In 1902 electrical engineer Willis Haviland Carrier developed the 1st modern air conditioning system . The Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, N.Y. was having a problem with humidity in their building. Because of the humidity, the paper stock at the plant would sometimes absorb moisture from the warm summer air. This made it difficult to apply the layered inking techniques of the time. Carrier treated the air inside the building by blowing it across chilled pipes. The air cooled as it passed across the cold pipes, and since cool air cannot carry as much moisture as warm air, the process reduced the humidity in the plant and stabilized the moisture content of the paper. Reducing the humidity also had the side benefit of lowering the air temperature — and a new technology was born.

Carrier realized he’d developed something with far-reaching potential, and it wasn’t long before air-conditioning systems started popping up in theaters and stores, making the long, hot summer months much more comfortable [source: Time].

There are 2 basic types of air conditioners—room air conditioners and central air conditioners. All air conditioners, whether they’re small window units or central systems that cool an entire house, work on a similar cooling principle – They control air temperature, humidity, and the quality of the air in your home. An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and the condenser are coils of copper tubing surrounded by aluminum cooling fins.

The typical central air conditioning system has an outdoor air conditioning, or “compressor bearing unit” and an indoor coil, which is usually installed on top of the furnace in the home. The compressor pumps refrigerant through the system to gather heat and moisture from indoors and remove it from the home. Heat and moisture are removed from the home when warm air from inside the home is blown over the cooled indoor coil. The heat in the air transfers to the coil, thereby “cooling” the air. The heat that has transferred to the coil is then “pumped” to the exterior of the home, while the cooled air is pumped back inside, helping to maintain a comfortable indoor temperature.


Lets get a little more technical – Air conditioner systems work by manufacturing cool air through the evaporation of some kind of refrigerant (such as freon). Heat is transferred through the coils from inside the house to the outside, as the refrigerant absorbs the heat and releases it to the outside. The refrigerant changes from liquid to gas during this cycle and as it does so, it absorbs heat.  When it changes back from gas to a liquid state it releases this heat.  The remaining liquid in the indoor coil absorbs heat from the inside air, which turns into a low-temperature gas cooling the indoor air.  Cool air is circulated through a system of supply and return ducts.  These supply ducts and registers carry cooled air through the home.  When the cooled air becomes warmer as it circulates through the home, it flows back to the central air conditioner through return ducts and registers.

Types of Air Conditioners

Room air conditioners – are specialized units designed and sized to cool one room or a large open area. They are installed either in windows or through walls. These portable units do not use ducts to distribute air, instead, they rely on a fan to blow air across and around the room. Small capacity units can be plugged into standard power outlets, while larger units may need to be wired in. 

The main types of conditioning units include- Central air conditionersDuctless split Air Conditioners, Window Air Conditioners, Wall Mounted Air Conditioners and Portable Air Conditioners.

Wall, Window and Portable AC Units

Wall, Window and Portable AC Units

Window Air conditioners sits in your window. They are usually made for double-hung windows, and are generally the cheapest option. These units provide better targeted cooling than central air conditioners. They sit on top of a window frame in a partially opened window, with the warm air exhaust system facing the outside and the cooling system directed to the inside of your room. Some window AC units can alternatively be installed directly through a wall that faces the outside if a window is not available. They can be easily removed and stored when the heat season is over.

These self-contained cooling appliances are often more efficient, less expensive, and available in a wide range of sizes and cooling capacities.

Room Air Conditioner

Window Air Conditioner

Wall Mounted Air Conditioners are a close cousin to the Window AC, the Wall Mounted AC will require you to have a hole cut into your wall. They are an excellent solution for cooling rooms that don’t have a window or when window installation is not desired. These room air conditioners are ideal for cooling single rooms and areas of your home that are typically warm. In addition to providing supplemental cooling to central air systems, some through-wall air conditioners also have heating capabilities. Many models are equipped with a variety of features including programmable timers, digital thermostats, remote controls, and directional airflow. While a hassle to install, they are usually the easiest to remove and repair and range around the same price as the Window air conditioner.

Wall Mounted Air Conditioner

Wall Mounted Air Conditioner

Portable Air Conditioners provides cooling to spaces without access to central AC or areas that simply need supplemental cooling. Portable ACs pull in hot air that needs to be exhausted from the space it’s cooling. For this reason, all portable air conditioners must be vented using a single- or dual-hose exhaust system. Portable air conditioners can be installed through a window, wall, sliding glass door, or even a drop ceiling.

In addition to cooling power, portable air conditioners also help dehumidify. This not only keeps your room cool, but also removes excess moisture that could lead to indoor air quality problems.

Many portable air conditioners include features like remote controls, multiple cooling speeds, programmable timers, and additional operating modes.

Unlike a window air conditioner, all the mechanical parts of a portable air conditioner are sitting in the room you’re trying to cool. This contributes to the noise and less-than-capable cooling, as the portable unit is using conditioned air from the room to cool the condenser and exhausts the hot air out an ungainly exhaust hose that resembles a dryer vent. That creates negative pressure causing unconditioned warm air from surrounding rooms or outdoors to be drawn into the room you’re trying keep cool.

Portable Air Conditioner

Portable Air Conditioner

Ductless split AC systems are multi-component air conditioners that provide effective cooling throughout your home, and without inefficient ductwork. Mini splits come as single- or multi-zone models and are capable of cooling up to 4 areas of your home or office. They install at the top of your wall for space-saving functionality and are perfect for rooms with limited window space, and homes without central ACs.

The ductless mini-split system consists of an indoor air handler and a outdoor condenser. In addition to the standard condenser unit, some mini-split AC models include several air handlers, which allow you to program separate settings for multiple rooms at one time. Many ductless mini-split air conditioner units are shipped with with features such as 24-hour timers, remote controls, reusable air filters, and auto swing louvers.


Ductless AC

Central air conditioners have two separate components (a split system): The condenser and the evaporator. The condensing unit of the air conditioner is located outside the home and the evaporator coil part is located inside in the air handler. The handler generally is located somewhere in the home such as the garage, attic, or a hall closet. The duct system generally runs through the attic, crawl space, or living area of the home to distribute conditioned air to the various rooms.

Most central air conditioners are connected to a home’s forced-air distribution system. Thus, the same motor, blower, and ductwork used for heating are used to distribute cool air from the air conditioning system.

Central Air Conditioner

Central Air Conditioner [source – How Stuff Works]

All climate-control devices or systems have three basic components: a source of warmed or cooled air, a means of distributing the air to the rooms being heated or cooled, and a control used to regulate the system (e.g., thermostat). The sources of warm air, such as a furnace, and cool air, such as an air conditioner, in a house often use the same distribution and control systems. If your house has central air conditioning, cool air probably flows through the same ducts that heat does and is regulated by the same thermostat.

All HVAC units burn fuel. Air conditioners use electricity. The heat pump — an electrically powered climate control unit — both heats and cools air. In summer it extracts heat from the air inside your home. In winter it pulls heat from the air outside and uses this heat to warm the air inside.

When an air conditioner is turned on, electrical power is used to cool a gas in a coil to its liquid state. Warm air in your home is cooled by contact with the cooling coil, and this cooled air is channeled to the rooms of your home through ducts and out registers or — in the case of room air conditioners — directly from the unit itself.