AC not cooling

HVACUpdated March 2026

The answer to 'AC not cooling' is that there are several common causes, including a dirty air filter, low refrigerant levels, a problem with the compressor, or issues with the thermostat or electrical components. Symptoms can include the AC unit running constantly but not cooling the home effectively, warm air blowing from the vents, or the compressor not turning on.

For simple issues like a dirty air filter, you may be able to resolve the problem yourself by cleaning or replacing the filter. However, for more complex problems like low refrigerant or compressor issues, it's best to call a professional HVAC technician. They have the specialized tools and expertise to diagnose and repair the problem safely and effectively.

Sources

HVAC Experts— authority

Energy.gov— reference

This Old House— guide

Step-by-Step Guide

1
Replace the air filter
Locate and remove the air filter, then install a new one. Be sure to choose the correct size and type for your AC unit.
2
Check the thermostat settings
Ensure the thermostat is set to 'cool' and the temperature is set lower than the current room temperature.

Frequently Asked Questions

How often should I replace my air filter?

Most experts recommend replacing your air filter every 1-3 months, depending on factors like the size of your home and whether you have pets.

What should I do if my AC unit is not turning on at all?

If your AC unit is not turning on at all, there may be an issue with the electrical components or the thermostat. It's best to call a professional HVAC technician to diagnose and repair the problem.

How can I tell if my AC unit needs more refrigerant?

Signs that your AC unit needs more refrigerant include poor cooling performance, the compressor running constantly, and ice buildup on the coils. Only a professional HVAC technician should handle refrigerant refills.

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