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Hard Start Kits: What are they, and why would you need one for your HVAC?

Hard Start Kits: What are they, and why would you need one for your HVAC?
Olivia Minnier
Content Writer

About This Article

In this article, we discuss what a hard start kit is, why you might need one for your air conditioner, and steps you can take if you need one for your system.

Is the compressor on your air conditioning system no longer working? Is your capacitor worn out from damage? If so, a hard start kit might be an excellent solution to look into to preserve the life of your system until you’re ready to replace it.

An influx of electricity like the kind that occurs during a power surge or a storm can wreak havoc on your HVAC system and damage certain parts, like the compressor and capacitor.

First, we will go over a hard start kit and how it can be helpful in these situations.

What is a Hard Start Kit?

A hard start kit adds the starting torque and some means of removing the capacitor from the start circuit as soon as the compressor has started.

It helps to aid the starting process of air conditioners and heat pumps. Hard start kits accomplish two goals:

  • Stores the energy
  • Diverts any excess energy preventing damage

Why do I need a Hard Start kit for my HVAC system?

A hard start kit on a single-stage air conditioner or a heat pump can reduce the strain on your system to start up by as much as 50%. Having a hard start kit can also prolong the life of your system, so we recommend it for every new single-stage air conditioner or heat pump. If you have an older system that is reaching the end of its life span, a hard start kit can also prolong the life of your system by a few additional years.

What are the Different Types of Air Conditioners?

There are three types of air conditioners: single-stage, two-stage, and variable speed.

As the different names imply, a single stage is either 100% on or off, and a two-stage air conditioner is more efficient than a single stage in that it can run at a lower level. So it has 100% on and a slightly lower speed. By comparison, a variable-speed air conditioner can have up to 700 distinct compressor settings corresponding to varying airflow levels.

The two-stage, while superior to the single-stage compressor in terms of efficiency and options, pales compared to the variable speed.

You’ve probably heard of SEER Rating and how it’s a measure of efficiency. Variable-speed air conditioners are when you get to 20 or more SEER rating, which is top of the line for central air systems.

Similar to how the two-stage can operate at a lower speed when it doesn’t need to be at 100%, a variable-speed system can adjust accordingly to use only the power required to maintain a consistent temperature in your home.

Pros and Cons of One-Stage AC


The big one here is probably obvious: the initial price.

Single-stage air conditioners will be the cheapest to purchase and install. If you’re on a budget, this is probably your best bet. The good news is that a one-stage AC is still going to cool your home adequately, provided it’s sized properly and installed correctly. So you don’t have to worry about that front.


The cons are mostly related to efficiency and long-term costs. Your energy bills will be higher since it uses 100% of its power 100% of the time it’s on. While modern systems tend to run very quietly, the start and stop of the air conditioner can also be an annoyance to some.

Pros and Cons of Two-Stage AC

Based on the previous information about a single-stage AC, you can probably see where this is going. Two-stage air conditioners are going to provide more efficiency compared to single-stage air conditioners.

These units are a nice middle ground between low-end and high-end efficiency and initial cost and will save you on energy costs compared to a single-stage.

Think of it like gas mileage. It’s more efficient to drive at slower speeds than higher speeds, and slamming the pedal can produce long-term wear and tear on your car. The benefits of having a second, slower stage are somewhat similar in terms of efficiency and system usage.

Depending on the model, brand, and other factors like the size of your home, the initial price tag can be closer to single-stage or variable-speed, so you’ll want to consult with an HVAC professional before determining if this is right for your budget.

Pros and Cons of Variable-Speed AC


Variable-speed air conditioners are the Cadillacs of central air cooling. They’re going to run the most efficiently and will generally be the quietest as well since they’re often operating as low as 40% of their maximum power capacity.

You’re also going to save the most on energy costs and have the most significant degree of control over the temperature in your home. You’ll experience fewer temperature spikes, like when single-stage systems or even two-stage systems turn on and off.

With a variable-speed AC, your home will be more consistently comfortable.


