Maintaining and Troubleshooting a Central Air Conditioner

by Steve Cory

If your home has central air conditioning, you can do much of the AC maintenance yourself; you can even fix a few problems. Here’s what to do to care for your central AC system, when to do that care and when to call a professional.

Central AC Basics

A central air conditioner has two main components. The condenser sits on a concrete slab outside the house. The evaporative coil is inside the house, in the plenum, which is the main duct from which all the other ducts branch toward the individual rooms. If you have a forced-air heating system, this plenum is just above the furnace.

Replace the Filter

Replacing the filter is both easy and essential. A clean air filter helps your AC run efficiently. Change the filter — or clean it, if you have a washable filter — at the beginning of the cooling season at the very least. Inspect it monthly and change it if needed. See Change a Furnace Filter for instructions (if you have a forced-air furnace, the same filter serves the AC).

Care for the Condenser

A condenser works most efficiently when air can move freely around and through it, and when it’s protected from harm.

Keep the outside clean. Wash the outside panels with soapy water and wipe the grill that protects the fan with a damp rag. Rub any rust with sandpaper and apply metal primer.

Clean the condenser coils. Condenser coils are small serpentine tubes that run through a grid of metal fins. At least once a year and at the beginning of the cooling season, shut off power to the condenser and remove the grill and the metal panels. Completely cover the fan, compressor and all electrical parts with a plastic bag. Vacuum away all loose dirt, and then use a soft brush and a garden hose with a spray attachment to thoroughly clean the coils. Work gently, so you don’t bend the fins.

Clear the area. Trim bushes and low tree branches so they’re at least two feet away from the condenser. If you build a screen to hide the condenser, make its walls partially open — perhaps use lattice. When mowing or leaf blowing nearby, take care not to shoot grass clippings, leaves or other debris towards the condenser.

Protect the condenser. Cut away any nearby branches that might fall on the condenser. During the winter, cover the condenser.

Clean the Evaporator

The evaporator should be cleaned at least once a year. If yours is inside a sealed sheet-metal box, don’t open it yourself; call in a certified heating and cooling professional. However, if it’s covered with foil-wrapped insulation, you can clean it yourself:

1. Carefully pull back the duct tape or foil tape that holds the insulation in place; you may be able to reuse the tape, or you might need new tape to reseal it.
2. Use a brush to clean the underside of the evaporator. To gain better access, pull it out gently, taking care not to bend any pipes. A small mirror may help you see the parts in the back.
3. Clean the drain tray, which carries condensation away from the evaporator. Disconnect the drain line that attaches to it and flush the tray with a hose. If the drain hole is completely clogged, use wire to unclog it. Pour in a tablespoon of household bleach to prevent mold and algae and reattach.
4. Replace the insulation and seal it with the same type of tape. If you use duct tape be sure to use professional tape, not general purpose. Turn the air conditioner on and apply more tape if you find any air leaks.

Schedule a Professional Inspection

It’s important to have a heating and cooling specialist inspect your condenser at least every other year. If your evaporator is inaccessible, call in a pro every year to clean it. Also call a pro in case of the following:

• You hear hissing at the condenser, which can indicate a leak.
• You see evidence of dripping oil, which also indicates a leak.
• The condenser stays on for longer than usual, which may indicate low refrigerant.

Tag along and ask questions, so you can perform some maintenance procedures yourself in the future.

Dealing with Problems

If your air conditioner is acting up, there are a couple of steps you can take before calling in a service professional.

Air condition doesn’t turn on. If the air conditioning does not come on at all, do the following:

1. Check that it’s switched on — the switch is usually outside, in a metal box next to the condenser. Allow 24 hours after turning on the condenser before turning on the thermostat.
2. If it’s not the switch, make sure the thermostat is set to Cool or Auto with the temperature below the room temperature.
3. If that doesn’t work, check to see if a circuit breaker needs to be reset.
4. If it still doesn’t operate, call for service.

The condenser clatters. The fan may be loose or hitting the grill.