Bad odors from evaporative coolers are common but fixable. Here are the causes and solutions:
Common causes of odor:
1. Stagnant water
- Water sitting in the reservoir breeds bacteria
- Creates a "swampy" or musty smell
- Solution: Drain and refill water at least weekly; don't let water sit unused for days
2. Moldy or dirty pads
- Pads that stay constantly wet can grow mold
- Mineral deposits trap organic matter
- Solution: Replace pads if moldy; run fan-only for 30 minutes after cooling to dry pads
3. Algae growth
- Green slime in the reservoir or on pads
- More common in sunny locations
- Solution: Clean reservoir monthly; use algaecide tablets
4. Dead animals or debris
- Birds, mice, or insects sometimes get into coolers
- Leaves and organic debris decompose
- Solution: Clean and inspect cooler thoroughly; install screens
5. Bacterial buildup
- Biofilm develops in water lines and pump
- Creates persistent musty odors
- Solution: Flush system with diluted bleach or cooler treatment
How to eliminate odors:
Immediate fix: 1. Turn off the cooler 2. Drain all water 3. Remove and inspect pads (replace if moldy) 4. Scrub the reservoir with a brush and mild bleach solution 5. Rinse thoroughly 6. Refill with fresh water 7. Add cooler treatment tablets
Ongoing prevention:
- Drain water weekly
- Use water treatment monthly
- Run fan-only after cooling sessions
- Clean reservoir monthly during season
- Replace pads at least annually
- Don't cover the unit while wet
When to call a professional:
- If odors persist after thorough cleaning
- If you suspect dead animals inside
- If there's visible mold throughout the system
- If the cooler has been neglected for years
