what does a contactor do on an ac unit


What Does a Contactor Do on an AC Unit?

Have you ever wondered what happens behind the scenes when you turn on your air conditioning unit? There are numerous components working together harmoniously to ensure your comfort, and one such crucial element is the contactor. While it may seem like a small part of the overall system, the contactor plays a vital role in the operation of your AC unit. In this article, we will delve into the functions and importance of a contactor and understand why it is an integral part of your air conditioning system.

The Basics: Understanding the Contactor

A contactor is an electrical switch that controls the flow of electricity within an AC unit. It consists of a coil, contacts, and a spring-loaded button. When you lower the temperature on your thermostat or turn on your air conditioning system, a signal is sent to the contactor, prompting it to engage and allow electricity to flow through the unit. Essentially, a contactor acts as the intermediary between the thermostat and the compressor, condenser, and fan motors.

The Role of the Contactor

Now that we have a basic understanding of what a contactor is, let's dive deeper into its role in an AC unit:

Ensuring Proper Voltage: One of the primary functions of a contactor is to facilitate the transfer of voltage from the main power source to the various components of the air conditioning system. It allows for seamless electrical flow, avoiding any disruptions that could lead to equipment failures or malfunctions.

For instance, when you turn on your air conditioning unit, the contactor receives a low-voltage signal from the thermostat. This signal energizes the coil within the contactor, causing the main contacts to close and connect the high-voltage power supply to the compressor and fan motors. Without a contactor, the high-voltage electricity would directly flow to the motors, overwhelming them and potentially causing severe damage.

Engaging and Disengaging the System: Another essential role of a contactor is to engage and disengage the air conditioning system as instructed by the thermostat. When the desired temperature is reached or when the thermostat is turned off, the contactor receives a signal to open the main contacts, effectively cutting off the power supply to the compressor and fan motors.

This action prevents the system from continuously running, saving energy and ensuring that the compressor and fan motors do not wear out prematurely. Proper engagement and disengagement of the system contribute to its longevity and efficient operation.

Protecting Against Power Surges: Electrical power surges can occur due to various reasons, such as lightning strikes or fluctuations in the main power grid. These surges can be damaging to electrical appliances, including your air conditioning unit. To safeguard the system against power surges, contactors are often equipped with surge protection features.

These protective components help mitigate the impact of power surges by absorbing excess voltage and preventing it from reaching sensitive parts of the AC unit. By doing so, the contactor acts as a defense mechanism, preserving the integrity of the system and preventing costly damages.

Managing Motor Loads: Air conditioning systems rely on motors to operate the compressor and fan blades. However, these motors require a significant amount of electrical current to function optimally. The contactor plays a crucial role in managing the electrical load on these motors.

When the contactor engages, it closes the main contacts, allowing electricity to flow to the motors. It ensures that the motors receive the necessary current and voltage to perform their tasks efficiently. Furthermore, contactors are often rated for specific motor loads, ensuring compatibility and preventing overload situations that could lead to motor burnouts.

Preventing Voltage Drop: Voltage drop is a phenomenon that occurs when electrical current encounters resistance within a circuit. When voltage drop happens, the voltage reaching the components decreases, affecting their performance. Contactors, with their low electrical resistance, minimize voltage drop within an AC unit.

By providing a stable and controlled pathway for the electrical current, contactors reduce the chances of voltage drop occurring. This, in turn, ensures that the AC unit operates optimally, delivering the desired cooling or heating output without any compromise in performance.


The contactor may be a small component in your air conditioning unit, but its importance cannot be overstated. From facilitating the transfer of electricity to protecting against power surges and managing motor loads, the contactor plays a vital role in the efficient operation of your AC system.

Next time you turn on your air conditioner, take a moment to appreciate the intricate workings of this essential device. Without the contactor, the smooth operation of your AC unit would be compromised, leading to uncomfortable living conditions and potential damage to the system. So, while it may remain hidden from plain sight, the contactor is undoubtedly an unsung hero in the world of air conditioning.


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