Basic Maintenance for Your Central Air

Central air conditioning systems consist of an outside unit with a compressor, condenser coil and fan, and an interior evaporator coil installed in the supply duct of a warm-air furnace. Indoor heat is picked up and carried through pipes by a refrigerant to the condenser coil outside. Although air conditioners don't need a full seasonal tune-up the way most furnaces do, some basic maintenance will maximize cooling output. The well-maintained unit runs more efficiently, lasts longer, and makes rooms feel cooler at a lower, money-saving setting on the thermostat.

The procedure for cleaning a central air system, illustrated below, is similar to that for a room unit, except that the machines are bigger, and the parts may be harder to reach - even though on most systems they are split into two sections. Before attempting anything more than superficial cleaning, turn off the electrical power and follow the manufacturer's directions for discharging the capacitor, an electrical storage device that can deliver a shock even after electrical power has been cut off to the unit. Most owner's manuals contain a great deal of specific information on the care of the unit as well as schematics giving the location of the parts that are involved.

To clean the condenser fan and oil the fan motor (both in the outside unit), you will probably have to remove a cover grille, loosen a setscrew holding the fan on the motor shaft, and then remove the fan to gain access to oil ports on the motor. Use a garden hose to clean the outside condenser coils, but only after removing the coil guard so you can spray from inside the unit. Otherwise, water-soaked debris will lodge in the fins. If the fins are bent against each other, which is more likely on exterior coils set away from the protection of the building, it's best to use a specialized tool called a fin comb to clean and straighten them.

Homeowners can take care of the basic maintenance of a central air conditioner system but you need a professional to service the compressor and to recharge the refrigerant. The refrigerant in older air conditioners is typically Freon, an ozone-damaging hydrochlorofluorocarbon (HCFC). Eventually, the closed refrigerant loop can develop a slow leak and cause the compressor to fail prematurely. As it's illegal to release HCFCs into the atmosphere, when an older machine needs repair, the service contractor is required to capture and recycle the refrigerant. Recycled HCFCs are used to recharge older machines. Most new models use less-damaging refrigerants.
Project Basics


Estimated Project Time:
1 hour

Start Tips:
Trim bushes and other vegetation from around outside unit

Safety Tips:
Turn off electrical power to the system and discharge the capacitor before working on the unit


Tools and Materials:

Plastic sheets
Garden hose
Soft brush

Fin comb or straightening tool
Nondetergent motor oil
New air filters, as needed


Fig. 1

1) Turn Off Power
The first step is to shut off electrical power to the unit. Most systems have a cutoff box mounted outside near the fan unit. (Fig. 1) Follow the manufacturer's directions for discharging the capacitor, an electrical storage device that can deliver a shock even after power has been cut off.

Fig. 2

2) Clean the Grilles
Remove the access panel. (Fig. 2) Use a garden hose and brush to clear any debris or grass clippings from the cabinet grilles. Spray from the inside out; if necessary cover electrical parts with plastic.

Fig. 3

3) Clean and Lubricate the Fan
Clean the fan blades and fan motor housing, and lubricate the motor with oil as required by the manufacturer. Typically, fan motors get two or three drops of nondetergent motor oil in each port, but follow the manufacturer's oiling guidelines as well as other cleaning and maintenance procedures. Remove any debris you find. (Fig. 3)

Fig. 4

4) Clean and Straighten Fins
Use a soft brush to clear dust from the coil fins. (Fig. 4) Take care not to compress these delicate rows of metal fins, which must be separated to transfer temperature efficiently. If some fins are bent use a fin comb or straightening tool to align them. One of several sets of small teeth arranged around the tool head will fit between undamaged fins above the bent area. As you pull the tool downward, its teeth will separate the compressed fins.

Fig. 5

5) Change the Filters
One of the easiest steps, but one of the most important, is to clean or change the air filters that keep dust out of the duct system. (Fig. 5) Either wash or replace the filters according to the manufacturer's directions.