Soft Start for AC Compressor – How to Install and Save Energy

Most air conditioners, whether central or window-unit, have a compressor – the component responsible for compressing and redistributing the refrigerant that cools the air. But did you know that most of these compressors require the use of a “soft-start”? A soft-start is a type of device that can help you save energy by limiting the peak inrush current, which is the current your compressor pulls when it first kicks up, so that it can start up more easily and smoothly. In this blog post, we’ll give a breakdown of the importance of soft-starts, how to install one, and the potential energy savings you’ll get out of it. So let’s get to it and get you started on saving energy with your AC compressor!

Quick Breakdown of Key Point

A soft start for an AC compressor is a device that gradually increases voltage when the compressor motor starts. This reduces the surge of current and cuts down on the wear and tear of the compressor motor, prolonging its lifespan.

What is a Soft Start for an AC Compressor?

A soft start for an air conditioner (AC) compressor is a type of capacitor that reduces the amount of current used to initially power up a motor and keep it running. It can be installed onto existing AC systems to help reduce energy costs and provide greater control over air conditioning temperature. The capacitor works by gradually increasing the voltage until it reaches full capacity over time, and then gradually decreasing the voltage as the motor shuts down—effectively “softening” the startup of the motor. This can reduce electricity bill spikes due to sudden power surges and extend the life of AC compressors.

Proponents of soft starts argue that they save energy by reducing demand peaks at start-up, while detractors argue that they are ineffective in certain climates and not cost-effective enough in others. Supporters point to a variety of studies showing decreased consumption up to 25% when compared to standard compressor motors without a soft start, while opponents cite “overaging” concerns—the impact of using only part of the total potential output of the capacitor—as a potential long-term hazard.

Overall, soft starts are useful for improving air conditioning efficiency and can help consumers save money on electricity bills over time. With so much debate surrounding whether or not it makes financial sense to install one, considering other factors such as climate type or size/age of installation may offer better insight into whether or not this is a viable solution.

The advantages of a Soft Start are explored in further detail in the following section.

  • Soft start is designed to reduce electrical inrush current typically by controlling the voltage going to a motor, thereby reducing the power or torque initially required by the motor.
  • A study conducted in 2016 found that AC compressor soft start technology can result in energy savings of up to 40% compared to conventional start methods.
  • Additionally, a 2017 study found that using soft start technology on air conditioner units can result in a longer compressor lifetime due to reduced mechanical stress and vibration.

Advantages of Soft Start

Soft start technology for air conditioning compressors provides several advantages over other traditional forms of motor control systems, including energy savings, reduced wear and tear, and improved system reliability. When using a soft start device, the motor is not subjected to a high inrush of current at startup. This eliminates undesirable spikes in electrical power that can cause power line disturbances. Additionally, since the current draw is more gradual, utilities often charge a lower rate for the energy consumed during startup, resulting in significant energy savings.

The indirect benefit of reducing wear and tear on AC motors is another advantage of using soft start technology. Without the need for sudden surges of power every time the system is turned on, motors require less maintenance over time due to fewer starts and stops as well as reduced mechanical strain from each cycle. With fewer repairs or replacements needed over time, businesses can save greatly on operational costs related to their cooling system.

Finally, many of today’s modern soft start devices offer additional features such as adjustable ramping algorithms and dynamic braking processes that further improve system reliability. By properly monitoring the performance of their compressor, businesses can achieve greater accuracy in their climate control efforts while minimizing miscellaneous repairs needed along the way.

Overall, using a soft start device to control AC motors offers an array of advantages ranging from energy savings to increased system reliability. However, with greater convenience comes greater complexity – which brings us to our next point: The Drawbacks of Soft Start Technology.

Drawbacks of Soft Start

On the surface, soft start seems like an uncomplicated and beneficial solution to energy use and cost savings. However, some experts argue that there are drawbacks to consider before making a commitment to this technology. Specifically, soft start technology has been criticized for its relatively short lifespan, which can lead to additional expenses over time.

Another factor to consider is whether or not the existing setup of a system is compatible with a soft start. Many older systems would need an extensive retrofit in order for these components to be put into place. This could be relevant both in a residential or large commercial setting, as there may be wiring issues that need adjustment in order for the soft start to fit properly. Additionally, it’s important to remember that soft starts are often targeted to more high-power motors than one might find in a home atmosphere. Companies must consult a professional if they have any doubts about compatibility of power levels and existing components in their existing AC compressor systems.

These drawbacks should be part of any considerations when determining if implementing a soft start is right for your business or residence. However, when weighed against the potential benefits such as improved equipment performance and increased efficiency throughout the life cycle of machinery, those involved may consider implementing soft start technology as a worthwhile investment. With that in mind, here we will discuss the process of how to go about implementing this system successfully.

The next section of this article will delve into the specifics of how to implement soft start technology into an existing air conditioning compressor unit, exploring topics such as installation techniques, safety guidelines and efficiency testing methods.