The primary downside is the initial cost. They are not very affordable for the initial cost, even if they make up that cost in the long run.

The other downside is also related to cost, but regarding repairs. If a part breaks, it can be costly regardless of the system. But the advanced technology inside a variable-speed air conditioner can often incur increased replacement costs and labor costs.

Even if a system is under warranty, most don’t cover labor costs, so you can still be on the hook for more than expected, depending on the repair. Be prepared to discuss this with your HVAC partner before installing this system.

Why can’t a Hard Start Kit be Used for a Variable Speed or a Two-Stage Air Conditioner?

It can’t be used on a variable stage or two stage because of the way they operate and function. These units do not need a hard start kit because they have a different electrical configuration than a single-stage AC or a heat pump.

 However, there are a few use cases where a hard start kit can be beneficial.

Best Use Cases for a Hard Start Kit

  1. If your air conditioner appears to be hard starting already

If your air conditioner is already hard starting, you might need a hard start kit on your system. But how do you know if your system is hard starting? If you notice any of the following, you might have a system that isn’t running as smoothly as it should.

  • If you hear your AC, start then shut off quickly after it turns on
  • A clicking noise is coming from the compressor
  • The compressor is tripping the circuit breaker in your home
  • Lights in your home flicker when your AC starts up

AC shuts off after starting

If you hear your AC shutting off shortly after it starts up, this is an issue with HVAC units called short cycling. It is when your unit becomes “stuck” in the start-up cycle and can cause a lot of wear and tear to the compressor and the unit's health.

Clicking noise from the compressor

If you hear a clicking noise coming from the compressor, that likely means it is trying to use too much power to turn on the unit. This can wear down your system fast.

The compressor is tripping a circuit breaker

If you notice the circuit breaker in your home tripping, this is also a sign it is using too much power to turn on. Your circuit breaker is tripping to prevent any damage.

Lights Flickering inside your home when the AC starts

If the lights start flickering when the AC starts up, this is another sign of hard starting if you notice a very dramatic flickering happening inside your home.

Another scenario where a hard start kit could be useful isn’t related to a problem at all.

  1. If you have a new air conditioner or heat pump that is a non-variable speed unit

Manufacturers used to provide hard start kits with new models of units, but newer models frequently do not include one. It helps reduce the wear and tear on your system over time and keeps it running smoothly.

All of these are likely situations when you might need a hard start kit. If you are experiencing any of these issues in your home, it is time to place a call to your HVAC technician.

As with any other repair or upgrade to an appliance in your home, you’re likely worried about how much it’s going to cost.

How Much Does a Hard Start Kit Cost?

To have a hard start kit installed on your compressor, you can expect to pay anywhere from $300 to $350. Our prices always include the cost of labor and parts. The overall price of a hard start kit is cheaper than paying for a compressor replacement which can be $2,500 or even more.

With that being said if a compressor replacement is so common, why isn't it included with the purchase of a system?

Why isn’t a Hard Start Kit Included With New Equipment?

A hard start kit is typically not included with a new system because it is not needed until the equipment fails. Your air conditioner and heat pump will generally work without one. Manufacturer’s frequently will not include them with their products so that they can sell more units and keep their costs down.

If the manufacturers don’t typically include hard start kits, it might be hard to determine who the intended audience is for the product or think they’re just for maintenance pros or DIY’ers.

Who Should Buy a Hard Start Kit?

At Fire and Ice, we recommend that a hard start kit be included with all new purchases of a heat pump and every single-stage air conditioner.

A single-stage air conditioner is either 100% on or 100% off; there is no in-between. Variable-speed air conditioners start at 35% power and go up to 100% based on the outdoor temperature where the condenser unit is located, the indoor temperature, and the needed run time.

Next Steps for your HVAC Hard Start Kit

If you are having issues with your air conditioner compressor or heat pump or are the new owner of one and want to take the next step towards getting a hard start kit and live in the Columbus, Ohio area, give us a call. We are ready to answer any questions you might have about your heat pump or HVAC system.

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