What is an Air Conditioner Hard Start Kit

Put simply, an AC hard start kit is a capacitor — a device that collects and stores electricity ahead of time — that provides an air conditioning system with an extra boost of energy at startup. To understand why this is important, and how this device works, you first need to know a few basics about the main components of your HVAC system:

  • Refrigerant: Also called coolant, the refrigerant is a cold substance that is exceptional at cooling warm air. As the chilled liquid passes through the air conditioner’s evaporator coils, it absorbs heat and moisture from the surrounding air, lowering room temperatures significantly.
  • Compressor: An HVAC system’s compressor is responsible for pressurizing refrigerant and driving it through the special pipes that form a circuit between hot and cold areas. As a motor-driven pump, the compressor functions similarly to the heart, and without it, an air conditioner can’t function.
  • Evaporator: Generally located inside your home, the evaporator transfers cool air from refrigerant coils to the rest of the room.
  • Condenser: Carrying out the opposite function as the evaporator, the condenser captures heat from the home and vents it outside the home.
  • Fans: An air conditioning system uses fans, or blowers, to move cool air indoors and release hot air outside, usually via vents or ducts.

Between the compressor, fans and other components, HVAC systems need a lot of electricity for continuous operation. Older air conditioners, or systems where coolant pipes are too long, may use even more electricity to generate enough pressure to run correctly. In these situations, a hard start kit can make a huge difference in compressor functioning.          


How Does a Hard Start Kit Work?

Believe it or not, electric appliances and devices often use more energy during startup than afterward. That’s because it takes significant electricity for motors to go from a stopped position to the proper velocity. The startup can consume anywhere from four to eight times the amount of energy needed for normal operation. Once fans and pumps are spinning, it’s relatively easy and energy efficient to keep them moving at high speeds.  

So while the run capacitors that complement many compressors are excellent components, they’re not really equipped to handle the increased electrical requirements of startup. In other words, normal capacitors are excellent marathon runners, but poor sprinters. AC hard start kits are the opposite; they can handle the power surge from the first few seconds of a startup without breaking a sweat. Surge protectors can also help against this.

By storing an increased amount of electricity beforehand, hard start kits can get the compressor motor moving at an optimal speed almost instantly. The air-conditioner’s compressor doesn’t struggle, and your regular capacitor can take care of long-term operation without problems.


What Are the Advantages of a Hard Start Kit?

An air conditioning system relies heavily on the compressor to control home temperatures, especially in high-desert climates like those in Phoenix, AZ, where temperatures reach extreme levels in both directions. Depending on outside weather and thermostat settings, an air-conditioner’s compressor may turn on and off dozens of times throughout the day. After several years of operation, your HVAC may have stopped and started as many as 10,000 times or more! Here’s why having a hard start kit can keep your air conditioner in top shape over the years:

1. Extends Compressor Lifetime

The longer it takes for a compressor to reach run speed, and the more energy used, the hotter it gets. Excessive heat damages the motor’s wire coils, potentially causing them to burn out ahead of time. With a hard start kit near-instantaneous startup, the heat stays at a minimum and compressors last longer. For this reason, many manufacturers recommend installing a hard start kit even on new air conditioning system.

 2. Assists With Low Voltage Problems or Improper Wiring

Depending on the age of your home or the methods used during construction, wiring systems may be less than perfect. Improperly sized or worn wiring can lead to insufficient electricity for AC startup. A hard start kit can compensate for this type of low voltage problems.

 3. Provides Better Energy Efficiency

Even energy-efficient HVAC systems consume increased electricity when the compressor starts. Hard start kits use energy wisely — with an efficiency of approximately 98 percent — and reduce the total amount of electricity needed.

 4. Allows You To Avoid Compressor Replacement

 HVAC compressors are one of the most expensive parts in the system. While a hard start kit isn’t the answer to every compressor problem, it can keep the compressor working correctly where electrical issues are to blame. This can potentially save you a thousand dollars or more.


How Can You Tell When Your Air Conditioner Is Having Trouble Starting?

 Here are a few warning signs that can let you know it’s time to install a hard start kit:

 1. AC Tripped the Circuit Breaker

This issue can be caused by a compressor that is starting to wear. If the motor can’t supply the energy capacity needed for startup, the compressor will begin to draw higher amounts of power longer, tripping your home’s circuit breakers.

