Air Conditioning

When your air conditioner needs more than regular maintenance, 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 nor professional.

We recommend that you insist that your 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 any part of your system that runs in the attic, crawl, or garage
• 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
• Check the accuracy of the thermostat

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 should:

• Use a written calculation procedure or computer program 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 workmanship.

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.

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 inefficient models.

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 (ACCA) 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 air conditioner.
• Installs duct work within the conditioned space, not in the attic, wherever possible – insulating it where it must be run outside the treated structure.
• Seals all ducts with duct mastic and heavily insulates attic ducts.
• 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% to 2%.
• 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 registers.

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; in 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 weather stripping 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 SEER rating.

Unless, your contractor has sized your air conditioner to maximize humidity control instead of just cooling the air temperature, an air conditioner will cool the air in your home fairly quickly. For economical operation, turn it on only when your home is occupied. We also recommend that, 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.

To save more money, we suggest installing a programmable thermostat. These allow you to set the time when the air conditioner will turn on before you arrive home from work on a hot day. You can also choose to program your thermostat to run your systems are minimal settings, if not simply turning them off completely, while you are away on vacation.

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 airflow and reduce a system’s efficiency significantly. With normal airflow 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 pets in the house.

The air 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 allow for adequate airflow around the condenser.

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% to 30% of the conditioned air in an average central air conditioning system escapes from the ducts.

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 many times 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 airflow.

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 made airtight.

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 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 need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit.

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., 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.

Each air conditioner has an energy-efficiency rating that lists how many Btu 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 (see Source List in this publication). EnergyStar®-labeled appliances mean that they have high EER and SEER ratings.

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. Your utility company may encourage the purchase of a more efficient air conditioner by rebating some or all of the price difference. Buy the most efficient air conditioner you can afford, especially if you use (or think you will use) an air conditioner frequently and/or if your electricity rates are high.