The evaporator for the central air system is located directly above the furnace in the plenum. The evaporator may not be accessible, but if it is, you should clean it once a year. If the plenum has foil-wrapped insulation at its front, you can clean the evaporator; if the plenum is a sealed sheet metal box, do not attempt to open it. Here's how to clean an accessible evaporator:
Step 1: Remove foil-wrapped insulation at front of plenum; it's probably taped in place. Remove tape carefully, because you'll have to replace it later. Behind insulation is access plate, which is held in place by several screws. Remove screws and lift off plate.
What You'll Need
You'll want to have these tools on hand to clean the evaporator:
Step 3: Clean tray below evaporator unit. This tray carries condensation away from evaporator. Pour 1 tablespoon of household bleach into weep hole in tray to prevent fungus growth. In extremely humid weather, check condensate drain and pan every other day. If there's much moisture in pan, weep hole from pan to drain line may be clogged. Open weep hole with piece of wire.
Step 4: Put unit back into place, reinstall plate, and tape insulation back over it.
Step 5: Turn back on air conditioner, and check for air leaks. Seal any leaks with duct tape.
You also may need to clean the condenser to get your air conditioning functioning properly. Find out how on the next page.