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AC outdoor unit compressor

If you are unfamiliar with HVAC systems, it can be easy to overlook the importance of efficiency. However, improving the efficiency of your HVAC system can save you money on your energy bills and extend the lifespan of your unit.

One way to improve HVAC efficiency is through the use of a Hard Start Kit for AC.

What is a Hard Start Kit?

A hard start kit is an electrical component that helps your HVAC system start up more efficiently. When an AC unit starts up, it draws a large amount of electrical current to get the compressor running. This can cause strain on the compressor and increase the amount of time it takes for the unit to start up.

A hard start kit for AC helps to reduce this strain by providing an extra boost of power to the compressor during startup. This can reduce the amount of time it takes for the compressor to start running, which can increase the overall efficiency of your HVAC system.

Types of HVAC Hard Start Kits

There are two main types of HVAC Hard Start Kits: potential relay kits and Positive Temperature Coefficient (PTC).

Potential Relay Hard Start Kit

A potential relay start kit includes a potential relay, which is a type of electromechanical device that senses the voltage across the start winding of the compressor during startup.

When the compressor is starting up, the potential relay closes its contacts and allows the start capacitor to assist in the startup process. Once the compressor reaches its running speed, the potential relay opens its contacts and takes the start capacitor out of the circuit.

This type of AC hard start kit is suitable for older air conditioning units that have single-stage compressors. It can help overcome the challenges of hard starting that may arise due to factors such as aging compressors, low voltage, or long refrigerant lines.

These start kits provide a cost-effective solution to improve the startup reliability and performance of older AC units, extending their lifespan and reducing the risk of compressor damage.

Positive Temperature Coefficient (PTC) Hard Start Kit

A Positive Temperature Coefficient (PTC) resistor hard start kit is an electrical device designed to provide a temporary boost of power during the initial startup phase of the compressor, which can help overcome challenges such as high pressure or low voltage conditions that may hinder the compressor from starting smoothly.

The main component of a PTC resistor hard start kit is the PTC thermistor itself. It’s a type of resistor that changes its resistance with temperature and a relay.

When the air conditioning system is turned on, the PTC thermistor in the hard start kit is cold and has a low resistance. This allows a high amount of current to flow through it and energizes the relay.

The relay then connects an additional capacitor in parallel with the compressor’s run capacitor. This increases the overall capacitance in the circuit, providing an extra boost of energy to the compressor during startup.

As the PTC thermistor heats up due to the current flow, its resistance increases gradually. This reduces the current flowing through the relay and eventually turns it off.

Once the compressor has started and is running smoothly, the PTC thermistor reaches a higher temperature and settles at a higher resistance, allowing only a small amount of current to flow through it.

The relay disconnects the additional capacitor, and the compressor continues to operate using its regular run capacitor.

These kits are suitable for single-phase air conditioners and systems with thermal expansion valves or low-voltage.

How Hard Start Kits Work

To fully grasp how a hard start kit works, it’s important to first understand the startup process of an HVAC unit. When an HVAC unit is turned on, the compressor must start running in order to begin cooling the air. However, the compressor requires a large amount of electrical current to start running.

During startup, the compressor’s motor windings create a magnetic field that pulls the rotor into motion. This motion generates a back electromotive force (EMF) that opposes the current flowing through the motor windings. This opposition to the current can cause the compressor to struggle to start up, resulting in increased strain on the unit.

This is where an AC hard start kit comes in. By providing an extra boost of power to the compressor during startup, a hard start kit can help the compressor overcome the initial resistance and start running more efficiently.

The potential relay in a hard start kit plays a key role in this process. It senses the back EMF generated by the compressor and switches the start capacitor out of the circuit once the compressor is up to speed. This allows the compressor to run more efficiently, reducing strain and improving overall performance.

Benefits of Hard Start Kits for AC

HVAC system

There are several benefits to installing a hard start kit in your HVAC system. Some of the most significant benefits include:

Improved Energy Efficiency

When an HVAC system’s compressor struggles to start up, it often requires more power than it would if it were operating normally. This can lead to increased energy consumption and higher electricity bills.

