# AC Not Cooling? 10 Common Causes and Solutions
When your AC stops cooling effectively, don't panic. Many issues have simple solutions you can try before calling for service.
Quick Diagnostic Steps
Before troubleshooting: 1. Check that the thermostat is set to "cool" 2. Verify the temperature is set below room temperature 3. Ensure the system has power 4. Wait 5 minutes if you just turned it on
Common Causes and Solutions
1. Dirty Air Filter **Symptoms:** Weak airflow, inadequate cooling, system running constantly
Solution: Check and replace your filter. This is the #1 cause of AC problems and the easiest to fix.
2. Thermostat Issues **Symptoms:** System doesn't turn on, wrong temperature reading
DIY Checks: - Replace batteries - Ensure it's not in direct sunlight - Check fan setting (should be "auto" not just "on") - Try setting temperature 5°F below room temp
3. Tripped Circuit Breaker **Symptoms:** System won't turn on at all
Solution: Check your electrical panel. Reset the breaker if tripped. If it trips again, call a professional.
4. Frozen Evaporator Coil **Symptoms:** Warm air, ice visible on refrigerant lines, water around indoor unit
Causes: - Dirty air filter - Low refrigerant - Blocked return air - Blower motor problems
What to Do: 1. Turn off AC 2. Run fan only for 2-3 hours to defrost 3. Check filter and airflow 4. Call for service if it refreezes
5. Dirty Condenser Coils **Symptoms:** AC runs but doesn't cool well, outdoor unit very hot
Solution: Turn off system and gently rinse outdoor coils with a garden hose. Remove debris around unit.
6. Low Refrigerant **Symptoms:** Warm air, hissing sound, ice on lines, high energy bills
Note: Low refrigerant indicates a leak. This requires professional service. Don't attempt DIY refrigerant charging.
7. Capacitor Failure **Symptoms:** AC hums but doesn't start, intermittent starting
Solution: This requires professional repair. Capacitors can be dangerous to handle.
8. Compressor Problems **Symptoms:** AC runs but doesn't cool, unusual sounds from outdoor unit
Solution: Professional diagnosis needed. Compressor issues can be serious.
9. Ductwork Leaks **Symptoms:** Weak airflow, some rooms not cooling, high bills
DIY Check: Feel for air leaking at visible duct connections. Professional duct sealing may be needed.
10. Undersized System **Symptoms:** AC runs constantly, never quite reaches set temperature, high bills
Note: If your AC has always struggled, it may be undersized for your home or cooling load.
When to Call a Professional
Call immediately if: - You smell gas or burning - You see smoke - Circuit breaker keeps tripping - Refrigerant lines are frozen - System makes grinding or squealing sounds
Schedule service for: - Warm air that doesn't improve with filter change - Recurring problems - Annual maintenance (prevents most issues)
Preventive Measures
Monthly - Check and replace filters - Clear debris from outdoor unit
Annually - Professional tune-up - Duct inspection - Coil cleaning
Every 3-5 Years - Duct cleaning - Ductwork inspection and sealing
Bay Area Specific Issues
Coastal Homes Salt air can corrode outdoor units faster. More frequent coil cleaning helps.
Older Homes Aging systems and ductwork are common. Consider upgrade if system is over 15 years old.
Wildfire Season Heavy smoke can clog filters quickly. Check weekly during smoke events.
Troubleshooting Checklist
- [ ] Check thermostat settings
- [ ] Check/replace air filter
- [ ] Check circuit breaker
- [ ] Inspect outdoor unit for debris
- [ ] Look for ice on refrigerant lines
- [ ] Feel airflow at vents
- [ ] Listen for unusual sounds
If you've tried these steps and your AC still isn't cooling properly, contact us for professional diagnosis. Most issues can be resolved same-day with the right expertise and parts.