Air Conditioners 101: Complete Guide

| Last Updated: July 27, 2021

Air conditioners are a modern convenience we can’t imagine living without although most of us know little about what they are or how they work. 

Well, you’ve found the right place. We’re going to discuss some of the most pressing topics surrounding air conditioners including how to choose and size one, what kinds are out there, and how to care for one. 

If you want to know a bit more about these amazing machines, feel free to browse through or use our table of contents to go right to what’s weighing on your mind right now.

Table of Contents

Air Conditioner Basics

Air Conditioner Maintenance Tips

Read Before Buying

When To Replace Your Air Conditioner

Popular Air Conditioner Brands


Air Conditioner Basics

What is an Air Conditioner? 

Air conditioners are a modern convenience that makes the hottest temperatures bearable by cooling the air around us. But how do they do that? 

An air conditioner removes hot air from indoors and releases it outdoors while controlling the amount of relative humidity in a room or building, which makes the area feel instantly cooler.

It then cools the air with the help of a refrigerant and releases it back into the building. This provides a comfortable space to enjoy even when outdoor temperatures soar. 

Parts of an Air Conditioner

All air conditioners share some common components. These parts work together to give us the cool air we desire. We will discuss the function of each of these in the section below.

● Compressor

● Refrigerant

● Fan

● Evaporator Coil

● Condenser Coil

How Does an Air Conditioner Work?

We know how great they are, but how do they actually work? Here is a short description of how an air conditioner works.

An air conditioner begins by drawing in air and sending it over refrigerant-filled evaporator coils.

The refrigerant absorbs the heat and changes from a liquid state to a gaseous one before being sent on to the compressor. 

Once it reaches the compressor, the gas is squeezed under high pressure where its volume is decreased. 

Air conditioners are a modern convenience that makes the hottest temperatures bearable by cooling the air around us. We may not understand how the process works, we’re just glad it does.

Types of Air Conditioners

Air conditioners fall under two main types. These are stand-alone and split units. 

Split units have two separate parts and include:

Central Units- Central units are what most people are familiar with. A large unit sits outside and connects to your furnace and ductwork to pump cooled air into your home. 

Ductless Heat Pump/Mini Split- A mini split unit is attached to the wall inside your home along with an outdoor unit that vents the air outside. The unit pumps cooled air directly into the room via the indoor portion without using your ductwork. These are also used for heating. 

Geothermal- Geothermal heating and cooling are a newer form of climate control. They actually work much like a heat pump except they use more natural means to heat and cool. The unit moves temperature controlled fluid through pipes which run beneath your home. In the summer, this fluid absorbs heat from inside and releases it into the ground. In the winter, it can also absorb heat from the ground to warm your home. 

Stand-alone units are all-in-one devices:

The air intake and vent all are part of the same unit. All you do is plug the device in and the unit goes to work. Generally, they still have to be vented outside, but don’t have a separate unit to accomplish this. However, there are windowless units available. These include:

Portable Air Conditioners- These freestanding units often have wheels and can be moved from room to room. Portable air conditioners typically sit on the floor and must be vented outdoors via a hose.

Window Air Conditioners – Window air conditioners sit in a window., usually on a window sill. Gravity keeps the unit in place and the motor portion sits outside the window to allow venting and expulsion of heated air. The front blows cooled air through the vent to the indoor area. 

Evaporative Coolers- This is often called a swamp cooler and uses water to produce cooler air which it then pushes into your home. This type does not remove hot air and is generally less effective than a traditional air conditioner. However, it adds moisture to the air and is particularly beneficial in very dry, desert climates. 

If you want to know more about AC types, check out our article on Types of Air Conditioners

What To Know Before Buying an Air Conditioner

There are many considerations when looking to cool your home. With so many options available, how do you decide which one to spend your hard-earned money on? Let us give you a bit of information to help you out.

What Size Air Conditioner Do I Need?

The size of your air conditioner is vital to achieving the right level of comfort. First, you need to know how large of a space you wish to cool. Are you looking to cool your entire house or just a single room? This will help you decide on the number of BTUs you need.

You may be asking, what is BTU? British Thermal Units (or BTUs) refer to the amount of heat an AC can remove from a room. It is necessary to balance the size of your space with the number of BTUs. Higher BTUs do not always equate to better cooling.

Need more information on sizing an AC

How to Choose an Air Conditioner

Many factors come into play when choosing an air conditioner. Below are a few things to start with.


First, you should determine how much space you intend to cool. Measure your space to ensure you get a model that will meet your cooling demands.


Then, decide whether you need a stand-alone model or a split unit. The unit type you choose will tell you how difficult installation will be and whether you will need a professional to come out.

Energy Efficiency

This is a big decision because the unit you choose will affect your electric bill for years down the road. So don’t take this lightly. If you are on a budget, choose a good, middle-of-the-road option so you get the best of both worlds. There are many ratings that can tell you how efficient an AC is, like SEER, EER, and Energy Star.


