck the wiring connections.

7. If the contactor works as expected, you have successfully hooked up your AC contactor!


In summary, hooking up an AC contactor is a crucial step in maintaining an efficient HVAC system. By following the step-by-step installation guide provided above, you can confidently connect your AC contactor while ensuring safety and reliability. Remember to gather the required tools, shut off the power supply, locate and remove the old contactor, install the new contactor correctly, and test its functionality. If you encounter any difficulties or are unsure about any step, it is advisable to seek the assistance of a qualified electrician or HVAC professional.


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