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A building’s central air-conditioning system must be periodically inspected and maintained in order to function properly. While an annual inspection performed by a trained professional is recommended, homeowners can do a lot of the work themselves by following the tips offered here.

Clean the Exterior Condenser Unit and Components

The exterior condenser unit is the large box located on the side of the house that’s designed to push heat from the indoors to the outdoors. Inside of the box are coils of pipe that are surrounded by thousands of thin metal “fins” that allow the coils more surface area to exchange heat. 

Follow these tips when cleaning the exterior condenser unit and its inner components — after turning off power to the unit, of course.

• Remove any leaves, spider webs and other debris from the unit’s exterior. Trim foliage back several feet from the unit to ensure proper air flow.
• Remove the cover grille to clean any debris from the unit’s interior. A garden hose can be helpful for this task.
• Straighten any bent fins with a tool called a fin comb.
• Add lubricating oil to the motor. Check your owner’s manual for specific instructions.
• Clean the evaporator coil and condenser coil at least once a year. When they collect dirt, they may not function properly.

Inspect the Condensate Drain Line

Condensate drain lines collect condensed water and drain it away from the unit.  They’re located on the side of the inside fan unit. Sometimes there are two drain lines—a primary drain line that’s built into the unit, and a secondary drain line that can drain if the first line becomes blocked. 

Homeowners can inspect the drain line by using the following tips, which take very little time and require no specialized tools:

• Inspect the drain line for obstructions, such as algae and debris. If the line becomes blocked, water will back up into the drain pan and overflow, potentially causing a safety hazard or water damage to your home.
• Make sure the hoses are secured and fit properly.

Clean the Air Filter

Air filters remove pollen, dust, and other particles that would otherwise circulate indoors. Most filters are typically rectangular in shape and about 20 x 16 inches, and about 1 inch thick. They slide into the main ductwork near the inside fan unit. The filter should be periodically washed or replaced, depending on the manufacturer’s instructions. A dirty air filter will not only degrade the quality of the home indoors, but it will also strain the motor to work harder to move air through it, increasing energy costs and reducing energy efficiency. The filter should be replaced monthly during heavy use during the cooling seasons. You may need to change the filter more often if the air conditioner is in constant use, if any family members have respiratory problems if you have pets with fur, and/or if it’s particularly dusty indoors.  

Close the Air-Distribution Registers

Air-distribution registers are duct openings in ceilings, walls and floors where cold air enters the room. They should be closed after the cooling season ends in order to keep warm air from back-flowing out of the room during the warming season. Pests and dust will also be unable to enter the ducts during the winter if the registers are closed. These vents can typically be opened or closed with an adjacent lever or wheel.  Remember to open the registers in the spring before the cooling season starts.  Also, make sure they’re not blocked by drapes, carpeting or furniture.

In addition, homeowners should practice the following strategies in order to keep their central air-conditioning systems running properly:

• Have the air-conditioning system inspected by a professional each year before the start of the cooling season.
• Reduce stress on the air-conditioning system by enhancing your home’s energy efficiency. Switch from incandescent lights to compact fluorescents, for instance, which produce less heat.

Thermostats

Thermostats are devices designed to control the heating and cooling system in the home so that the air temperature remains comfortable. Homeowners should understand how thermostats operate, as well as the more common problems associated with them. 

Thermostats can be manually controlled or set to activate automatically based on timers or room temperature readings. Most thermostats contain two meters:  the “set” temperature that the thermostat is asking for, and the actual temperature. On a traditional dial-type thermostat, the user can increase the set temperature by rotating the dial clockwise, and lower it by rotating it counter-clockwise. Newer thermostats usually have digital displays, which can be used to adjust automated heating and cooling schedules. 

Location

In order to avoid false or “ghost” readings, which will cause unnecessary furnace or air-conditioner cycling, the thermostat must be installed so that it correctly reads the room temperature. 

