AC Running but Not Cooling? Here’s What’s Wrong

When your air conditioner is running but your home still feels hot, it’s more than frustrating—it’s a sign something isn’t working the way it should. In a climate like San Antonio, even a short cooling issue can quickly turn into an uncomfortable (and stressful) situation.

Last Updated

January 7, 2026

The good news? This problem is common, and many causes are identifiable once you know what to look for. Below, we’ll walk through the most common reasons an AC runs without cooling, what you can safely check yourself, and when it’s time to call a professional.

Common Reasons Your AC Is Running but Not Cooling

Dirty or Clogged Air Filter

A clogged air filter is one of the most frequent causes of cooling issues. When airflow is restricted, your system can’t move enough air across the cooling coil, reducing its ability to cool your home.

What happens:

  • Reduced airflow
  • Uneven cooling
  • Increased strain on the system

Changing your air filter regularly helps maintain proper airflow and system performance.

Thermostat Settings or Malfunctions

Sometimes the issue isn’t the AC itself—it’s the thermostat.

Check for:

  • Thermostat set to “fan only” instead of “cool”
  • Temperature set higher than expected
  • Dead batteries or unresponsive controls

If the thermostat isn’t communicating correctly with the system, your AC may run without delivering cold air.

Low Refrigerant Levels

Refrigerant is what allows your AC to absorb heat from inside your home. If levels are low, the system can’t cool effectively.

Common causes:

  • Refrigerant leaks
  • Aging systems
  • Improper previous repairs

Low refrigerant isn’t a DIY fix and should always be handled by a licensed professional.

Frozen Evaporator Coil

Restricted airflow or low refrigerant can cause the indoor coil to freeze. When this happens, the system may run but won’t cool properly.

Signs of a frozen coil:

  • Warm air from vents
  • Ice visible on refrigerant lines
  • Reduced airflow

Turning the system off can prevent further damage, but professional HVAC service is usually required.

Dirty Condenser Coils (Outdoor Unit)

Your outdoor unit releases heat from your home. If the condenser coil is covered in dirt, grass, or debris, heat can’t escape efficiently.

Results include:

  • Poor cooling performance
  • Longer run times
  • Higher energy bills

Keeping the area around the outdoor unit clear is essential for proper operation.

Electrical or Capacitor Issues

AC systems rely on electrical components like capacitors and contactors to start and run correctly. When these fail, the system may partially operate without cooling.

This type of issue requires professional diagnosis and repair.

Things You Can Check Before Calling a Professional

Before scheduling service, there are a few safe checks homeowners can do:

  • Replace or clean the air filter
  • Confirm thermostat settings
  • Check the circuit breaker
  • Clear debris around the outdoor unit

If these steps don’t restore cooling, it’s time to call an HVAC professional.

When to Call an HVAC Professional

You should contact a professional if you notice:

  • Warm air blowing from vents
  • Ice buildup on the system
  • Burning or electrical smells
  • Loud or unusual noises
  • The system running constantly without cooling

Continuing to run a malfunctioning AC can lead to more expensive repairs or system failure.

Repair vs. Replacement: What Makes Sense?

Not every cooling issue means you need a new system—but sometimes AC replacement is the smarter long-term choice.

Repair may make sense if:

  • The system is under 10 years old
  • The issue is isolated and affordable
  • Cooling problems are infrequent

Replacement may be worth considering if:

  • The system is older and inefficient
  • Repairs are frequent or costly
  • Cooling problems persist even after service

Understanding replacement costs and efficiency options can help you make a confident decision.

How to Prevent Cooling Problems in the Future

Many “AC running but not cooling” issues are preventable with regular care.

Best practices include:

Preventative maintenance helps extend system life and improves reliability—especially during peak cooling season.

Why San Antonio Homeowners Trust Stay Cool

At Stay Cool Air Conditioning & Heating, we believe in honest diagnostics, clear explanations, and old-fashioned service. When your AC isn’t cooling, we focus on finding the real issue—not upselling unnecessary repairs or replacements.

Our goal is to restore comfort quickly and help you make the best decision for your home and budget.

Need Help Getting Your AC Cooling Again?

If your AC is running but not cooling, don’t wait for the problem to get worse. Contact Stay Cool Air Conditioning & Heating to schedule a professional inspection and get your comfort back—fast, honest, and hassle-free.

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