can u install a contactor backwards ac compressor



Installing a contactor backwards in an AC compressor is a topic that has generated some confusion and debate among HVAC technicians. Some argue that it is possible to do so without causing any harm, while others claim that reversing the contactor can lead to serious damage to the compressor. In this article, we will delve into the subject and explore the consequences of installing a contactor backwards in an AC compressor. We will examine the role of the contactor, the impacts of reversing it, and ultimately determine whether or not it is a safe practice.

The Role of the Contactor:

Before diving into the discussion, it is crucial to understand the role of the contactor in an AC compressor. The contactor, often referred to as a relay, is an electrical component responsible for controlling the flow of electricity to the compressor. It serves as a switch that provides power to the compressor motor, allowing it to function properly.

The contactor consists of a coil and contacts. When the thermostat signals the need for cooling, the coil is energized, creating an electromagnetic field that attracts the contacts. The contacts then close, allowing electric current to flow through and activating the compressor. Conversely, when the thermostat signals the desired temperature has been reached, the coil is de-energized, and the contacts open, thus cutting off power to the compressor.

The Impacts of Reversing the Contactor:

Now let's examine the potential consequences of installing a contactor backwards in an AC compressor. It is important to note that reversing the contactor alters the direction of current flow, ultimately affecting the motor rotation. This has several implications:

1. Improper Motor Rotation: Reversing the contactor leads to a change in the direction of the motor rotation. AC compressors are specifically engineered to rotate in a specific direction, usually clockwise or counterclockwise. Reversing the contactor can cause the motor to rotate in the opposite direction, which may result in severe problems.

2. Lubrication Issues: AC compressors require proper lubrication to ensure smooth operation. Reversing the motor rotation caused by a backwards contactor can disrupt the lubrication process, leading to inadequate oil circulation within the compressor. This lack of lubrication can cause excessive friction, overheating, and potential damage to the compressor components.

3. Compressor Overloading: AC compressors are designed to handle specific loads, which are determined based on the desired cooling capacity. Reversing the contactor can cause the compressor to operate outside its intended load range. This can lead to overloading, causing excessive strain on the compressor motor and potentially leading to motor burnout.

4. Electrical Stress: Reversing the contactor can result in the flow of electricity through the compressor in a non-standard manner. This abnormal electrical flow can subject the compressor motor and associated components to increased stress. Over time, this additional stress can lead to premature wear and tear, shortening the lifespan of the compressor.

5. Warranty Voidance: Installing a contactor backwards in an AC compressor can potentially void the manufacturer's warranty. Manufacturers provide warranties with specific terms and conditions, and any unauthorized modifications, including reversing the contactor, may nullify the warranty coverage. This can leave the owner responsible for any repairs or replacements needed.

The Safety of Installing a Contactor Backwards:

Considering the potential impacts highlighted above, it is evident that installing a contactor backwards in an AC compressor is not a safe practice. The risks of compressor damage, motor burnout, and voiding the warranty far outweigh any perceived benefits.

It is essential to follow industry guidelines, manufacturer instructions, and consult with HVAC professionals when it comes to making modifications or repairs to an AC compressor. By adhering to these best practices, you can ensure the safe and efficient operation of your HVAC system.


In conclusion, installing a contactor backwards in an AC compressor can have detrimental effects on the motor, lubrication, compressor, and overall system performance. The improper motor rotation, lubrication issues, increased electrical stress, potential warranty voidance, and the risk of overloading all depict the seriousness of this matter.

To maintain the longevity and efficiency of your AC compressor, it is crucial to always adhere to manufacturer instructions and industry standards. If you encounter any issues or need to make modifications, consult with an HVAC professional who possesses the knowledge and expertise to handle the task safely and effectively. Remember, the safe operation of your HVAC system is paramount for comfort and reliability in your home or business.


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