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Air Conditioning 101

How do you decide on the best system for your home? First, understand how a typical HVAC system works and why you need the different components. Then when working with your AC contractor, you will know what questions to ask, and better understand your options.

Air conditioning is typically installed in a split system design where one main unit is contained inside and one outside. Both indoor and outdoor units have copper coils in them which is used for cooling indoor air.

When you have an air conditioner as the outdoor unit, the indoor unit is typically a furnace with an evaporator coil. The furnace has the fan motor built in, and this fan is used to force air through the home (even in the summer). The evaporator coil contains the refrigerant. When using a heat pump, the indoor unit might be a furnace (hybrid system), but typically is a fan coil which contains both the fan motor and the indoor coil.

Hover over the diagram below to see definitions of the different components of an HVAC system. Below the diagram you can read in detail about the cooling process:

The points below guide you through the general concepts of how air conditioning works in a system that has indoor air quality components installed. This could differ slightly based on configuration.
  1. Refrigerant is cooled.The outdoor unit (air conditioner or heat pump), compresses refrigerant and sends the chilled refrigerant back inside to the indoor coil. The efficiency of an air conditioner or heat pump (cooling) is measured in a SEER rating.

  2. Fan pulls air from the home.The fan in your furnace or fan coil pulls air from the home through the return air duct.

  3. The air is filtered. Above you can see an air cleaner positioned between the return air ducts and the furnace or fan coil. Such air cleaners can have very high MERV ratings (used to rate the effectiveness of air cleaners), with the ability to filter microscopic particles and viruses out of the air.

  4. The air is cooled.The air is then pushed through the coil system by the variable speed fan motor. The cold refrigerant in the coils absorbs heat and causes moisture to condense, thus cooling and dehumidifying the air. This conditioned air is pushed on by the fan while the heated refrigerant is sent back outside to the air conditioner (condensing unit). The refrigerant is pressurized in the condensing unit which removes the heat. Then the cycle repeats.

  5. Mold is killed & coil efficiency kept high.In the damp interior of an indoor coil system, mold will grow which affects not only the health of your family (mold spores in the air), but the efficiency of your HVAC system. In the system example above, a UV lamp is mounted within the coils to prevent this.

  6. Cooled air sent back into the home.After leaving the indoor coils, cool, dehumidified air is pushed back into the home. In extremely humid climates, a separate whole home dehumidifier can be installed to further remove humidity from the conditioned air.

  7. Air is exchanged. At the top left of the above system layout sits a ventilator. Ventilators are part of complete indoor air quality solutions as they exchange fresh outdoor air for stale indoor air. A ventilator is able to do this with minimal loss of energy, retaining the cooled and dehumidifed air your HVAC system worked hard to produce!

Seasonal Tips


  • Follow manufacturer's routine maintenance directions.
  • Have entire system checked once a year by a qualified service technician.

What Homeowners Can Do:

Check Filters
  • Permanent - Clean with mild detergent, per manufacturer's recommendations, every 30 to 60 days.
  • Replaceable - Replace every 30 to 60 days.

Windows and Doors
  • Keep closed when system is running.
  • Caulk and weatherstrip to close air gaps.
  • Close drapes and shades over windows facing sun.

  • During cooling season, don't wash/dry clothes during warmest times of day (late morning and afternoon).
  • When cooking, use exhaust fan only as needed.
  • Keep thermostat at desired setting.

If you have further questions about HVAC products for your home, simply user our dealer locator: Air Conditioning Contractor