Do some research to see a range of prices for a unit that fits your needs. Decide on a budget and do your best to stick to it. Be sure you take into account installation costs and additional supplies needed for installation.

These three main considerations will narrow things down considerably. Also be sure to keep in mind where you plan to install your new AC, what features you truly need, and the size of both your installation space and the unit before purchasing.

To learn more about choosing an AC, feel free to browse our other articles on choosing an air conditioner. and ratings.  

Brand name can be the make-it or break-it point in air conditioners. A good reputation can often put you over the top for one product or another. Some brands have built a loyal following with people who swear by their products and have the track record to back it up. 

Top AC Brands

Here are some of the top brands people love.

Top Central Air Brands

Here are some of the most trusted brands for central air conditioning. You can’t go wrong with one of these companies. Click on a company name to go to the full brand review.






American Standard

Other AC Brand Reviews

Top Stand-Alone Air Conditioner Brands

Here are some of the top brands available for stand-alone air conditioners. Always do research on the model you are looking at to ensure it will meet your needs.


● Frigidaire


● Vornado



● GE

Air Conditioner Maintenance Tips

An air conditioner is an investment that you hope will last for many years. In order for that to happen, you will need to handle some regular maintenance as well as deal with some issues here and there. You can find an HVAC maintenance list here. 

Common AC Issues

Many issues can come up when using an air conditioner. Here are some of the most common ones.

AC Not Turning On

Few things are as frustrating as a sweltering day when your AC won’t turn on. The first thing to do is try turning off the breaker box and resetting the power. After that, check your thermostat to make sure it is on and set to a cooler temperature than the room’s ambient temperature. Pull out the filter and take a look, is it dirty, clogged, facing the right direction? Finally, check for a reset button, if included on your unit.

AC Is Leaking

There are several things to consider if you notice a leak from your air conditioner. First check the filter. A clogged filter can cause many problems. The next thing to look at is your condensate drain line. Is it clogged or damaged? Clean or replace as necessary. Also, be sure to check your refrigerant level. If the leak is refrigerant, it will need to be serviced by a professional.

Air Conditioner is Making Noise

If your AC suddenly starts making noise, it can be alarming. A possible culprit is something stuck in your outdoor unit. Look for branches or leaves and carefully remove them. If that is not the case, check and clean the fan blades and replace the filter. Both of these things can make an AC work harder than normal, causing undesirable noise.

Coils Are Frozen or Corroded

If your coils are covered in ice or are corroded, start by defrosting and cleaning them. Again, check the filter. A clogged filter can cause too much strain on your unit and freeze the coils. Make sure your condensate drain is clear and also check your thermostat and fans to ensure they are operating properly.

Air Conditioner Troubleshooting

If something on your AC is not working correctly, it can be frustrating. Here are a few general steps when your unit encounters trouble.

Power Check

Check the electrical outlet to be sure it is operational and your unit is plugged in. Find your circuit breaker and check to see if the breaker is tripped. If so, turn it off and back on to reset the circuit.

Change the Filter

This may sound like a broken record, but really, nearly any issue can stem from a dirty filter. It is a simple, yet often overlooked troubleshooting tip that can solve many problems. Besides, the cleaner the filter, the cleaner the air in your home.

Inspect All Parts of the Unit

Are the coils frozen? Is the condenser blocked or dirty? Is the fan running? These can point you in the right direction to figure out where the problem is originating. Also, check your thermostat to make sure it is working.

Looking for more troubleshooting tips? Check out our Air Conditioner Repair Guide.

How to Install an Air Conditioner

Installing an air conditioner can be a challenging task. It may even be against regulations in some areas, particularly in developments with a homeowner’s association. If you get a window unit or a portable AC, these can easily be installed by any do-it-yourselfer. However, a central air unit requires much more expertise and is better handled by a professional.

To install a window AC unit, you will need to:

1. Remove or pull back all window coverings

2. Attach the side panels

3. Insert and secure window air conditioner using L-brackets

4. Extend side panels to the edge of the window and lock into place

5. Lower the window into place and gently secure it on top of the air conditioner

6. Use a window lock to ensure your window cannot be opened

Here are the steps to install a portable air conditioner:

1. Read your user manual and installation instructions

2. Choose a location close to a window for venting- if no window is available, you can opt to vent out a sliding glass door, through a wall, or out the attic

3. Get a window kit and measure your window

4. Make the necessary cuts and adjustments to the window kit

5. Install the window kit

6. Attach the hose and fit into the opening

7. Secure the adapter and hose to fill the surrounding gaps

If you’ve decided to tackle the big task of installing a central air conditioner, here are the basic steps you’ll need:

1. Read your user manual- all info contained in there takes precedence

2. Ensure proper ductwork is installed and/or is clean and ready

3. Install the outdoor condenser on top of a condenser pad

4. Cut a hole in the wall large enough to accommodate wires and lines to connect to your furnace

5. Install the evaporator coil in your furnace

6. Connect the indoor and outdoor units

7. Connect the thermostat to the unit

8. Connect the wires to provide power to the unit

9. Test out your new AC

How to Clean an Air Conditioner

All AC parts should be cleaned regularly. Here are some tips on cleaning.

