We Now Provide Electrical Services!


We Now Provide Electrical Services!


We Now Provide Electrical Services!


Common Terminology to Help You Better Understand Your AC Unit

Those of us in the HVAC use specialized air conditioning terms when referring to different aspects of your cooling system. While these terms help us give you a detailed description of equipment or repair needs, common air conditioning terms sometimes sound like a foreign language to Indianapolis homeowners who aren’t familiar.

While you don’t need to know all the specialized HVAC terms, a knowledge of common air conditioning terms goes a long way towards helping you better understand your cooling system. Our HVAC pros give you a layman’s definition of some of the most common air conditioning terms you are likely to hear when we discuss new equipment, repair needs, or even maintenance!

Take a look at the definitions for common air conditioning terms below before your next appointment. If you have questions about what something means that comes up in conversation with our staff, please ask us about it! We know our terminology isn’t something that every homeowner is familiar with, and we are happy to take the time to explain – it’s our job to make sure you are comfortable and have a good understanding of our products and services!

Common Air Conditioning Terms: Cooling Systems

  • Split system: This is likely the most common type of cooling system in Indianapolis area homes. They consist of an indoor unit and an outdoor unit, hence the “split.” Inside is the evaporator coil and air handling components, and outside is the condenser and compressor. This is a central cooling system that sends cooled air through the ducts into the home.

  • Air conditioner: The term “air conditioner” is commonly used to describe any system that cools air, but for our purposes, we discuss an air conditioner that is part of a typical split central air conditioning system. Air conditioners move heat from inside the home to the air outside to lower temperatures indoors. In a split system, there is an outdoor unit (often called a condensing unit) and an indoor unit – many air conditioners use the furnace components for blower motors instead of an air handler.

  • Heat pump: A heat pump is the outdoor unit that transfers heat from the air in the home to the  (or to a ground or water source for geothermal heat pump systems) to create cooler temperatures indoors. It differs from an air conditioner because it is also able to provide heating. Heat pumps are paired with an air handler inside the home.

  • Packaged air conditioner: Packaged air conditioners contain all elements of a cooling system in one cabinet. They may also contain heating components. Packaged unit air conditioners are available for residential use, though are more common in commercial applications. They are typically installed on a concrete pad outside the structure, or on its roof.

  • Ductless mini-split system: Ductless mini-split systems allow for multiple (typically up to 4 or 6, depending on the model) indoor air handling units supported by a single outdoor unit. They do not use ducts – conditioned air is delivered directly into the living area where an air handler is installed.

Common Air Conditioning Terms: Equipment Basics

  • Air handler: The air handler is the indoor unit of a split system. It is responsible for circulating conditioned air produced by the cooling system, using a blower motor. Depending on the model, they may also include supplemental electric heating elements and filtration.

  • Evaporator coil: Located indoors, this is the first step in the cooling process. The evaporator coil absorbs heat from indoor air.

  • Condenser coil: The condenser coil completes the cooling process. Located in the outdoor unit, it releases the heat from refrigerant into the outdoor air.

  • Compressor: The compressor raises the pressure and temperature of refrigerant moving through the cooling system as part of the cooling process.

  • Condensate pan: Also called a drip pan, it collects moisture that forms during the cooling process. Connected is the condensate drain line, which allows this water to flow away from the unit and out of the home.

  • Ducts: Ducts carry air from the air conditioner to the living spaces. They are typically made from sheet metal or flexible tubing. The conditioned air from the cooling system runs to living areas through the supply ducts, and air returns back to the cooling system through the return ducts.

  • Expansion valve: The expansion valve depressurizes and cools refrigerant so it can enter the evaporator coil and allows it to convert from liquid to gas. The expansion valve also controls refrigerant and voltage flow into the evaporator.

  • Filter: The filter captures airborne contaminants before air reaches the indoor cooling system components. Its main purpose is to protect system components from these contaminants, but by doing so, the filter also improves indoor air quality.

  • Line set: The line set is made up of two refrigerant lines that connect the indoor evaporator coil to the outdoor condensing unit. The smaller uninsulated copper line transports liquid refrigerant while the larger insulated line is for suction.

