Is Your Air Conditioner Acting Up? Start Here.

Before you call a technician, many common air conditioner problems have straightforward causes that you can identify — and sometimes fix — yourself. This guide covers the most frequent AC issues homeowners encounter and what to do about each one.

1. AC Won't Turn On

Possible causes: Tripped circuit breaker, blown fuse, thermostat issue, or power outage.

What to do: Check your circuit breaker and reset it if tripped. Confirm the thermostat is set to "Cool" and the temperature is set below room temperature. Replace thermostat batteries if applicable. If none of these work, call a technician.

2. AC Runs But Doesn't Cool

Possible causes: Dirty air filter, low refrigerant, frozen evaporator coil, or dirty condenser coils.

What to do: Replace or clean the air filter first — it's the most common culprit. Check if the outdoor unit is running. If the system runs but blows warm air, you may have a refrigerant leak, which requires a licensed HVAC technician.

3. AC Is Freezing Up (Ice on the Unit)

Possible causes: Restricted airflow (dirty filter), low refrigerant, or running the AC in very cold outdoor temperatures.

What to do: Turn off the AC and let it thaw completely (this may take several hours). Replace the filter and check all vents are open. Restart and monitor. If it freezes again, call a pro — you likely have a refrigerant issue.

4. AC Is Leaking Water Inside

Possible causes: Clogged condensate drain line, frozen evaporator coil melting, or improper installation.

What to do: The condensate drain line can often be cleared with a wet-dry vacuum or by flushing with a diluted vinegar solution. If water is pooling heavily, shut the system off and call a technician to prevent water damage.

5. AC Makes Strange Noises

  • Banging or clanking: Loose or broken parts inside the compressor or fan. Stop using the unit and call a technician.
  • Squealing or screeching: Often a worn fan belt (in older units) or a failing motor bearing.
  • Clicking repeatedly: Could indicate a failing relay, capacitor issue, or debris in the outdoor unit.
  • Hissing: May suggest a refrigerant leak — a serious issue requiring professional attention.

6. AC Smells Bad

  • Musty/moldy smell: Mold or mildew in the ductwork or on the evaporator coil. Clean or replace filters; consider a professional coil cleaning.
  • Burning smell: Overheating motor or electrical issue. Shut the unit off immediately and call a technician.
  • Rotten egg smell: Could indicate a gas leak nearby (not AC-related). Evacuate and call your gas company.

7. AC Short Cycles (Turns On and Off Rapidly)

Possible causes: Oversized unit, dirty filter, low refrigerant, or a failing thermostat.

What to do: Replace the filter. Check thermostat placement — it shouldn't be near heat sources or drafts. If the problem persists, a technician will need to assess refrigerant levels and equipment sizing.

8. Rooms Are Unevenly Cooled

Possible causes: Poor duct design, blocked vents, inadequate insulation, or an undersized system.

What to do: Ensure all vents are open and unblocked. Check attic and wall insulation. Consider a mini-split for problem rooms, or have a duct inspection performed.

9. High Energy Bills

Possible causes: Aging inefficient unit, dirty filters/coils, refrigerant issues, or poor home insulation.

What to do: Clean or replace filters monthly during peak season. Schedule annual maintenance. If the unit is over 15 years old, evaluate replacement versus repair.

10. Thermostat Isn't Working Properly

Possible causes: Dead batteries, incorrect placement, miscalibration, or faulty wiring.

What to do: Replace batteries. Ensure the thermostat isn't in direct sunlight or near heat-producing appliances. Consider upgrading to a smart thermostat for more reliable performance.

When to Call a Professional

If your troubleshooting doesn't resolve the issue, or if you suspect a refrigerant leak, electrical fault, or compressor failure — always call a licensed HVAC technician. Attempting complex repairs without proper training can be dangerous and may void your warranty.