Is a Hard Start Kit a Good Substitute for a Capacitor for AC ?

Did you know it takes 5-10 times more energy to start an AC as it does to run it? That’s a lot of extra juice needed, and it has to come from somewhere. That’s the job of a capacitor – to store the extra electrical power needed to power a compressor into action.

A hard start capacitor kit is worth considering for an older AC or heat pump unit, especially one that is sluggish and won’t always start easily – or start at all.

Adding a hard start kit to your condensing unit – the outside unit in your HVAC system – can delay the need for system replacement by quite a few years.

What is a Hard Start Kit?

 As your air conditioning unit becomes older, some parts wear down and will need to be replaced.  One of the most common parts that require replacement are AC capacitors.  Rather than just replacing the capacitor, you can choose to install a hard start kit instead. The device allows your air conditioner to require less power when starting up. It also shortens the amount of time that it takes to start your air conditioner or compressor.

Terms time: An AC capacitor is also called a heat pump capacitor, condensing unit capacitor and, most commonly, simply a capacitor. And one of the most common hard start capacitor kits on the market is called a 5-2-1 hard start kit, so you will sometimes hear HVAC technicians refer to these units by that brand name, like calling tissue “Kleenex.”

Why use a hard start capacitor kit? Using a hard start kit compressor saver will allow your air conditioner to use up to 50% less energy to start the compressor. This energy saver reduces energy costs, but the real money saving is in extending the life of your compressor!

Get the right size kit! When purchasing a 5-2-1 compressor saver, you will have to buy a kit that will fit the size of your air conditioner.  For example, you can buy the hard start kids for 1-3 ton, 3.5-5 ton and 4-5 ton air conditioners. If you purchase a hard start kit that is not rated for your size of air conditioning unit, it may cause damage to the entire heating and cooling system.

Which is Better – A Hard Start Kit vs AC Capacitor?

If your air conditioner is having difficulty starting up or if you need to replace the AC capacitor, you will have a choice of whether to get a new capacitor or install a hard start kit in your condensing unit.  A hard start kit will save your air conditioner extra wear and tear since it significantly reduces the amount of energy needed to power the AC.  The price to hire an HVAC technician to install an AC capacitor or a hard start kit is basically the same for the labor costs.  AC hard start kit cost is given below.

Our recommendation: If your air conditioner is an older model then a hard start kit would be your best solution to allow your air conditioner to work more efficiently.  Although installing a hard start kit will enable your air conditioner to start up easier, over time a new compressor will most likely be needed – or you will need to replace the entire condensing unit. But as noted, a hard start kit addition can add years to compressor life.

Cost – How Much Does a Hard Start Kit Cost? AC Capacitor Cost?

A hard start kit or 5-2-1 compressor saver will cost anywhere between $15 to $75 for the kit.   You can purchase An AC capacitor that can cost you anywhere from $5 to $100 for just the actual capacitor.  This does not factor in any costs for hiring a professional HVAC technician to do the work if you decide not to attempt the installation process yourself.  Both an AC capacitor and a hard start kit will start around $100 for hiring the installation process out to an HVAC technician.

Is a Hard Start Kit Hard to Install?

If you have the proper tools and experience with connecting and working with electricity then you should be able to install a hard start kit yourself.  This will save you at least $100 in labor costs.  However, any installation that deals with electrical equipment should be done very carefully.  Installing a hard start kit is very similar to replacing an AC capacitor.  If you can install an AC capacitor, you can install a hard start kit.

Frequently asked questions

There’s more to learn about capacitor hard start kits. Here are common questions we get and their answers.

Why use a hard start kit instead of an AC adaptor?

If you have an aging air conditioner or if your air conditioner seems to struggle to start up, then a hard start kit might help prolong the life of your AC system plus make it work more effectively.  The hard start kit will allow your air conditioner to use less energy to start and therefore save your AC unit from extra wear and tear.

How much does it cost to buy a hard start kit?

You can buy a hard start kit from most big box home improvement stores and from many only sellers for anywhere between $35-$60, depending on what size of air conditioner you have at your home.  This is for the kit alone and does not include installation.

If you prefer pro installation, allow the HVAC technician to choose the best kit for your condensing unit.

How much does it cost to install a hard start kit?

If you decide that installing a hard start kit isn’t something you can comfortably do, then you will need to hire an HVAC technician to do the work.  On average you can expect to pay between $100-$175 for the labor to install the hard start kit.  The total cost for the kit and the labor ranges from $135-$250 for the entire project.

What is a 5-2-1 hard start kit? What is a Dometic hard start kit?

A 5-2-1 compressor saver and a hard start kit is the same thing, just a different way of describing it.  5-2-1 often refers to how to properly connect the various terminals and wires when installing the 5-2-1 kit.

A Dometic hard start kit is a popular brand used by homeowners and HVAC technicians.

How much money can I save by installing a hard start kit?

The answer to this question is twofold.  First of all, installing a hard start kit on your air conditioning unit can save up to 15% on the energy costs for your HVAC system.  Also, a hard start kit can prolong the life of your air conditioning system. This will save you money in the short term, but eventually you will need to either replace the compressor or the entire air conditioning system.

Can a hard start kit damage your air conditioning system?

While using a hard start kit can prolong the life of your air conditioning, it can also cause some possible damage to the compressor with continued usage.  The reason is due to the fact that a hard start kit will send too much current for too long to start the compressor. This surge in electrical current can possibly burn out the wires or connections. Make sure you have the right part for the size of your condensing unit. For example, if you install a kit designed for a 5-ton condensing unit, it might have too much “juice” for a 2.5 or 3-ton system.

How can I tell how large my condensing unit is? What is the size of the AC?

Find the model number, and the numbers in it will give a clue. Two of them will refer to the number of BTUs, and 12,000 BTUs equal 1 ton. So, look for these numbers, and here is what they mean.

  • 18 = 1.5 tons
  • 24 = 2.0 tons
  • 32 = 2.5 tons
  • 36 = 3 tons
  • 42 = 3.5 tons
  • 48 = 4 tons
  • 60 = 5 tons

For example, the Rheem RA1624AJ1NBRHC is a 2-ton unit (see the 24?), and the RA1648AJ1NA is a 4-ton unit (see the 48?). The “16” number refers to the efficiency of the units – 16 SEER.

Will a hard start kit work in a heat pump? Will a hard start kit work in a package unit?

Yes – both heat pumps and package systems have compressors, so using a hard start kit can assist those compressors in starting by using less electricity.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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