A hard start kit can help reduce the amount of power needed to start the compressor, allowing the system to operate more efficiently. This also means less energy is consumed during the startup process, which can lead to lower utility bills and reduced energy consumption over time.

Increased Lifespan of Compressor

A compressor that has trouble starting can put significant strain on the motor and other components. Over time, this strain can cause wear and tear, leading to premature failure.

An AC hard start kit can help reduce the strain on the compressor by providing an extra boost of power when it starts up. This can help prevent damage and extend the compressor’s lifespan, saving homeowners and businesses a significant amount of money in repair and replacement costs.

Reduced Noise

When a compressor struggles to start up, it can create a lot of noise and vibration. A hard start kit can help reduce this noise and vibration, making your HVAC system quieter and more comfortable to use.

Improved Cooling and Heating

With a hard start kit, your HVAC system can start up more quickly and efficiently, allowing it to cool or heat your home more effectively. This means you can enjoy a more comfortable indoor environment, regardless of the weather outside.

Reduced Maintenance Costs

Since hard start kits help reduce the strain on the compressor, they can help prevent damage to other components, reducing the need for maintenance and repairs. This can save homeowners and businesses both time and money in the long run.

Installation of AC Hard Start Kits

Installing a hard start kit for AC is a relatively straightforward process, but following the manufacturer’s instructions carefully is essential.

Here are the basic steps involved in installing a hard start kit:

  1. Shut off the power to your air conditioning system at the circuit breaker.
  2. Locate the capacitor on the outside of the condensing unit and discharge it by shorting out the terminals with a screwdriver or other metal object.
  3. Remove the wires from the capacitor and disconnect them from the mounting bracket.
  4. Once the old capacitor is removed, you can install the new hard start kit in its place. Start by attaching the mounting bracket to the same location where the old capacitor was mounted.
  5. Connect the wires from the potential relay to the compressor motor and the wires from the start capacitor to the potential relay.
  6. When this is done, connect the remaining wires to the power source and turn the power back on at the circuit breaker.

Before testing the system, give it a few minutes to allow the compressor to cool down. Then, turn on the air conditioner and listen for any unusual sounds or vibrations. If everything sounds normal, you’ve successfully installed a hard start kit and should enjoy a more reliable starting performance from your AC unit.

Factors To Consider When Selecting a Hard Start Kit

When choosing the right hard start kit for your HVAC, here are several factors to consider.

Compatibility with HVAC system

You need to ensure that the hard start kit you choose is compatible with your HVAC system. You should consult the manufacturer’s specifications to determine whether a particular hard start kit is appropriate for your system.

Size and Power Rating Requirements

The size and power rating of the hard start kit should be appropriate for the size and power rating of your compressor. If the kit is too small, it may not provide enough power to start the compressor. If it’s too large, it may overload the compressor or cause other problems.

Types of Hard Start Kits Available

There are several types of hard start kits available. Each type has its own pros and cons, so it’s important to research and choose the one that is best suited to your specific needs.

If you’re not sure which type is the best for you, consider talking to an HVAC professional to help you out.

Professional Installation vs. DIY Installation

Installing a hard start kit can be a complex process, and if not done correctly, it can cause damage to your HVAC system.

We’d generally recommend having a professional install the kit to ensure that it is done correctly and safely. Meadow Air technicians are only a phone call away. If you need them.

However, if you are comfortable working with HVAC systems and have experience with electrical wiring, you may be able to install the kit yourself. Just be sure to follow all instructions carefully and take appropriate safety precautions.


HVAC hard start kits offer several benefits, including reducing energy consumption, minimizing compressor wear, and extending the lifespan of the HVAC system. These kits can help the system start up more efficiently, decrease the amount of time the compressor is under stress, and improve overall performance.

Choosing the right hard start kit for your system and having it installed by a qualified technician to ensure proper functionality is essential. Regular maintenance and care for the hard start kit is also critical for its longevity and effectiveness.