What Is an HVAC Hard Start Kit and Do I Need One?

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What Is an HVAC Hard Start Kit and Do I Need One?
Everything you need to know about HVAC hard start kits.

If you have an air conditioning system at home, you’ve surely heard of the term “HVAC hard start kit” before and you’ve most probably wondered if you need one.

What exactly is a hard start kit and how does it help your air conditioner at home?

Here’s the lowdown on everything you need to know about HVAC hard start kits, compressors, and the best long-term solution to your hard start problems.

What is a hard start kit?

A hard start kit is a start capacitor. It’s a device used to resolve an air conditioning system problem called hard starting. To understand how a hard start kit works, first you should have an idea how a compressor works during AC startup.

Essentially, the compressor is the heart of your air conditioner. It powers the AC. It’s the hardest working component of an AC unit. The moment it starts the cooling cycle, you usually hear its whirring sound.

As the compressor increases the pressure and the temperature on the refrigerant, the metering device reduces the same pressure and temperature on the refrigerant. Basically, the metering device is responsible for the amount of refrigerant that flows through the system.

A hard start kit does two important things for the air conditioning compressor:

  • It reduces the electricity used to power up the air conditioning system.
  • It reduces the startup period of the compressor.

Without a start capacitor, it takes the compressor four to eight times more electric current to start than to keep running. That surge of power causes the electric current to spike during startup, causing excess heat that may damage not just the compressor but other AC components as well. Old and worn units are especially prone to damages caused by electrical surges.

Without a start capacitor, the compressor has 50% torque efficiency, but with a hard start kit, torque efficiency drastically increases to 98%. With high efficiency, the compressor motor takes a shorter time to shift from start mode to run mode and the transition is smoother, prolonging the life of your cooling system.

Doesn’t it make sense then to install a start capacitor into the HVAC system? It does. In fact, manufacturers used to produce air conditioning units with built-in start capacitors, but the practice has been discontinued to decrease production costs.

What causes hard starting?

There are several reasons why an air conditioner experiences a hard starting problem. Knowing them may help you find the solution even before you call an expert in air conditioners.

The capacitor may have lost the ability to store temporary voltage for the motors of the unit. Without enough voltage, it can’t send enough power to the motors that start up the compressor and keep it running.

Heat does this to the capacitor, and when the capacitor starts failing, you will usually hear a clicking sound upon starting up your AC.

Worn down compressor motor due to loss of lubrication is another cause of hard starting. Without proper or enough lubrication, the compressor tightens up and has difficulty moving.

Hard starting may also be a sign that the air conditioner is worn down and ready for replacement. This can easily be discovered when you regular AC maintenance check-up. Sometimes replacing a hard starting air conditioning system is more cost-effective than getting it repaired over and over.

What are the signs of hard starting?

How do you know if your HVAC system is hard starting? What are the signs you need to look out for?

Short-cycling is one of the signs you should be aware of. When a compressor starts to short-cycle, it starts up, runs for a short time, then shuts off. This means the compressor doesn’t have enough stored energy to power the AC and cool the house.

If your AC is making louder noises than usual or if you hear clicking noises, that’s a sure indication that you need to call a top-rated HVAC contractor  ASAP. A service call will tell you that your AC may be hard starting.

Short cycling and too much strain on your compressor lead to a spike in electric consumption. Many customers have discovered that hard starting always means bigger electric bills.

Call your technician once your AC begins hard starting.

hard start kit

Who needs a hard start kit?

An air conditioner needs TLC just like about everything else in your home. Before your compressor starts showing signs of wear and tear, let HVAC experts service your AC for tuning up and maintenance.

Do you need a hard start kit?

You need a start kit if

  • you want to prolong the life of your air conditioner
  • your compressor is showing signs of hard starting
  • your circuit breaker trips
  • you want your AC to start smoothly even when there is low voltage or high head pressure, and
  • you want to avoid unnecessary repair and/or replacement expenses.

What are the different types of hard start kits?

Older AC models are usually equipped with start devices, but when they show signs of wearing down, a hard start kit may come in handy. For newer AC models without a built-in start kit, the compressor manufacturer or OEM usually specifies the type of capacitor suitable for the model.

It may be either one of the following:

PTC hard start kit

The PTC (positive temperature coefficient) is a 2-wire hard start kit that uses a ceramic component to remove the capacitor out of the circuit. As the PTC component heats up in less than a second, the capacitor is taken out. PTC kits are considered more convenient because of their 2-wire feature, which helps with easy installation.

MPR hard start kit

With the help of electro-motive force, the mechanical potential relay hard start kit takes the capacitor out of the circuit once the compressor is at 80% of its capacity. Most technicians find this kit more reliable thus it is often the recommended type.

If you have the phone number of an AC technician, give him or her a call so he or she can guide you in choosing the right hard start kit.

What are the benefits of a hard start kit?

A technician will tell you that the benefits of a hard start kit outweigh its disadvantages. With a hard start kit you

  • remove the strain of excessive electric current on your systems
  • prolong the life of your HVAC systems
  • significantly reduce electric consumption
  • decrease instances of flickering lights
  • avoid circuit breaker trips, and
  • avoid untimely repairs and replacements.

In essence, your air conditioner and/or heating device needs TLC. That is what a hard start kit is all about.

How much does a hard start kit cost?

A hard start kit is relatively inexpensive. When you look at repair and/or replacement costs, buying a hard start kit is the most sensible thing to do. It beats the cost of hiring an HVAC technician to service your cooling system, and for a small investment, you’re ensured you won’t have to deal with a hard starting problem.

Regular maintenance fees for cooling and heating services usually scare off customers, but an air conditioner needs maintenance services if you want it running inconsistent top condition. A hard start kit is one way of taking care of your AC.


The startup of an AC system is a complicated process that all takes place in seconds. Those seconds affect the way your cooling device works and ultimately affects the air quality in your home. The best part is, you can do something about it. Taking proactive steps to lessen the strain on your system will make a huge difference, so if you don’t have a hard start kit yet, it’s about time you get one.

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