Why is my AC Not Cooling?

When your air conditioner stops cooling during a Katy summer, it's more than uncomfortable- it's urgent. With Texas heat and humidity, your AC system works hard almost year-round. If your AC is running but not cooling your home properly, there are several common causes that homeowners experience. 

 

Below, the experts at GRB Mechanical explain the most frequent reasons your AC may not be cooling- and when it's time to call for professional AC repair. 

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1. Dirty Air Filter

One of the most common causes of AC not cooling is a clogged air filter. When airflow is restricted your system struggles to circulate cool air, ice can form on the evaporator coil, energy bills increase and cooling performance drops. We recommend checking your filter monthly during peak Summer months.

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2. Low Refrigerant Levels

If your AC is blowing warm or slightly cool air, low refrigerant may be the issue. Signs include warm air from vents, ice on refrigerant lines, hissing or bubbling sounds and longer cooling cycles. Low refrigerant typically means there is a leak. This requires professional AC repair- simply "topping it off" is not a long-term solution. 

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3. Frozen Evaporator Coil

When airflow is restricted or refrigerant is low, your evaporator coil can freeze. You may notice ice buildup on indoor components, AC running constantly and little to no airflow from vents. If you see ice, turn off your system, allow to thaw and call your AC professional.

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4. Clogged Condensate Drain Line

In humid areas like Houston, condensate drain lines frequently clog. When this happens, the system may shut off, water can back up into the unit and you may see water around your indoor system components. Routine maintenance prevents this common issue.

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5. Thermostat Problems

Sometimes the issue isn't your AC system- it's your thermostat. Check: Is it set to "Cool"? Are the batteries dead? Is it calibrated properly? Is it located near a heat source? Upgrading to a programmable, smart thermostat can improve efficiency and performance. 

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6. Dirty Outdoor Condenser Unit

Your outdoor unit releases heat from your home. If it's covered in dirt, grass or debris, it can't function properly. Common signs of this are your AC running constantly, struggling to keep up with afternoon heat, and higher electricity bills. Keeping at least two feet of clearance around the condenser helps maintain performance. 

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7. Failing Compressor

The compressor is the heart of your AC system. If it's failing, your system may run cool but not effectively. Warning signs include loud clicking or grinding noises, AC not starting consistently or your breaker tripping frequently. Compressor issues require immediate attention and professional evaluation. 

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If your AC is not cooling, don't wait until the Texas heat makes it unbearable. GRB Mechanical provides fast, honest and professional AC repairs in Katy TX and the surrounding Houston area. We diagnose problems accurately and recommend practical solutions- whether it's a simple fix or a more involved repair. 

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GRB Mechanical, February 2026

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