The basic types
of air conditioners are room air conditioners, split-system central air
conditioners and packaged central air conditioners.
Room Air Conditioners
Room air conditioners cool rooms rather than the entire
home. If they provide cooling only where they're needed, room air conditioners
are less expensive to operate than central units, even though their efficiency
is generally lower than that of central air conditioners. Smaller room air
conditioners – those drawing less than 7.5 amps of electricity – can be
plugged into any 15- or 20-amp, 115-volt household circuit that is not shared
with any other major appliances. Larger room air conditioners – those drawing
more than 7.5 amps – need their own dedicated 115-volt circuit. The largest
models require a dedicated 230-volt circuit.
Central Air Conditioners
Central air conditioners circulate cool air
through a system of supply and return ducts. Supply ducts and registers –
openings in the walls, floors, or ceilings covered by grills – carry cooled
air from the air conditioner to the home. This cooled air becomes warmer as it
circulates through the home. Then it flows back to the central air conditioner
through return ducts and registers. A central air conditioner is either a
split-system unit or a packaged unit. In a split-system central air
conditioner, an outdoor
metal cabinet contains the condenser and compressor, and an indoor cabinet
contains the evaporator. In many split-system air conditioners, this indoor
cabinet also contains a furnace or the indoor part of a heat pump. The air
conditioner's evaporator coil is installed in the cabinet or main supply duct
of this furnace or heat pump. If your home already has a furnace but no air
conditioner, a split-system is the most economical central air conditioner to
install. In a packaged central air conditioner, the
evaporator, condenser, and compressor are all located in one cabinet, which
usually is placed on a roof or on a concrete slab next to the house's
foundation. This type of air conditioner also is used in small commercial
buildings. Air supply and return ducts come from indoors through the home's
exterior wall or roof to connect with the packaged air conditioner, which is
usually located outdoors. Packaged air conditioners often include electric
heating coils or a natural gas furnace. This combination of air conditioner
and central heater eliminates the need for a separate furnace indoors.
Maintaining Existing Air Conditioners
Older air conditioners may still be able to
offer years of relatively efficient use. However, making your older air
conditioner last requires you to perform proper operation and maintenance.
Air Conditioning Problems
One of the most common air
conditioning problems is improper operation. If your air conditioner is on, be
sure to close your home's windows and outside doors. Other common problems with
existing air conditioners result from faulty installation, poor service
procedures and inadequate maintenance. Improper installation of your air
conditioner can result in leaky ducts and low air flow. Many times, the
refrigerant charge – the amount of refrigerant in the system – does not match
the manufacturer's specifications. If proper refrigerant charging is not
performed during installation, the performance and efficiency of the unit is
impaired. Service technicians often fail to find refrigerant charging problems
or even worsen existing problems by adding refrigerant to a system that is
already full. Air conditioner manufacturers generally make rugged, high quality
products. If your air conditioner fails, it is usually for one of the common
reasons listed below:
- refrigerant leaks. If your air conditioner is low
on refrigerant, either it was undercharged at installation, or it leaks. If it
leaks, simply adding refrigerant is not a solution. A trained technician
should fix any leak, test the repair and then charge the system with the
correct amount of refrigerant. Remember that the performance and efficiency of
your air conditioner is greatest when the refrigerant charge exactly matches
the manufacturer's specification, and is neither undercharged nor overcharged.
- inadequate maintenance. If you allow filters and
air conditioning coils to become dirty, the air conditioner will not work
properly, and the compressor or fans are likely to fail prematurely.
- electric control failure. The compressor and fan
controls can wear out, especially when the air conditioner turns on and off
frequently, as is common when a system is oversized. Because corrosion of wire
and terminals is also a problem in many systems, electrical connections and
contacts should be checked during a professional service call.
Regular Maintenance An air conditioner's filters, coils and fins
require regular maintenance for the unit to function effectively and efficiently
throughout its years of service. Neglecting necessary maintenance ensures a
steady decline in air conditioning performance while energy use steadily
Air Conditioner Filters.
The most important maintenance task that will ensure the efficiency of your
air conditioner is to routinely replace or clean its filters. Clogged, dirty
filters block normal air flow and reduce a system's efficiency significantly.
With normal air flow obstructed, air that bypasses the filter may carry dirt
directly into the evaporator coil and impair the coil's heat-absorbing capacity.
Filters are located somewhere along the return duct's length. Common filter
locations are in walls, ceilings, furnaces, or in the air conditioner itself.
Some types of filters are reusable; others must be replaced. They are available
in a variety of types and efficiencies. Clean or replace your air conditioning
system's filter or filters every month or two during the cooling season. Filters
may need more frequent attention if the air conditioner is in constant use, is
subjected to dusty conditions, or you have fur-bearing pets in the house.
