How to Prevent Odor in a Swamp Cooler. Evaporative coolers are nicknamed swamp coolers because they can exude an unpleasant odor unless they're properly maintain. The aroma results from bacteria and fungi left in the reservoir over the summer. You can eliminate them with regular cleaning.
Check the condition of your cooler pads at the end of the summer. If there is a residue of mineral deposits, discard them and purchase new ones.
Clean the pad frames if necessary. Use a stiff wire brush to clear dirt, dust and mineral deposits.
Tip the cooler on its side and allow excess water to run out of the reservoir. Leave it in a secure area overnight, where water run-off isn't a problem (like a patio or porch).
Fill the reservoir with water and turn the unit on. Let it run until the pads get moist.
Notice whether there is an objectionable odor. If there is, add a capful of vinegar to the reservoir and let this process through until odor is gone.
Prevent future swamp cooler odors. Drain the reservoir thoroughly at the end of each summer.
Keep the unit covered during winter to protect it from dust and dirt.