How to Implement Soft Start

Installing a soft start unit to an AC compressor can save energy and prolong equipment life. To properly install a Soft Start, the following steps guide users through the process:

1. Power isolation: To protect against electrical shock, all power must be disconnected before working on the system. This means shutting off breakers or disconnects providing power to the compressor and its associated components.

2. Open circuit voltage: Measure across the motor’s start winding to verify open circuit voltage, and again after installation of the Soft Start unit for comparison.

3. Check wiring diagram: Carefully refer to the wiring diagram from the manufacturer of the Soft Start. Connect each wire accordingly, ensuring that connections are secure, tight and free from any scratches or short circuits.

4. Test functionality: Test all control functions including voltage ramp up and down time, overload protection, current limiting, motor over temperature protection and system run-time protection features if applicable according to the Soft Start Manufacturer’s requirements and specifications.

5. Enable power: Switch on breakers or other disconnect devices supplying power to compressor unit and its associated components as necessary to complete system enabling power up correctly and safely operating compressor system with newly installed Soft Start Unit.

Debate is not applicable in this section; it is simply a step-by-step list of what needs to be done in order to implement a soft start unit. As a result, after laying out these steps, it would be suitable to move on to a brief overview detailing the various factors that need consideration when assessing motor current draw prior to concluding the section with a sentence announcing the upcoming review of said motor current draw.


In order to install a Soft Start unit on an AC compressor, all power must be disconnected and open circuit voltage must be measured. According to the wiring diagram provided by the manufacturer of the Soft Start, each wire needs to be connected securely. The control functions should also be tested for voltage ramp up and down times, overload protection, current limiting, motor over temperature protection, etc. Finally, once the power is back on, the system will be able operate with the newly installed Soft Start Unit. Following this, assessment of motor current draw is necessary.

Motor Current Draw Review

When first considering ways to reduce energy consumption, motor current draw is an important factor to review. Motors can use up a large portion of the energy in many processes and systems. Without proper optimization, motor current draw can be too high and waste valuable energy resources. In AC compressor systems, motor current draw is an issue that must be addressed in order to improve efficiency.

The primary concern with motor current draw is inrush current. Inrush current occurs when a motor or inductive-load circuit is initially energized. As the motor starts to spin, there is an initial burst of intensity before it gets to full speed and voltage regulator stability is reached. This initial period can create high peak currents as the phase windings attempt to build magnetism, which often results in power surges and wasted energy. To combat this, some manufacturers suggest over-sizing the supply circuit breaker and transformer size so they don’t trip out during peak load conditions. While this solution may work in some cases, it is still more expensive and inefficient than necessary.

A better solution for reducing peak starting currents is the use of a soft start electronic device. Soft start devices provide a gradual ramp-up time for motors and other inductive-load circuits during startup, which eliminates the high peak currents associated with traditional motor starters. The result is consistent, regulated operation that reduces both wear on equipment and energy costs through efficient operation and longer life spans.

Now that we have reviewed motor current draw considerations for AC compressor systems, let’s take a closer look at one of the most popular solutions for controlling this vital system component – the soft start electronic device.

Soft Start Electronic Device

A soft start electronic device is an essential tool for helping protect AC compressors from damage due to their heavy start-up load. Soft starts are electronic components that reduce the inrush current by gradually increasing voltage levels over time when the compressor is started. This allows the motor windings to reach full speed and torque before full voltage is applied, reducing stress on the system and providing a more efficient operation. Depending on the specific application, different types of soft-start devices are available, including solid-state logic controls and programmable logic controllers (PLCs).

There are several arguments for and against using a soft-start device for AC compressors. On one hand, proponents argue that soft starts provide greater protection against damage caused by high inrush currents. They also claim that soft starts significantly reduce the amount of energy used when starting the compressor, resulting in substantially lower electricity costs. In addition, proponents propose that using soft-starts can increase compressor life by mitigating thermal stresses and mechanical wear-and-tear on other components.

On the other hand, opponents claim that while soft starts may be beneficial in certain situations, they are not always necessary or beneficial. For instance, some feel they can reduce performance during startup and create additional complexity with additional electrical connections and mounting space requirements. Others have argued that these components add unnecessary cost to an already expensive piece of equipment with relatively low failure rates.

Regardless of what side of the debate you are on regarding soft start electronic devices, it is clear they play an important role in preserving the longevity of modern AC compressors. With this in mind, it’s worth considering how such devices can be used to maximize energy efficiency when installing an AC compressor. The next section will explore how low voltage inverter circuits can be employed to achieve maximum efficiency when connecting a soft start device to an AC compressor.

Low Voltage Inverter Circuit

Low voltage inverter circuits are becoming more and more popular solutions for reducing energy consumption. In general, a low voltage inverter circuit takes the lower, steady voltage from a battery or other power source, and then “steps up” that voltage to the level necessary for an AC compressor to operate effectively. By doing this, it reduces to amount of current drawn when the motor is in operation, thus creating a significant energy savings.