Air Conditioner Coils.
conditioner's evaporator coil and condenser coil collect dirt over their
months and years of service. A clean filter prevents the evaporator coil from
soiling quickly. In time, however, the evaporator coil will still collect
dirt. This dirt reduces air flow and insulates the coil which reduces its
ability to absorb heat. Therefore, your evaporator coil should be checked
every year and cleaned as necessary. Outdoor condenser coils can also become
very dirty if the outdoor environment is dusty or if there is foliage nearby.
You can easily see the condenser coil and notice if dirt is collecting on its
fins. You should minimize dirt and debris near the condenser unit. Your dryer
vents, falling leaves, and lawn mower are all potential sources of dirt and
debris. Cleaning the area around the coil, removing any debris, and trimming
foliage back at least 2 feet (0.6 meters) allow for adequate air flow around
The aluminum fins on evaporator and condenser coils are easily bent and can block air flow
through the coil. Air conditioning wholesalers sell a tool called a "fin comb"
that will comb these fins back into nearly original condition.
Sealing and Insulating Air Ducts
An enormous waste of energy occurs
when cooled air escapes from supply ducts or when hot attic air leaks into
return ducts. Recent studies indicate that 10 percent to 30 percent of the
conditioned air in an average central air conditioning system escapes from the
For central air conditioning to be efficient, ducts must be airtight. Hiring
a competent professional service technician to detect and correct duct leaks is
a good investment, since leaky ducts may be difficult to find without experience
and test equipment. Ducts must be sealed with duct "mastic." The old standby of
duct tape is ineffective for sealing ducts.
Obstructions can impair the efficiency of a duct system almost as much as
leaks. You should be careful not to obstruct the flow of air from supply or
return registers with furniture, drapes or tightly fitted interior doors. Dirty
filters and clogged evaporator coils can also be major obstructions to air flow.
The large temperature difference between attics and ducts makes heat
conduction through ducts almost as big a problem as air leakage and
obstructions. Ducts in attics should be insulated heavily in addition to being
Buying New Air Conditioners Today's best air conditioners use 30 percent
to 50 percent less energy to produce the same amount of cooling as air
conditioners made in the mid 1970s. Even if your air conditioner is only ten
years old, you may save 20 percent to 40 percent of your cooling energy costs by
replacing it with a newer, more efficient model.
Air conditioners are rated by the number of British
thermal units of heat they can remove per hour. Another common rating term for
air conditioning size is the "ton," which is 12,000 British thermal units per
How big should your air conditioner be? The size of an air conditioner
- how large your home is and how many windows it has;
- how much shade is on your home's windows, walls and
- how much insulation is in your home's ceiling and
- how much air leaks into your home from the outside; and
- how much heat the occupants and appliances in your home generate.
An air conditioner's efficiency, performance, durability and initial cost
depend on matching its size to the above factors.
Make sure you buy the correct size of air conditioner. Two groups — the Air
Conditioning Contractors of America and the American Society of Heating,
Refrigerating, and Air Conditioning Engineers — publish calculation procedures
for sizing central air conditioners. Reputable air conditioning contractors will
use one of these procedures, often performed with the aid of a computer, to size
your new central air conditioner.
Be aware that a large air conditioner will not provide the best cooling.
Buying an oversized air conditioner penalizes you in the following ways:
- It costs more to buy a larger air conditioner than you
- The larger-than-necessary air conditioner cycles on and
off more frequently, reducing its efficiency. Frequent cycling makes indoor
temperatures fluctuate more and results in a less comfortable environment.
Frequent cycling also inhibits moisture removal. In humid climates, removing
moisture is essential for acceptable comfort. In addition, this cycling wears
out the compressor and electrical parts more rapidly.
- A larger air conditioner uses more electricity and creates added demands
on electrical generation and delivery systems.
Air Conditioner Efficiency
Each air conditioner has an energy-efficiency
rating that lists how many British thermal units per hour are removed for each
watt of power it draws. For room air conditioners, this efficiency rating is the
Energy Efficiency Ratio, or EER. For central air conditioners, it is the
Seasonal Energy Efficiency Ratio, or SEER. These ratings are posted on an Energy
Guide Label, which must be conspicuously attached to all new air conditioners.
Many air conditioner manufacturers are participants in the voluntary EnergyStar®
labeling program. EnergyStar-labeled appliances mean that they have high EER and
In general, new air conditioners with higher EERs or SEERs sport higher price
tags. However, the higher initial cost of an energy-efficient model will be
repaid to you several times during its life span. The Energy Office offers 5%
Dollar and Energy Saving Loans through local participating lenders for the
purchase of high efficiency air conditioners. Buy the most efficient air
conditioner you can afford, especially if you use an air conditioner frequently.
Air Conditioners — EER
Room air conditioners generally range from 5,500 to 14,000 British thermal
units per hour. National appliance standards require room air conditioners built
after January 1, 1990, to have an EER of 8.0 or greater. In Nebraska, the Energy
Office recommends a room air conditioner with an EER of at least 10.0.