To Clean the Indoor Portion

To clean the inside unit of your air conditioner, you first need to turn off the power to reduce any risk.

Open the unit. You may need to remove foil tape, screws, and/or bolts to access the inside.

Remove the filter and inspect. If it has been more than a month or two, or if the filter is visibly dirty, replace it or wash (if washable)

Vacuum out any dust or dirt that has accumulated inside.

Use compressed air to blow off the evaporator coils. If still dirty, you can use a soft brush and coil cleaner to clean the coils. Vacuum or wipe out loosened dirt.

Replace the door and bolt, screw, or tape it back into place.

To Clean the Outdoor Portion

Ensure the power is off. Remove the outer door of the AC.

Scoop or wipe out any dirt and debris that has accumulated inside. Grass, dirt, dust, leaves, and branches are common.

Use a commercial coil cleaner to clean the coils. These contain potentially harmful substances so use gloves and do not get the cleaner on your skin.

Spray the cleaner on, let sit per directions, then use a water hose to rinse them. Do not use a pressure washer, as this can damage the fins of the unit.

Use a fin comb to straighten the fins to allow proper airflow.

Once everything is back to looking like new, allow the unit to dry, replace the outer door, and you are ready to go.

Be cautious with the chemicals in cleaners, here is more information on Air Conditioner Chemical Wash and Coil Cleaners, and How to Clean Air Conditioner Coils.

How Often Should I Clean an Air Conditioner?

Filters should be changed every 1-3 months depending on your usage. The coils and outdoor unit should be cleaned at least twice per year. Cleaning in the spring before the hot weather hits and again in the winter before covering the unit are the most common.

The indoor unit should be serviced and the blower and blower motor cleaned regularly. This is best done by a professional.

Stand-alone units should also be taken apart and cleaned at least twice per year. Filters should be cleaned or changed at least monthly during high usage. 

For a detailed guide to cleaning your AC, check out How To Clean An Air Conditioner.  

When is it Time to Replace My Air Conditioner?

Air conditioners generally last 10-15 years. The older they are, the less efficient they likely are, too.

As your unit ages, it gives off some signs that it is time to replace.

1. Your Unit Keeps Breaking Down

If your AC seems like a money pit that you feed into multiple times each year just to get a bit of cool air, it is probably time to replace.

2. Your Energy Bills Are Too High

If your bill goes through the roof every summer, your air conditioner is likely working harder than it should and should be replaced. 

3. Your House Doesn’t Feel As Cool As It Used To

If the temperature in your house is not as comfortable as it was in the past, it may be that your air conditioner isn’t functioning properly and needs to be replaced.

4. Your House Gets Bigger or You Add More People

The size of your house and number of people can greatly affect the ability of your AC to keep up. If you have recently added several people to your household or added a room or two and notice your house is a little too warm no matter how low you turn the thermostat, you may need a higher-powered unit.

5. Your AC is Just Old

If your unit is over 10 years old and you are having trouble getting it to cool your house to your liking, it may be time to bite the bullet and replace before it goes out completely. 

6. You Live Where It’s Hot Most of the Time

If the area where you live is hot more often than not, you probably use your unit more than people in varying climates, putting more demand on your unit year-round. This can cause issues to come up well before the ten-year mark, which require you to replace sooner.

Can You Really Find a Quality Air Conditioner That’s Affordable? 

Air conditioners range from under $100 to several thousand dollars. With such a range, you can find something that will hit the nail on the head. 

High-end units require deep pockets but will be more efficient, have more features, and may last longer. However, if you are willing to sacrifice some of those extras, you can bring your cost down significantly. 

If you can’t shell out money for a large central unit, consider getting a few window or portable units to put in your most frequented rooms while employing other methods to keep your house cool.

A trade-off might be having a slightly higher monthly electric bill to save hundreds or even thousands of dollars on an AC.  

Here is some more helpful information when considering an AC replacement:

AC Replacement Cost
Installation vs Maintenance
How Long Do AC Units Last?
Best Time To Buy an Air Conditioner


Air conditioners are something most people wouldn’t want to live without. They definitely make those blistering days tolerable.

We tried to cover as many aspects as possible but if you still have questions or need more details or information on a topic, browse through our many air conditioner articles and reviews. We’re sure you’ll find what you’re looking for.

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My name is Bob Wells and I am a retired HVAC tech from Washington state. I am currently retired and no longer do much with HVAC, however, I feel like I have a lot of knowledge in the subject and I wanted to create a website where I could talk about what I've learned and help upcoming HVAC techs. Find more info about me and HVAC Training 101.