Your air conditioner works hard to keep your home cool and comfortable. When something goes wrong, especially during the hottest days of the year, it can quickly disrupt your routine.

Before calling in a professional, there are several simple troubleshooting steps you can try yourself. Many common AC problems are caused by minor issues that can be resolved in just a few minutes.

If your system still isn’t working after these checks, the experts at One Hour Heating & Air Conditioning® are available 24/7 to help.

AC Troubleshooting Checklist

If your air conditioner isn’t working properly, start with these quick troubleshooting steps before calling for service:

  1. Check thermostat settings
  2. Replace the air filter
  3. Make sure vents and registers are open
  4. Inspect for frozen evaporator coils
  5. Check the circuit breaker
  6. Look for water leaks or drain line clogs

1. Why Your AC Won’t Turn On

If your air conditioner won’t start, begin with the simplest possible causes.

  • Check the Thermostat Settings: Make sure your thermostat is set to 'Cool' and the temperature is set lower than the current room temperature.
  • Replace Thermostat Batteries: Weak or dead batteries can prevent your thermostat from sending the signal for your AC to start.
  • Reset the Thermostat: Some thermostat issues can be resolved by resetting the device to factory settings. Check the manufacturer’s instructions for your specific model.
  • Reset Window AC Units: If you have a window unit, unplug it for about 30 seconds and plug it back in to reset the system.

2. Poor or Weak Airflow

Reduced airflow can lead to uneven cooling, warm spots in your home, and increased strain on your system.

  • Check and Replace Air Filters: Dirty filters restrict airflow and can even cause evaporator coils to freeze. If you can’t see light through the filter, it’s time to replace it.
  • Inspect Vents and Registers: Make sure vents aren’t blocked by furniture, curtains, rugs, or other household items.

3. AC Running But Not Cooling: Common Causes

If your AC is running but the air coming from your vents isn’t cool, there may be a circulation or system issue.

  • Replace the Air Filter: A clogged filter can prevent cool air from moving through your home effectively.
  • Check for Frozen Evaporator Coils: Ice buildup on the coils can stop your system from cooling properly. Turn off the AC and allow the coils to fully thaw.
    • Evaporator coils are located inside your indoor HVAC unit, typically within or directly connected to the air handler or furnace. They’re most often found in utility closets, basements, attics, or other mechanical spaces. Access usually requires removing a service panel, though the exact location can vary by system.
  • Low Refrigerant: Low refrigerant levels—often caused by leaks—can prevent your system from producing cold air. HVAC technicians have the tools to measure refrigerant pressure. If your AC blows warm air, freezes up, or you hear hissing near the refrigerant lines, call a professional.
  • Dirty Condenser Coils: Outdoor condenser coils covered in dirt or debris can’t release heat properly, reducing cooling performance.

If cooling does not return after the coils thaw, the issue may involve refrigerant levels or the compressor, which require professional repair.

4. AC Short Cycling (Turning On and Off Frequently)

Short cycling occurs when your AC repeatedly turns on and off in short bursts. This can increase energy costs, strain the system, and lead to premature breakdowns.

Common causes include:

  • Oversized AC systems that cool too quickly and shut off repeatedly
  • Frozen evaporator coils caused by airflow restrictions or refrigerant problems
  • Dirty air filters that cause overheating and automatic shutdown
  • Refrigerant leaks that prevent the system from operating efficiently
  • Thermostat issues, such as poor placement or faulty sensors

If your AC frequently turns on and off, it’s best to contact an HVAC professional to diagnose the issue.

5. Why Your AC Is Leaking Water

Clogged condensate drain lines are a common issue and can cause water leaks or even shut down your AC system.

Signs your drain line may be clogged:

  • Your AC shuts off unexpectedly
  • Water is pooling near vents or ceilings
  • The drip pan is full or overflowing
  • Visible backup in the drain line

Why drain lines clog: Dust, dirt, mold, algae, and even insects can create blockages over time.

What you can try:

  • Carefully empty and clean the drip pan
  • Use a wet/dry vacuum to clear the drain line

If the clog remains, a technician can typically resolve the issue quickly during a service call.

6. AC Freezing Up

If you notice ice on your AC unit or refrigerant lines, your system may have frozen evaporator coils.

Common causes include:

  • Dirty air filters
  • Blocked airflow
  • Refrigerant leaks
  • Running the system in very cool outdoor temperatures

Turn off the system and allow the coils to thaw completely. If the problem continues, a technician should inspect the system.

7. AC Problems During Heat Waves

During periods of extreme heat, a malfunctioning AC system can become more than an inconvenience—it can pose a health risk, especially for children, older adults, and people with medical conditions.

  • Common AC failures during heat waves include:
  • Electrical issues preventing the system from starting
  • Refrigerant leaks that reduce cooling capacity
  • Sensor malfunctions causing inconsistent cooling
  • Drainage problems that trigger system shutdowns

If your AC stops working during extreme heat, treat it as an urgent issue and contact emergency HVAC service.

Still having ac issues? Find a professional near you written on One Hour banner

Still Having AC Problems?

If basic troubleshooting doesn’t solve the issue, One Hour Heating & Air Conditioning® is ready to help.

Our technicians provide:

  • 24/7 emergency service
  • Straightforward pricing
  • Fast, punctual repairs
  • Highly trained HVAC professionals

Schedule an appointment online or call (800) 893-3523 today.