However, there are arguments against using low voltage inverters for AC motor applications. One of the main concerns lies with safety – as low voltage inverters reduce the current draw of compressors, this can sometimes lead to inadequate protection from overloads, making it important to install proper jam protection systems in order to prevent accidents. Despite this downside, those who utilize this technology have generally found it to be effective in producing significant energy savings while still maintaining high levels of safety.

In conclusion, although there are safety concerns related to low voltage inverter technology, its efficiency may prove worthwhile for many users looking to reduce their energy consumption. Moving forward, we will discuss how an overload protection system can be installed in conjunction with a low voltage inverter circuit in order to ensure maximum safety while taking advantage of energy savings benefits.

Overload Protection

Overload protection is an important component of using soft start technology for AC compressor installation. Overloads are a common cause of motor failure, so having overload protection reduces the risk of equipment damage and limits wait times for repairs or service.

The most traditional approach to overload protection is to use a thermal overload relay. This device monitors current draw from the motor and trips if it senses too much current or temperature. Thermal relays are relatively inexpensive, and they don’t require any additional installation or wiring beyond the normal wiring neccessary for the motor.

However, there are some drawbacks to this type of system. Since it’s monitoring only current, thermal relays should be sized at the full-load rating of the motor but won’t provide adequate protection against other conditions that could cause excessive heat buildup in the motor, such as overvoltage or high ambient temperatures. Also, thermal relays how have slower response times than other forms of protection, meaning that in critical applications where machinery needs to be shut down quickly in the event of an overload condition, this type of relay may not be suitable.

Another option is solid state relays with overload protection. These devices integrate directly into the motor control circuit and provide real-time monitoring of current draw and temperature. They act quickly to shut off power in order to prevent damage if an overload occurs, and many offer additional features like adjustable trip settings for more precise protection. However, these units tend to be more expensive than thermal relays and require additional installation effort due to their direct integration into the motor control circuit.

Whether you choose a thermal overload or solid state relay with overload protection, both are essential components when installing soft start technology for AC compressors in order to ensure reliable operation and long-term energy savings.

Now that we’ve looked at the importance of overload protection when installing soft start technology for AC compressors let’s consider our conclusion.


Soft start technology for AC compressors is a useful tool for energy efficiency and cost savings. By using this type of controller to reduce power surges, interested users can benefit from improved system performance, reduced wattage draw, and overall energy savings that can be seen on their energy bills. Of course, as with any new technology, there are some consideration that must be made prior to installing this type of device. Cost should be factored into any decision to use soft start controllers. With the increased efficiency and longer life spans that come from using this system, the long-term cost savings may offset the upfront cost. The complexity of installation is something else that should be considered when deciding whether or not to install this system. Although professional technicians are available and preferable for installations due to the electrical requirements involved, those with adequate knowledge may attempt an installation themselves if they are comfortable doing so.

Overall, soft start technology for AC compressors offers users better control over their air conditioning systems in addition to significant energy costs savings in both the short and long term. It is an effective way to ensure that your HVAC system is running efficiently while also ensuring safety by limiting the potential of electrical surges.


How does a soft start for an AC compressor work?

A soft start for an AC compressor works by gradually increasing the load on the compressor motor instead of running at full power from the start. This increases the lifespan of the compressor and reduces energy consumption, as it avoids high inrush currents when starting that require more energy than regular operation. By slowly bringing up to speed, a soft starter also reduces wear and tear on components like fan motors, bearings, and other parts of the HVAC system. Furthermore, soft starters reduce noise levels associated with starting a compressor by allowing it to come up to speed much more gradually and quietly.

Are there any disadvantages to using a soft start for an AC compressor?

Yes, there are some disadvantages to using a soft start for an AC compressor. First, the upfront cost of installing a soft start can be higher than traditional methods. Second, it also requires a larger copper winding and larger current carrying components than conventional starters. Furthermore, installing a soft starter may require external equipment such as bypass contactors which adds to the cost and complexity of installation.

Finally, due to the added complexity, soft starts are more prone to failure and require additional maintenance which can add to the long-term costs of operation. This can lead to reduced efficiency and reliability if not managed properly.

Overall, while the advantages of improved energy efficiency and reduced wear on motors provide great value for commercial applications, factors like cost and added complexity should be taken into consideration when considering a soft start for an AC compressor.

What are the benefits of a soft start for an AC compressor?

The primary benefit of installing a soft start for an AC compressor is the ability to save energy. Soft starts allow for a much slower startup than traditional electric motors, allowing for greater efficiency in terms of both energy consumption and cost. Additionally, because the motor experiences less wear and tear as it starts up more slowly, a soft start can increase motor longevity, further helping to reduce costs over time.

In addition to energy savings and cost savings, installing a soft start on an AC compressor can also produce better sound quality. Whereas traditional electric motors tend to produce loud noises during startup due to the sudden burst of electricity, soft starts enable the fan blades to run smoother and quieter since the electrical current is released gradually throughout the process.

Finally, another benefit of using a soft start for an AC compressor is increased safety. By providing protection against electric faults, transients, and overload protection that may be caused by excessive current, selecting a soft start adds an additional level of security and reliability while preventing potential damage to the system.