 2. AC Shows Flickering Lights

It’s normal for lights to flicker slightly when appliances turn on, but severe changes in lighting or power levels can indicate a problem. If an HVAC compressor is using excessive electricity, a hard start kit can help immensely.

3. The AC has Short Period of Operation Before Shutting Off

A customary cooling cycle should last around 15-20 minutes, depending on how warm it is outside and whether you have a single-stage or variable-speed HVAC system. What if you notice that your air conditioner is only operating in short bursts of a few minutes at a time? This is called short cycling, a potential indicator that something is causing excess energy strain on the system. If the problem is electrical, an AC hard start kit may be the solution.

 4. AC has Clicking Noises

Some clicking sounds from your A/C thermostat can be normal, while other clicking noises can happen because of a problem with your compressor, thermostat or fan. Sometimes the issue is within the components themselves, and other times it’s due to not having enough electricity to reach run speed. HVAC pros can tell the difference and may recommend a hard start kit to assist with power.

5. The AC is Making a Humming Noise

A constant electrical hum coming from your compressor likely means that it isn’t receiving sufficient power to turn the motor. This is a serious issue because continued electrical current will generate significant excess heat, leading to damage of the compressor or other systems.

If you suspect your air conditioner is having electrical problems, your first step should always be to call HVAC experts right away. Acting quickly reduces the possibility of damage to other air conditioning components.


Are Hard Start Capacitors a Permanent Solution?

Hard start kits are designed for long-term use, and high-quality models last for many years or even decades. Many HVAC systems benefit from installing a hard start kit from the very beginning of the operation. That way you receive energy savings immediately and provide maximum protection for your compressor. These kits are relatively inexpensive and often more than make up for the cost.

What if your HVAC system is already experiencing problems? Well, things aren’t quite as black and white when deciding whether or not to install a kit on a damaged compressor. However, if issues are caused by insufficient electrical current, a hard start kit can make a world of difference and revitalize the system.

Some compressor damage is mechanical in nature, usually caused by wear and tear over the years. In this case, while a kit would likely extend the compressor’s life for a while, some homeowners opt for system replacement instead. Of course, you don’t have to make the decision alone. If your air conditioner is experiencing startup issues, our HVAC experts at Day & Night Air can detect exactly what’s happening, clearly, explain the problem, and provide recommendations that help you make the best choice for your home and budget.


Is Professional Installation Needed for Hard Start Kits?

While the actual installation process of a hard start kit air conditioner isn’t overly complex, there are several reasons why it’s important to reach for the phone for a Day & Night professional instead of your toolbox when a hard start kit is needed:

  • Finding the Correct Size: Hard start kits and OEM start capacitors come in different sizes to meet the energy needs of your HVAC system. Installing one that’s too small for the compressor can be ineffective at best and damaging at worst, while a perfect fit keeps everything running smoothly for years.
  • Selecting the Best Kit: There are a few different types of hard start kits, including positive temperature coefficient (PTC) capacitors and 5-2-1 mechanical potential relays. PTC capacitors are usually cheaper and easier to install, but they don’t provide the same precision as 5-2-1 models, which operate the exact amount of time needed and then turn off. Mechanical potential relays offer better compressor protection and energy efficiency.  
  • Detecting the Real Problem: When it comes to your health, doctors are helpful because they can see a pattern in different symptoms and detect the underlying cause. In a similar way, HVAC professionals don’t just analyze surface issues. They figure out what component is causing problems and repair it correctly the first time.
  • Offering Long-Term Solutions: Our trustworthy professionals at Day & Night Air care about your satisfaction more than anything else. They can tell you whether installing a hard start kit makes economic sense for your HVAC system, or whether new AC installation may save you more money in the long run. The decision is yours, but our experts make sure you have all the information you need.


Taking good care of your compressor with an AC hard start kit can be a great idea. A smoothly operating HVAC system means your family gets to enjoy the perfect indoor climate all year round, especially in infamously-hot Phoenix. If you notice power problems or strange noises coming from your compressor, acting right away can prevent damage and ensure your family’s comfort. Contact Day & Night Air immediately for assistance or more information.