For those of us who needs a little more help with the air conditioners jargon – Laponica has compiled a list and explanation of some of the most common terms. Some terms get a little technical, so we will discuss those in greater detail at a later time. For now we have tried to make things as simple as possible.

In this article we will be covering the terms: air handler, furnace, coil, compressor, condenser, evaporator, expansion valve, refrigerant, and SEER ratings.

Excited? You should be…

Air Handler / Furnace

When you have electric heat it is called an air handler. When you have a gas heater it’s called a furnace. Up north you may have an oil burner, but that is also called a furnace. What they all have in common is a fan that circulates air in the house.


A coil is a heat exchanger. Think of it as the radiator in your car. The radiator is also a coil only with a different name because it’s in your car 🙂


The compressor is a pump. Think of the air compressor you use to fill air in your tires or a high pressure washer. An HVAC compressor is made to pump freon. It may perhaps have a few more fancy attachments to it, but it’s still a pump. When you pump liquids it’s called a pump and when you pump gasses it’s called a compressor.


The condenser is where the compressor sits in the outside unit. Later on we will discuss in more detail what a condenser does besides house the compressor. It gets a little more technical.


Your evaporator sits inside with either an air handler or a furnace. This piece will also be discussed in more detail at later time.

Expansion valve

The expansion valve is a metering device. The compressor pumps freon to the expansion valve under high pressure. In the expansion valve pressure is released causing the temperature in the freon to drop several degrees.


Refrigerant is simply a chemical used in cooling systems for mechanical devices such as the air conditioner in your home or car, refrigerators, or walk-in cooler and freezers. Simply said: the stuff you put in your a/c to make it cold. The first types of air conditioners used toxic and flammable gases, such as ammonia, methyl chloride, or propane. Most have understandably been taken off the market due to their health and environmental risks, but some are making a come back such as ammonia. Larger refrigeration systems such as ones used in warehouses may use ammonia.

The portion of the Clean Air Act that applies to the Heating, Ventilating and Air Conditioning (HVAC) industry encourages the development of ozone-friendly substitutes for chemicals that contain ozone destroying chlorine, which are called hydrochlorofluorocarbons (HCFCs). The chemical refrigerant of choice for more than four decades, referred to as R-22, is in the HCFC category. R-22 is widely used in heat pumps and AC condensing units to heat and cool homes. Today, a refrigerant called R-410A is used because of its ozone-friendly properties.

SEER rating (more detail)

SEER stands for Seasonal Energy Efficiency Rating and is basically a number describing where an a/c unit falls on the efficiency scale – how much energy an air conditioner unit requires to cool your home. The easiest way to think of this is comparing it to how many miles per gallon a specific car is capable of handling. You might consider buying a Prius instead of a Hummer if gas prices is an issue. The same goes for a/c units – you would buy a unit with a higher SEER rating if you want a lower energy bill.

Concerning residential air conditioners, as of January 26th 2006, new units produces today by law must have a SEER rating equal to or greater than 13. Homeowners are not required to upgrade to a higher efficiency model, but with an average lifespan of about 15 to 20 years low efficiency units (depending on ones definition) will eventually go away completely.