  • Plenum: The plenum connects the air handler or furnace to the return ductwork of the home.

  • Refrigerant: Refrigerant carries heat between cooling system components. Older cooling systems may use Freon, or R-22, which is being phased out in favor of Puron, or R-410a, which is environmentally friendly.

  • Reversing valve: The component with a heat pump system that makes the switch between heating and cooling modes.

Common Air Conditioning Terms: Efficiency and Operation

  • BTU: British thermal unit, a heat equivalent measure that shows how much energy is needed to raise a pound of water one degree Fahrenheit. This measure is used to express an air conditioner’s ability to remove heat.

  • BTU/H: British thermal units per hour shows the number of BTUs an air conditioner is able to extract from a space in an hour.

  • Capacity: An air conditioner’s ability to remove heat from a space.

  • EER: Energy Efficiency Ratio (EER) measures a geothermal heat pump or window air conditioner’s cooling efficiency. It is calculated by Btu/hr of cooling divided by energy input in watts.

  • MERV: Minimum Efficiency Reporting Value (MERV) measures the efficacy of a filter. MERV ranges from 1 to 16, with one being the lowest and 16 being the highest.

  • SEER: Seasonal Energy Efficiency Ratio (SEER) rates the efficiency of an air conditioner, measuring the cooling output over a normal season, divided by the total energy input to the unit over the same period of time. In Indiana, the minimum SEER for new units is 13. The higher the SEER, the more efficient the unit.

Common Air Conditioning Terms: Other Phrases and Terms

  • Air balance: This describes an HVAC system’s air distribution – balanced systems deliver enough air to match the amounts that all system components require at any time.

  • Air changes per hour: The number of times a home’s entire volume of indoor air is replaced through air conditioning or natural ventilation over the course of an hour.

  • Air exchange rate: How fast indoor air is replaced by conditioned or outdoor air.

  • Air flow volume: How much air is circulated by your air conditioner within your home – usually measured in cubic feet per minute.

  • Air infiltration: The unwanted entrance of air into an area, caused by leakage, wind, or temperature differentials.

  • Ambient air: Unconditioned air.

  • Charge: The amount of refrigerant within the air conditioner. This is checked using gauges to measure refrigerant pressure.

  • Cooling load: The rate that sensible and latent heat need to be removed from an area to maintain desired temperatures. Cooling load is calculated using Manual J.

  • Cycling: The air conditioner’s cycle of starting up, processing an amount of air, and then turning off.

  • Dry charged unit: An air conditioner that is installed without refrigerant, and is charged after installation.

  • Latent heat: The amount of heat that needs to be removed from the air to decrease moisture in a space.

  • Refrigerant charge: The process of adding refrigerant to the air conditioning system’s closed refrigerant system. This may be performed after the installation of a dry-charged air conditioner or once repairs to refrigerant lines are made.

  • Sensible heat: The amount of heat that needs to be removed from the air to decrease temperature in a space.

  • Static pressure: Pressure within the duct system. If it is too high, proper airflow is hindered.

  • Tons of cooling: The capacity of an air conditioner. One ton of cooling equals 12,000 BTU/H.

  • Two-stage cooling: An air conditioner that operates at two levels using a variable speed motor, an energy saving level, and a higher energy level when outdoor conditions warrant.

  • Zoning: Zoning divides a home into different zones and allows the air conditioning to be independently controlled in each zone. This is done to improve comfort indoors and to enhance HVAC system efficiency.

Talk Air Conditioning Terms with Williams Comfort Air!

Is it time for a conversation about your cooling system? Whether you need a new air conditioner, air conditioner repair, or seasonal maintenance, Williams Comfort Air is here to help you with all your cooling system needs! Let our NATE-certified technicians assess your needs – we take the time to decode complicated air conditioning terms so you have a clear understanding of the equipment or repairs you need, and what we are doing.

Let’s talk air conditioning terms and determine what your Indianapolis home needs to stay cool – contact us today!

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