The following locations may cause the thermostat to give false readings: 

• near a heat source, such as a fireplace, hot water pipes, bright lights, direct sunlight, and electrical appliances that produce heat;  
• in a drafty hallway, or near a window or exterior door that is left open often; and
• on an outside wall. Outside walls are affected too much by outside temperatures, which may make the thermostat “think” the air in the house is warmer or cooler than it really is.

Common Thermostat Problems and Solutions

• erratic operation or fluctuating temperature. This is often caused by poor pin connections between the thermostat and the backplate when the backplate is flexed against an uneven wall. To allow the backplate to flatten out, loosen the screws that attach the backplate to the wall, then snap the thermostat back onto the backplate. 
• a thermostat that doesn’t respond to changes in room temperature. This can happen when there is air passing over the temperature sensor from a hole in the wall behind the thermostat, through which wires enter from the air-handling unit. To rectify this, insulate the hole behind the thermostat with fiber insulation, spray foam, or any other insulating material. 
• a temperature reading that is inaccurate. A convenient way to test the temperature sensor is to tape a thermometer to the wall next to the thermostat and wait 15 minutes. A faulty thermometer needs to be recalibrated. Instructions for recalibration vary by manufacturer. 
• loss of power. This may be caused by the following two situations:
  1. If the air handler powers the thermostat, check the circuit breaker meant for the air handler and make sure it has not tripped.
  2. If batteries power the thermostat, make sure they are lithium, not alkaline. Alkaline batteries will die rapidly or cause erratic thermostat operation.

Maintenance and Other Tips

• Give the thermostat’s interior a light dusting with a small, soft-bristle paintbrush. Canned air can also be used to blow off dust. Twist the screws to remove the cover. Be sure to clean the contacts, which are small metal plates within the unit. The wires coming from the transformer attach to the contacts. Do not touch any of the interior parts with your fingers. 
• If the base is loose, re-tighten the screws. Check the wires coming from the transformer. If any corrosion is present, remove the wire from the contact and clean it. Use a wire stripper to remove the surrounding insulation, cut back the wire, and reconnect it. 
• Make sure the terminal screws are tight. 
• For wireless thermostats, make sure the model number of the thermostat matches the model number of the receiver. If the model numbers don’t match, the thermostat and receiver will not be compatible and won’t function properly together. 
• Make sure that your thermostat has been set to the proper position for the season: cooling or heating. The air conditioner will not run with the switch set to “heating” and, conversely, the heating system won’t run if the thermostat has been set to “cooling.”
• Thermostats that contain a mercury switch must remain perfectly level or they may not control the temperature setting. 

A Few Notes on Energy Savings

• Many people believe that furnaces work harder than normal to warm an area back up to a comfortable temperature, which will counteract energy savings gained from turning the thermostat down. This belief is a misconception that has been disproved by years of studies and research. Fuel is saved between the time the temperature is stabilized at the lower level and the next time heat is needed, while the fuel required to re-heat the space is roughly equal to the fuel saved while the building drops to a lower temperature. 
• According to the U.S. Department of Energy, consumers can save 10% on their utility bills by setting their thermostat lower by 10° to 15° for eight hours. This can be easily accomplished with a programmable thermostat. 
• Be careful not to set the thermostat so low in the winter that indoor plumbing pipes freeze, or so low during the summer that mold may be allowed to grow prompted by excess indoor humidity.  

Programmable Thermostats

Using a programmable thermostat in the winter, you can automatically turn down your heat at night or when you’re not at home.  In the summer, you can save money by automatically turning your air conditioner up at night or when you’re at work. 

Using a programmable thermostat, you can adjust the times that the heating and air conditioner go on and off according to a preset schedule. As a result, the equipment doesn’t operate as much when you’re asleep or when the house (or a part of it) is empty. Programmable thermostats can store and repeat multiple daily settings (six or more temperature settings a day) that you can manually override without affecting the rest of the daily or weekly program.