Air Conditioning Basics: The Beginner’s Guide to Choosing an AC Unit

Shannon Llewellyn
Updated July 9, 2021
woman with cup of coffee near large windows and underneath air conditioning vent
chee gin tan/E+ via Getty Images

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There’s nothing better than relaxing in your air-conditioned home on a hot summer day. But have you ever wondered how air conditioning works to cool your home or what types of AC units are available? Learn air conditioning basics in this beginner’s guide to everything AC.

How Does Air Conditioning Work?

The science of air conditioning has come a long way. The first electric powered residential air conditioners stood 7 feet high and were 20 feet wide, which, nowadays, is the size of a walk-in closet. And long gone are the scary R-22 type refrigerants, aka freon and CFCss (chlorofluorocarbons), that were found to contribute to the depletion of the ozone layer. Today’s breed of HVAC systems rely on non-ozone depleting refrigerants.

Regardless of brand or size, modern day air conditioning works by this simple concept:

  •  Warm air is drawn in and blows over the cold evaporator coils

  • The compressor raises the refrigerant temperature

  •  As the internal heat is transferred outside, the refrigerant gets cold and pumps cold air inside

Thankfully, today’s air conditioners are sleeker, quieter, and more energy-efficient. Better yet, there’s a style, size, and functionality for every living space and budget.

What Types of AC Units Are Available?

You can wipe the sweat off your brow because there really is a great air conditioner for every living situation. If you’re still on the fence about which route to take, reach out to an HVAC specialist for some solid direction. They’ll be much more knowledgeable than any online AC retailer.

Here’s a look at the types of air conditioners you’ll be able to choose from when shopping for your home.

Window Mounted Air Conditioners

Window mounted air conditioners are the least expensive way to get some relief from the heat. They can effectively cool 1 or 2 rooms, and can be stored in a box or wrapped in plastic when they aren’t needed. The average cost to run a window air conditioner is $0.06 to $0.88 per hour at $0.13 kWh. Installing a window AC unit costs between $150 to $500. What’s great about this option is if you move, you can bring them with you.

Wall Installed Air Conditioners

Call an HVAC professional for this one since permanent installations through the wall require expertise. The initial investment for installing a wall unit air conditioner is obviously higher than simply putting in a few brackets like its window mounted partner. But the benefits in long-term energy savings definitely makes up for it in the long run. Expect to pay between $400 to $700, not counting professional installation.

Portable Air Conditioners

Standing portable air conditioners are great if you want to take cool air with you from room to room. Outfitted with HEPA filters, varying temperature settings, and oscillation features, portable air conditioners are powerful enough to not only cool the air, but clean it. 

Portable air conditioners are great for infants’ rooms or people whose immune systems are compromised because they clean and recirculate the air. Models range between $250 to $500 and some use replaceable filters. Do your research before buying the model that works best for you.

Ductless Mini-Splits

‘Mini-split ACs' work the same way a central air conditioning system would work, only without the ducts. Ductless mini-splits require installation so don’t attempt the DIY route. As far as energy use, ductless mini-splits fall in the middle of the air conditioner spectrum. 

Mini-splits can be linked together to cool more than one room at a time. Finally, the added bonus of a ductless mini-split is that they can also be used to heat rooms during the colder months which makes them a great bargain. Expect to pay between $700 to $2,500 before installation.

Central Air Conditioners

Many newer model homes come with central air conditioning because the entire system is made to both heat and cool an entire house and the air travels behind the walls and through the ductwork. Leave the installation to the pros on this one. Not only do they have the skills, tools, and expertise, but many of them may be able to ‘certify’ your home as energy efficient, which could result in tax breaks and an increase in property values.

Central air conditioners are an investment (about $1,000 to $3,500 not including labor) not only in delivering comfort for you and your family, but adding to your home’s resale value.

person lays on rug looking at laptop in loft style room with window air conditioner
Cavan Images/Cavan via Getty Images

Should I DIY AC Maintenance or Hire a Pro?

Now that you know the basics of how air conditioning works and the units available to you, let’s talk about maintenance.

DIY Air Conditioner Maintenance

Here’s a look at AC maintenance you can do on your own: 

  • Clear debris from the unit 

  • Check and clean condenser coils 

  • Replace HVAC filters

  • Check for loose wires or connections

  • Lubricate motors and bearings

  • Recharge refrigerant

  • Flush your AC drain line to push out clogs

Professional AC Maintenance Plan

Don’t want to worry about yearly maintenance for your AC unit? Hire a pro who will handle it for you. 

Here’s a look at what a professional air conditioning maintenance plan might look like:

  • Air filter replacement

  • Inspect and clean coils

  • Check condensate pump

  • Clean condensate pump if needed 

  • Inspect thermostat 

  • Clear debris from AC unit and clean as needed 

  • Monitor temperature to ensure proper cooling

Should I Repair or Replace My Air Conditioner?

Whether you need to repair or replace your air conditioner depends on a few factors. Most air conditioning units, regardless of the model, should last between 10 and 20 years with regular maintenance. However, if your unit is not cooling to its fullest potential or is making unsettling noises, this will help you decide what steps to take. 

How to Know When It’s Time to Repair Your Air Conditioner

If you haven’t kept up on air conditioner maintenance or your unit is making a funny noise, it might be time for a repair. 

If you hear knocking, rattling, or anything that isn’t the sweet sound of air cooling your space, you might want to do a little investigating. Condenser coils that are located in the outdoor portion of your unit along with the compressor can be replaced if they are cracked or appear damaged. Evaporator coils, which are located in the indoor unit, can also be replaced. You may need to simply brush dirt away on the coils.

How to Know When It’s Time to Replace Your Air Conditioner

If your unit is over 20 years old, not working efficiently, or you see a steady hike in your utility bills, it may be time to replace it.

The good news is that there are national programs that will offer steep discounts on the purchase of a new air conditioning unit. Look for the ‘Energy Star’ logo and sign up for a certification that can qualify you for utility credits as well as tax credits.

Air Conditioner Install Basics

AC units are measured in tons, which refers to the amount of heat they can remove from a home in one hour. The larger your house, the more cooling power you need; however, more than just square footage goes into this calculation. A good AC service professional will take into account room heights and other variables that determine the most appropriate size for your house.

When you hire someone to install a new system, consider these four areas:

  • Sizing: A professional can calculate the home’s cooling load and choose the most appropriate size for your air conditioner.

  • Ductwork: Leaky ducts will waste energy and result in a less-cool home. Installers should use mastic sealant or metal-backed duct tape to make the ductwork airtight.

  • Airflow: Each system has an appropriate airflow rate determined by the manufacturer. If the air moves through the system too fast or too slow, it will be less effective.

  • Refrigerant:  Installers will consult manufacturer requirements to determine the ideal amount of refrigerant necessary. If it’s not properly charged, you lose cooling capacity and end up with higher energy costs. Learn your AC basics to reduce costly AC bills this summer.

You can also retrofit central air conditioning into a house that currently lacks it. 

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