Air Conditioning Units: Then & Now

summer is coming, lets throw on our best dresses and stand by the air conditioningAir conditioning is a luxury many of us take for granted these days, as it is a standard piece of equipment in most U.S. homes now. It has impacted our lives in many ways that we don’t necessarily think about, because most of us are fortunate enough to live in a home with an air conditioning unit. Cooling technology has advanced greatly to improve our comfort and health; let’s take a look at air conditioning, then and now!

Before residential air conditioning, homes were hot. In the heat of the summer, homes were not the comfortable, cool sanctuary they are today. Families slept outside to catch a cool breeze because closed-up homes were too hot. Windows were opened as much as possible to provide some ventilation to the household. Sweating was inevitable, along with body odor. (yuck!)


  1. It started with Hand Fans

    People were limited in ways to keep cool. Hand fans were popular throughout history. In the early 1900s, electric fans first appeared in U.S. homes.

  2. The air conditioner was finally invented in 1902

    The modern air conditioning unit was invented by Willis Carrier in 1902, and textile mill engineer Stuart Cramer was the first to coin the term “air conditioning” in 1906. Air conditioning was first installed residentially in 1914; the unit was 7 feet high, 6 feet wide, and 20 feet long! Obviously, the size of the system were quite costly and only could be installed where space was ample; wealthy people with large homes were really the only ones who could access it. Early air conditioners cost anywhere from $10,000 to $50,000 in their time — $120,000 to $600,000 in today’s dollars!

  3. The first room air conditioner unit was invented in 1931

    In 1931, H.H. Schultz and J.Q. Sherman invented the first room air conditioner. The unit sat on the ledge of a window, just as modern room air conditioners often do. Even so, these systems were still very expensive. For example, the 1938 Chrysler air conditioner cost $416; the average hourly wage was $0.64, so it took 650 hours of work to be able to afford this purchase.

  4. It wasn’t until 1970 that AC units made it into most American homes

    Post WWII, air conditioning became something of a status symbol. Window air conditioner units were a hot commodity, with over one million units sold in 1953. In the 1970s, central air conditioning systems made their way into homes, using Freon-12 (also known as R-12) as coolant.

  5. Different specs:

    Residential air conditioning has come such a long way in the past 100 years. Early air conditioner units were loud, lacked efficiency, and were expensive to operate. Today’s air conditioning manufacturers have taken great strides to develop cooling technology that is efficient and convenient, providing consumers with seemingly endless equipment choices. Air conditioning has also become more environmentally friendly as research has shown that Freon is linked to ozone depletion; currently, R-22 refrigerant is being phased out and environmentally-friendly R401A refrigerant is the new standard.

  6. Price differences:

    Air conditioning units have become much more affordable over the years, leading to their widespread use in American homes. Today, more than 80 percent of homes in the United States have an air conditioning unit. The addition of the air conditioner has changed architecture, making it possible to have windowless buildings and dwellings without patios.

  7. Fact: Air conditioners save lives

    Air conditioning didn’t just change the nation’s comfort — it has also played a significant role in lowering the number of heat-related deaths. Between 1960 and 2004, the number of heat-related deaths in the United States was a staggering 80 percent less than between 1900 and 1959. Air conditioning saves lives, providing respite from dangerous outdoor temperatures.

Understanding Your Air Conditioning Unit: It Doesn’t Have to be Scary!

Now that many of us are fortunate enough to have air conditioner units, it’s important to understand how they work! Have you ever looked at your system and wondered what all of the numbers and letters mean? If you have, you’re not alone! Unless you’re a trained professional, you will likely not understand a lot of the labeling on your system. We will go over a few common items on your heating and air conditioning unit’s nameplate so that you can better understand what you’re seeing when you read it.

understanding your hvac system picture 1

To begin, we have the model number. This is usually printed on a label on the system, which is often located on the inside of the access panel or it will be on the inside or outside wall of the unit. Frequently, this will also be where the serial number will be located. The model number usually indicates the heating or cooling capacity, but on newer systems the cooling capacity can also be stated separately.

The model number will indicate the tonnage of the air conditioning or heat pump system. Tonnage is a unit of measure that is used to describe the cooling or heating capacity of a system. A ton of cooling is based upon how much heat is needed to melt one ton (which is 2000 lbs.) of ice in 24 hours. A ton of cooling equals 12,000 BTU/hour. BTU is short for British Thermal Unit. For example, if a system is 30,000 BTU/hour, it is said to be a 2.5 ton system. Within the model number, there will be a number that is divisible by 12. That number will determine allow you to determine the tonnage of the system. If you see the number 30 in the model number, that will tell you that your system is 2.5 tons.

If you have a newer air conditioning unit, the cooling capacity will generally be indicated directly on the nameplate. Usually, the nameplate will be located on a sticker on the outside or inside of the unit

Also frequently listed on the nameplate is the voltage. The voltage indicates how much electricity the system uses. The voltage of a system will remain constant regardless of the load that is placed on it. However, as more of a load is placed on the system, the current will increase. As a result, the amount of watts used will increase. Additionally, you may also see how many phases your system is. For most residential applications, it will be single phase.

Another important piece of information on the nameplate will be the Rated Load Amperage, often times labeled as RLA. This is a calculation that is used to get approval by the Underwriters Laboratories for a compressor motor. You will also see the Full Load Amperage, often labeled as FLA. With an increase in load on a motor, the total amperage needed to power the motor increases. When the full load of the motor is reached, the total amperage that the motor is drawing at this point is the full load amperage, or FLA. This is a value that is used in order to size field wires and fuses.

understanding your hvac system picture 2Next, the serial number, which is usually located on the nameplate, can tell you some important information as well. While this may look like a long string of numbers and letters that do not mean anything, they sometimes can tell you the age of your system. The serial number of an air conditioning unit means different things on different systems. In general, the serial number will tell you the age of your system. If you are unsure about the serial number for your system, check out our manualspage. This page has many manuals from different brands that can help you learn more about information about your system, including the meaning of your serial number. Knowing the age of your system will go a long way to ensure its proper maintenance.


understanding your hvac system picture 3Another common and important piece of information on your system is its Energy Efficiency Ratio. This information tells you how much electricity you use to obtain a certain amount of cooling. The unit of measure for this is KW per hour of electricity used/1,000 BTU’s. You will usually be able to find this information on an Energy Guide sticker that is bright yellow and often located on the side of the system. This sticker will tell you your estimated yearly operating cost as well.


As you can see, there are many common items on that will be labeled on your air conditioning unit. While it may seem overwhelming, a simple understanding will help you make the best choice in the long-term maintenance of your system. If you have further questions about your system, browse our contractor directory and contact a professional near you!

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