How to replace the filters, clean the condenser, and get your AC unit into tip-top shape.

By Don Vandervort, HomeTips

On the first really hot day of summer, the last thing you want is to flip the switch on your central air conditioner only to find that it doesn’t work.

When an air conditioner sits idle for months, collecting leaves and debris, a bit of maintenance is often needed to get it running properly. If you don’t do this maintenance before summer arrives, you may end up waiting several hot days for a busy service pro—and paying top-of-the- season prices, to boot. Now is the time to get your A/C system working well.

A central air-conditioning system employs two main components: a condenser unit, which is typically located outdoors, and an evaporator unit mounted on the air handler or furnace. Together these extract heat from room air through refrigeration technology. The air handler or furnace blower blows the resulting chilled and dehumidified air through ductwork to the home’s rooms.

Materials & Tools HomeTips Recommends for This Project
MATERIALS	TOOLS Rent Tools Here
A/C or Furnace Filter Air Conditioner Coil Cleaner Lubricating Oil	Air Conditioner Fin Comb Hose Nozzle - Pistol Grip Nut Driver Set Refrigerator Coil Brush Screwdriver Set Utility Knife Vacuum Cleaner Work Gloves

(For more about how an A/C system works, see How a Central Air Conditioner Works.)

Repairs to a central air conditioner’s sealed refrigeration system are not a do-it-yourself job. They should be handled by a professional HVAC service pro. You can, however, do certain cleaning and maintenance tasks yourself to ensure efficient operation and keep the need for professional servicepeople to a minimum. Some of those tasks are detailed below.

Before working on a central air conditioner, always turn off the power to the condenser at the service panel. The condenser also typically has a 240-volt weatherproof disconnect box located near the unit; this contains a lever, fuses, or a circuit breaker to shut off the condenser. Turn this off, too.

(Note: The condenser contains a capacitor that stores an electrical charge and can be dangerous; allow about a half hour for the charge in the capacitor to dissipate.

As an added precaution, avoid touching all electrical components. The furnace or air-handler cabinet often has a separate switch or a circuit breaker in the main electrical panel to control it. Shut this off, too.)

1) Clean or replace filters. Clean or replace your furnace or air-handler filters twice a year or whenever they begin to look clogged with dust. If you don’t, air flow will be restricted, reducing efficiency, and you will recirculate dust into your home.

The filter is usually located inside or very near the return-air (air- inlet) side of the furnace or air- handler cabinet; in some cases, filters are in return-air registers located inside the home’s rooms, as shown here. Replace a disposable filter like this one or clean a reusable filter according to the manufacturer’s directions.

2) Clean the air-conditioner condenser. A central air conditioner’s condenser unit, typically located outdoors, is like a large fan in a metal box with sides that look like grilles. Ideally, it is protected through the winter by a condenser cover or tarp to prevent accumulation of debris inside it. Otherwise, it is likely to contain leaves, yard debris, and dirt—and you will need to clean it.

A large fan inside the metal box moves air across radiator-style condenser coils. If debris has gotten inside the unit, dirt has probably clogged some of the coils, as shown below. Anything that obstructs the flow of air will cut down the condenser’s efficiency, so these coils should be cleaned at the beginning of every cooling season if they are clogged.

To clean the coils, you’ll need to remove the side and top panels or protective grilles from the condenser unit, using a screwdriver or nut driver, depending upon the type of fasteners used. Be sure the power to the unit is turned off before you open up the condenser. Just unscrew the side panels and pull them away from the unit, then lift off the top, which may be heavy due to the weight of the fan attached to it. Don’t tug any of the wires connected to it.

Using a refrigerator coil brush or a soft brush on a vacuum, gently clean the coils from the outside of the unit. Be careful not to bend the delicate fins or damage the coils. If you do bend the fins, you can straighten them with a “fin comb” made for this purpose. After cleaning from the outside, vacuum the coils from the inside.

To release stubborn debris, spray on a commercial coil cleaner from the inside, being careful not to spray the fan or electrical components. Sometimes it’s necessary to use a hose with a trigger-style nozzle to blast dirt and debris out of the coils from inside the unit with a strong but focused stream, but be very careful if you do this. Do not bend the fins, flood the area, or spray water on electrical components or the fan motor so cover those parts with a plastic garbage bag. Also be aware that doing this can cause mud to block some of the areas between the fins, so you will need to be thorough.

Scoop leaves and debris out of the base of the condenser and, if it has a drain, make sure the drain is clear.

Use the vacuum and a rag to clean the blower’s fan blades. Then tighten any loose mounting bolts and, if the fan motor has oil ports, put a few drops of lightweight oil into the ports for lubrication. Mop up any excess water inside the unit with a rag, and then reassemble the condenser.

Cut and remove any weeds or vines that may obstruct airflow through the condenser unit.

Allow the unit to dry thoroughly and then turn the power to the condenser back on by doing the following: 1) Turn the thermostat in your home to “Off.” 2) Turn on the power at both the disconnect box and at the main panel. 3) Switch the thermostat to “Cool.”

3) Check the coolant lines. The refrigerant tubes or pipes that run from the evaporator on the air handler to the condenser outside are typically covered with foam coolant line insulation to prevent them from losing energy. If you see areas where the insulation is frayed or missing, replace it. To do this, wrap the lines in a spiral fashion with foam insulation tape, which you can cut with a utility knife.