what does ac contactor do


What Does an AC Contactor Do?

Air conditioning units are essential appliances that keep our homes and workplaces comfortable throughout the year. Behind the scenes, these systems rely on various components to function efficiently. One such component is the AC contactor. The AC contactor plays a crucial role in the operation of an air conditioning system, ensuring seamless cooling or heating when needed. In this article, we will delve into the workings and significance of an AC contactor and explore its key functions. Whether you are a homeowner curious about your AC unit's inner mechanisms or an HVAC professional aiming to expand your knowledge, this article will provide you with all the necessary insights.

Understanding the AC Contactor

An AC contactor, also known as an air conditioner relay, is an electrical component responsible for controlling and monitoring the flow of electricity to the compressor and the condenser fan motor in an air conditioning system. It acts as a switch, allowing electrical current to pass through to activate these crucial components when the air conditioning system needs to operate. The contactor essentially bridges the gap between the thermostat, which signals the need for cooling or heating, and the components that generate the desired temperature.

The Structure of an AC Contactor

AC contactors typically consist of several key elements that work together to perform their functions effectively. These elements include:

1. Coil

The coil is the primary component of the AC contactor, responsible for generating an electromagnetic field when a current passes through it. A magnetic field is essential for attracting and closing the contacts within the contactor, enabling the flow of electricity to the necessary components. Once the desired temperature is achieved or the unit needs to be turned off, the coil is de-energized, allowing the contactor to open and break the circuit.

2. Contacts

AC contactors feature multiple sets of contacts that come together when the coil is energized. These contacts provide a pathway for electrical current to flow from the power source to the compressor and condenser fan motor. When the AC contactor opens, the contacts separate, interrupting the power flow and turning off the components.

3. Enclosure

The enclosure serves as a protective covering for the AC contactor, shielding it from environmental factors such as moisture, dust, and debris. It also helps to prevent accidental contact with live electrical parts, ensuring safety during maintenance and inspections.

The Main Functions of an AC Contactor

An AC contactor performs several important functions that contribute to the proper functioning of an air conditioning system. Let's explore these functions in more detail.

1. Controlling the Compressor

The compressor is a vital component of an air conditioning system that is responsible for circulating refrigerant and facilitating heat exchange. When the thermostat senses the need for cooling, it sends a signal to the AC contactor, which, in turn, energizes the coil. The energized coil attracts the contacts, allowing electrical current to flow from the power source to the compressor. This activates the compressor, initiating the cooling process. Once the desired temperature is reached or the thermostat signals the need to stop cooling, the AC contactor opens, breaking the circuit and turning off the compressor.

2. Regulating the Condenser Fan Motor

The condenser fan motor helps dissipate heat from the system by drawing in outside air and blowing it across the condenser coils. Similar to the compressor, the AC contactor controls the power supply to the condenser fan motor. When the AC contactor closes, it allows electricity to flow from the power source to the condenser fan motor, activating it and assisting with heat exchange. Once cooling is no longer required, the AC contactor opens, cutting off the power supply and stopping the condenser fan motor.

3. Preventing Simultaneous Operation

To ensure proper functioning, it is crucial that the compressor and the condenser fan motor do not operate simultaneously. If both were to operate simultaneously, it could lead to excessive pressure in the compressor and compromise the overall performance of the system. The AC contactor prevents this by controlling the electrical supply to these components, allowing them to operate one at a time based on the signals received from the thermostat.

4. Enhancing System Safety

AC contactors not only facilitate the operation of the air conditioning system but also contribute to its safety. The contacts within an AC contactor are designed to handle high electrical currents, ensuring reliable performance even under demanding conditions. Additionally, they are engineered to withstand frequent switching, minimizing the risk of failure or electrical arcing. The enclosure of the contactor provides an added layer of protection, reducing the chance of accidents and electrical hazards.

5. Enabling Remote Control

Many modern air conditioning systems are equipped with smart or programmable thermostats that allow remote control. The AC contactor plays a vital role in enabling this functionality. The thermostat, located at a remote location, sends signals to the AC contactor, instructing it to open or close based on the desired temperature. This remote control capability enhances user convenience and energy efficiency, allowing users to regulate their cooling or heating requirements even when they are away from home or in a different room.


An AC contactor is an essential component in an air conditioning system, responsible for controlling the flow of electricity to the compressor and the condenser fan motor. By bridging the gap between the thermostat and these components, the AC contactor ensures seamless operation and temperature regulation. Understanding the functions and structure of an AC contactor can empower homeowners and HVAC professionals to diagnose and address issues effectively, ensuring the optimal performance and longevity of air conditioning systems. Whether you are an end-user or a technician working in the field, a comprehensive understanding of the AC contactor's role is indispensable for maintaining comfort and efficiency in indoor environments.


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