If your air conditioner is beginning to smell, then it's time to find and clear the source of the bad odor. Air conditioning odors usually come from mold and mildew that accumulate from condensation on the refrigerator coils, in a clogged drain pan, or leak in the system. But, animals can also get in the unit and die, creating a really bad odor. You'll need to check for both conditions before cleaning. If you have a window unit, cleaning is a little easier.
Step 1 - Check Your Air Conditioning Unit
Depending on the style and model, open the covers, top or access panels of your air conditioning unit. Using a flashlight, look inside the unit for signs of what might be causing the odor. Look for any dead animals (mice, rats, bats, squirrels, or snakes,), decaying vegetation, mold or mildew. If you have a window unit, remove the unit from the window and place it on the ground or a flat outdoor surface. Removing access panels to a window unit may take a little more work because of the amount of screws. Draw a diagram to indicate what screws and snaps go to what panel to make reassembly easier.
Step 2 - Clean Your Air Conditioning Unit
While wearing latex gloves, remove any visible debris or dead animals you can reach. When you've removed as much of any debris you can find, use your foaming coil cleaner and spray the air conditioner's coil. Allow the foam to work for about 10 to 15 minutes. This should loosen any dirt, oil or grime. Rinse until the water from the unit runs clear. Repeat if necessary.
Step 2 - Flush Your Drain Line
Find and remove your air conditioner's condensation drain line. Flush the line with bleach and hot water, or with undiluted distilled white vinegar if you don't want to use bleach, to kill any fungi, mold or mildew that may be in the line. Allow the line to dry. While you have the line off, install a three-way clean-out valve to allow for future cleaning without having to remove the line. In a window unit you won't have a line, but will be able to see the built in drain pan and drainage hole. Make sure the pan and hole are clean. Use an old toothbrush if needed.
Step 3 - Clean Your Drain Pan
Find the drip or drain pan or tray. Remove and wash thoroughly with hot, soapy water. Rinse with diluted bleach solution or undiluted white distilled vinegar if you don't want to use bleach. Allow pan to dry. Replace the pan.
Step 4 - Replace Filter
Find and replace, any filters in your unit. If your unit uses reusable filters clean them with hot soapy water and rinse with a diluted bleach solution of 1 part bleach to 10 parts water. Check the old filters for mold and mildew.
Step 5 - Check the Results
After cleaning your air conditioner, turn it back on and test the air with a few sniffs. If the odor persists, your problem may be in your duct-work.