how contactor work in ac


How Contactors Work in AC


When it comes to understanding how air conditioning systems function, it's essential to have a clear understanding of the different components involved. One such crucial element is the contactor, which plays a vital role in the operation of an AC unit. In this article, we will delve into the working mechanism of contactors in ACs, exploring their purpose, components, and functionality. So, let's dive right in and gain a comprehensive understanding of how contactors work in AC systems.

The Purpose of Contactors in AC Systems

A contactor for an AC unit is an electrical device that serves as a switch for controlling the flow of electrical power to various components of an air conditioning system. Its primary purpose is to allow or interrupt the electrical current flowing to the compressor, condenser fan motor, and other high-power consuming devices. Contactors are typically found in both residential and commercial air conditioning systems and are designed to handle heavy electrical loads.

Components of a Contactor

A contactor comprises several key components that work in harmony to ensure the proper functioning of an AC system. Let's take a closer look at these components:

1. Contact Points

The contact points, also known as contacts or terminals, are the heart of a contactor. They consist of stationary and moving parts that come into contact with each other. These points are made of highly conductive materials like copper alloy with silver or silver-nickel tips for efficient energy transfer. When the electromagnet within the contactor is triggered, the contact points close or open, allowing or interrupting the flow of electrical current.

The stationary contacts are typically attached to the mainframe of the contactor, while the moving contacts are fastened to a movable arm or plunger. When the contactor is energized, the electromagnetic pull attracts the plunger, causing the stationary and moving contacts to come into contact, establishing an electrical connection. Conversely, when the contactor is de-energized, the electromagnetic field subsides, and the spring-loaded mechanism separates the contact points, breaking the electrical circuit.

2. Electromagnet

An electromagnet is the driving force behind the operation of a contactor. It consists of a coil of wire wound around an iron core. When an electrical current passes through the coil, it generates a magnetic field around the iron core. This magnetic field creates the attractive pull needed to close the contact points and complete the electrical circuit.

The strength of the magnetic field generated by the electromagnet determines the force at which the contact points close. Larger contactors used in industrial air conditioning systems often require stronger electromagnets to handle the higher electrical loads.

3. Coil

The coil is an essential part of the contactor, responsible for energizing the electromagnet. It typically operates on a low voltage, typically 24 volts AC, obtained from the control circuit of the air conditioning system. When the coil receives an electrical signal, it creates an electromagnetic field by inducing a current flow. This, in turn, attracts the movable arm or plunger and closes the contact points.

4. Enclosure

The enclosure houses the various components of a contactor, providing insulation and protection against environmental factors such as moisture, dust, and debris. This protective covering also ensures the safety of individuals by preventing accidental contact with live electrical parts. The enclosures are typically made of materials such as plastic or metal, with some being transparent to allow for visual inspection of the contactor's status.

5. Auxiliary Contacts

Many contactors feature additional sets of contacts known as auxiliary contacts. These secondary contacts operate separately from the main contacts and serve various purposes, such as controlling other electrical components in the system. For example, auxiliary contacts can be used to trigger an alarm or activate a backup power source in case of a contactor failure. These contacts are often designed to open or close depending on the contactor's position, providing additional control and safety functionalities to the air conditioning system.

The Functionality of Contactors in AC Systems

Now that we understand the components of a contactor, let's explore how it functions within an air conditioning system. To better comprehend its operation, let's consider a typical scenario of an AC unit turning on:

1. Control Voltage

When a user adjusts the temperature on the thermostat, it sends a control voltage signal to the control module of the air conditioning system. This control voltage is typically a low voltage AC signal, such as 24 volts.

2. Control Module

The control module, also known as the contactor's power source, receives the control voltage signal from the thermostat. It then amplifies and transmits this electrical signal to the coil of the contactor. The control module ensures that only a low voltage reaches the contactor's coil, minimizing the risk of electrical shock.

3. Energizing the Contactor

When the contactor's coil receives the electrical signal from the control module, it generates an electromagnetic field. This electromagnetic field then attracts the movable arm or plunger, resulting in the closing of the contact points. As a result, the electrical circuit to the compressor and other components is established, allowing the AC unit to receive power.

4. Powering the AC Components

With the contact points closed, the electrical power flows through the contactor and continues to various components of the air conditioning system. These components typically include the compressor, condenser fan motor, and other high-power consuming devices. The contactor enables the flow of electricity, powering these components and initiating the cooling process.

5. Disengaging the Contactor

Once the desired temperature is reached or the user turns off the AC unit, the control voltage signal to the contactor's coil stops. As a result, the electromagnetic field weakens, and the spring-loaded mechanism separates the contact points. This action breaks the electrical circuit, cutting off the power supply to the compressor and other components.


In conclusion, contactors play a pivotal role in ensuring the smooth operation of air conditioning systems. Their ability to handle high electrical loads and precisely control the power supply to various components makes them an indispensable component in AC units. By understanding the purpose, components, and functionality of contactors, individuals can gain a deeper knowledge of how their air conditioning systems work and appreciate the importance of this crucial component.


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