does an ac contactor receive just a 24vdc pulse



Have you ever wondered how an AC contactor works? One common question is whether an AC contactor receives just a 24VDC pulse. In this article, we will delve into the intricacies of AC contactors and shed light on this intriguing query. AC contactors play a vital role in controlling the flow of electricity in air conditioning systems, and understanding their operation is key to ensuring efficient and safe functioning. So, without further ado, let's dive into the functioning of AC contactors and explore whether they solely rely on a 24VDC pulse.

The Basics of an AC Contactor

An AC contactor is an essential component of HVAC systems, responsible for controlling the electrical current to various parts of an air conditioner, such as the compressor, condenser fan motor, and blower motor. Contactors are electromechanical devices consisting of a coil and contacts, and they serve as switches for the flow of electrical current.

When the coil of an AC contactor is energized, it creates a magnetic field that attracts the contacts, closing the circuit and allowing the current to flow through. This circuit closing enables the different components of an air conditioning system to operate, such as the cooling process or air circulation.

Understanding the Operation of an AC Contactor

The operation of an AC contactor involves more than receiving a 24VDC pulse. Let's explore the various stages of an AC contactor's functioning to gain a comprehensive understanding.

1. The Control Circuit

The control circuit is responsible for activating the coil within the AC contactor. Typically, the control circuit comprises a transformer, low voltage control wiring, a thermostat, and a contactor relay. When the thermostat detects that cooling or heating is required, it sends a signal to the contactor relay, energizing the coil and initiating the operation of the AC contactor.

The 24VDC pulse you mentioned is supplied by the transformer in the control circuit. The primary side of the transformer is connected to the main power supply, while the secondary side outputs a lower voltage, usually 24 volts. This lower voltage is then sent through the control wiring to activate the coil within the AC contactor.

2. Contact Closure

Upon receiving the 24VDC pulse, the coil of the AC contactor becomes energized, generating a magnetic field. This magnetic field attracts the contacts, causing them to close. The closing of the contacts establishes an electrical connection between the line and the load side of the contactor.

When the contacts close, the electrical current flows through the contactor's moving contacts, allowing the current to reach the various components of the air conditioning system. This energizes the compressor, fan motors, and other essential elements, enabling the AC unit to provide the desired cooling or heating.

3. Continuous Current Flow

Once the AC contactor's contacts are closed, they maintain the connection until the control circuit signals them to open again. This continuous current flow ensures the uninterrupted operation of the air conditioning system, with the contactor serving as a reliable switch for managing the flow of electrical power.

It is crucial to note that the contactor does not constantly receive the 24VDC pulse; instead, it only required during the operation's initiation and termination stages. During normal functioning, the contactor's contacts remain closed, allowing the current to flow continuously, without relying on the 24VDC pulse.

4. Contactor Coil Deactivation

When the desired temperature is achieved, and the thermostat signals the system to stop cooling or heating, the control circuit sends a signal to deactivate the coil within the AC contactor. This deactivation interrupts the generation of the magnetic field, causing the contacts to open. As a result, the electrical connection to the various components of the air conditioning system is disrupted, ceasing their operation.

5. Contact Arc Suppression

When opening or closing the contacts of an AC contactor, a small arc is produced due to the electrical current passing through. This arc, if left uncontrolled, can cause damage to the contacts over time. Hence, contactors are equipped with arc suppression mechanisms to prolong their lifespan and ensure reliable operation.

Arc suppression can take various forms, such as using snubber circuits, resistance capacitors, or the incorporation of magnetic blowouts. These mechanisms help reduce the arcing that occurs when the contacts make or break the electrical connection, thereby safeguarding the contactor and promoting its longevity.


In summary, while a 24VDC pulse is indeed used to activate the coil within an AC contactor, it is not the sole source of power for its operation. AC contactors serve as switches that control the flow of electrical current in air conditioning systems. Once energized, the contacts close to provide continuous current flow to various components of the AC unit, allowing it to function efficiently.

Understanding the operation of AC contactors is essential for HVAC technicians and enthusiasts alike. By familiarizing ourselves with their functioning, we can appreciate the critical role they play in maintaining the comfort and temperature control in our homes and buildings. So, the next time you think about AC contactors, remember that their operation involves more than just receiving a 24VDC pulse.


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