The Association of Home Appliance Manufacturers reports that the average EER of
room air conditioners rose 47% from 1972 to 1991. If you own a 1970s-vintage
room air conditioner with an EER of 5 and you replace it with a new one with
an EER of 10, you will cut your air conditioning energy costs in half.
Central Air Conditioners — SEER.
standards for central air conditioners require a SEER of 9.7 and 10.0, for
single-package and split-systems, respectively. But you do not need to settle
for the minimum standard. There is a wide selection of units with SEERs
reaching nearly 17. In Nebraska, the Energy Office recommends the purchase of
a unit with a least of SEER of 12.0. Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0.
Replacing a 1970s-era central air conditioner with a SEER of 6 with a new unit
having a SEER of 12 will cut your air conditioning costs in half.
Hiring Professional Service
When your air conditioner needs more than the
regular maintenance described previously, hire a professional service
technician. A well-trained technician will find and fix problems in your air
conditioning system. However, not all service technicians are competent.
Incompetent service technicians forsake proper diagnosis and perform only
minimal stop-gap measures. Insist that the technician:
- check for correct amount of refrigerant;
- test for refrigerant leaks using a leak detector;
- capture any refrigerant that must be evacuated from the
system, instead of illegally releasing it to the atmosphere;
- check for and seal duct leakage in central systems;
- measure air flow through the evaporator coil;
- verify the correct electric control sequence and make
sure that the heating system and cooling system cannot operate simultaneously;
- inspect electric terminals, clean and tighten
connections and apply a non-conductive coating if necessary;
- oil motors and check belts for tightness and wear; and
- check the accuracy of the thermostat.
Choosing a Contractor
Choosing a contractor may be the most important
and difficult task in buying a new central air conditioning system. Ask
prospective contractors for recent references. If you are replacing your central
air conditioner, tell your contractor what you liked and did not like about the
old system. If the system failed, ask the contractor to find out why. The best
time to fix existing problems is when a new system is being installed.
When designing your new air conditioning system, the contractor you choose
- use a computer program or written calculation procedure
to size the air conditioner;
- provide a written contract listing the main points of
your installation that includes the results of the cooling load calculation;
- give you a written warranty on equipment and
- allow you to hold the final payment until you are satisfied with the new
Avoid making your decision solely on the basis of price. The quality of the
installation should be your highest priority, because quality will determine
energy cost, comfort and durability.
Installation and Location of Air
Conditioners If your air conditioner is
installed correctly, or if major installation problems are found and fixed, it
will perform efficiently for years with only minor routine maintenance. However,
many air conditioners are not installed correctly. As an unfortunate result,
modern energy-efficient air conditioners can perform almost as poorly as older
Be sure that your contractor performs the following procedures when
installing a new central air conditioning system:
allows adequate indoor space for the installation,
maintenance and repair of the new system, and installs an access door in the
furnace or duct to provide a way to clean the evaporator coil.
- uses a duct-sizing methodology such as the Air Conditioning Contractors of
America Manual D.
- ensures there are enough supply registers to deliver
cool air and enough return air registers to carry warm house air back to the
- installs duct work within the conditioned space, not in
the attic, wherever possible.
- seals all ducts with duct mastic and heavily insulates
- locates the condensing unit where its noise will not
keep you or your neighbors awake at night, if possible.
- places the condensing unit in a shady spot, if
possible, which can reduce your air conditioning costs by 1-2 percent.
- verifies that the newly installed air conditioner has
the exact refrigerant charge and air flow rate specified by the manufacturer.
- locates the thermostat away from heat sources, such as windows, or supply
If you are replacing an older or failed split system, be sure that the
evaporator coil is replaced with a new one that exactly matches the condenser
coil in the new condensing unit. The air conditioner's efficiency will likely
not improve if the existing evaporator coil is left in place. Iin fact, the old
coil could cause the new compressor to fail prematurely.
If you install a new room air conditioner, try to:
- locate the air conditioner in a window or wall area
near the center of the room and on the shadiest side of the house.
- minimize air leakage by fitting the room air conditioner snugly into its
opening and sealing gaps with a foam weatherstripping material.
Paying attention to your air conditioning system saves you money and reduces
environmental pollution. Notice whether your existing system is running
properly, and maintain it regularly. Or, if you need to purchase a new air
conditioner, be sure it is sized and installed correctly and has a good EER or
Using Your Air Conditioner
An air conditioner will cool the air in your home
fairly quickly. For economical operation, turn it on only when your home is
occupied. You may consider installing a programmable thermostat. These allow you
to set the time when the air conditioner will turn on, such as 30 minutes before
you arrive home from work on a hot day. During the day, keep the drapes or
blinds closed on windows that face east, south, and west. This will help reduce
solar heat gain into your home.