Air Conditioning & Heating Terms | San Antonio, Helpful Definitions

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AC & Heating Terms

Wilks Air Conditioning & Heating has defined some AC & Heating Terms to help you better understand your air conditioning and heating systems.

Central Air Conditioning

A system is made up of four main components including an air handler, an evaporator coil, a condensing coil, and air ducts which deliver the air to individual rooms throughout your home. All of the components of your air conditioning system need to be carefully matched together during the original installation. A mismatched system will operate poorly, and in some cases will not operate at all.

Air Handler (typically the furnace blower is used)

Blows air through the evaporator coil and into the duct work to be circulated throughout the home. An air filter should always be located on the intake side of the furnace to clean the air before it is cooled and circulated throughout the home.

When the furnace is used for air conditioning its blower will be energized in high speed, which makes more noise and moves more air than when it operates in the heating mode.

Evaporator Coil

Sitting on top of the furnace and enclosed in an insulated sheet-metal box, the evaporator coil is connected to the outside condenser by two copper tubes, one of which is insulated with a thick rubber coating. Refrigerant (R-22 or R-410a) will circulate through this coil to cause the cooling effect.


The outdoor unit of a split system is the condenser. It consists of the compressor, which is a pump that circulates the refrigerant through the evaporator coil, a large radiator coil to transfer heat, and a fan to blow air through the coil to keep it cool. It is important to keep the area around the condenser clear so it can operate properly.

Air Ducts

Today’s duct work consists of insulated flexible tubes that snake across the attic floor or under the house. Unfortunately, cooling ducts are out of sight and therefore out of mind and tend to be neglected when it comes to cleaning and repair. A recent study concluded that the average home loses up to 30% of the cool air before it ever gets to the rooms where it’s needed due to leaking duct work. Combined with poorly designed supply registers that don’t allow for good air circulation, you could be spending up to 50% more on your cooling cost than you would with a well-designed, sealed duct system, and adjustable supply vents.


Humidity refers to the moisture that has evaporated into the air and exists as an invisible gas. As the heat is removed from the air passing over the evaporator, moisture condenses out of it. We know this moisture as condensation and provide a drain line for its disposal. When the humidity is high, there is more moisture in the air and more condensate will be formed. If your home construction doesn’t allow for a regular gravity flow drain to dispose of the condensate, a small water pump may be used that will pump the water to a convenient drain or outside to a small, dry well dug next to your condensing unit and filled with gravel. This condensate pump contains a float switch and will cycle on and off as needed.

Size Matters

Your system needs to be properly sized for your home. The size of your central air conditioner is measured in tons of refrigeration. One ton is equal to 12,000 BTU’s/hour of cooling capacity. A three-ton system, for instance, would have 36,000 BTU’s of cooling capacity. Too small a system will not cool your home adequately on hot days. And too large a system will cool the air in your home so fast that the humidity is not removed, leaving you with a sometimes cold, clammy feeling and, in severe instances, humidity condensing into water and dripping off of your air registers. Your comfort consultant will perform a heat gain analysis on your home to help you decide on the system that will best meet your needs.


SEER stands for “Seasonal Energy Efficiency Ratio” and it is a number by which you can compare the efficiency ratings of different air conditioners. The minimum rating allowed today is 13 SEER and so every equipment manufacturer had to produce a 13 SEER unit. Don’t be fooled into thinking that all 13 SEER units are the same. The differences become apparent when you look closer at things like construction, quality reliability, durability, and enhanced warranties.