If your air conditioner is running but not cooling your home, the most common causes are a dirty air filter restricting airflow, low refrigerant from a leak, a dirty condenser coil, a thermostat set incorrectly, or a frozen evaporator coil. In North Texas, where outdoor temperatures regularly exceed 100°F in summer, an AC that’s losing cooling power should be diagnosed quickly, since the strain of extreme heat tends to turn a small issue into a full system failure.
Most Common Causes of an AC Not Cooling
1. Dirty or Clogged Air Filter
A clogged air filter restricts airflow across the evaporator coil, reducing the system’s ability to cool air and pushing the whole unit to work harder. This is the single most common (and easiest to fix) cause of poor cooling performance. Filters should generally be checked monthly and replaced every 1–3 months during peak summer use.
2. Low Refrigerant (Leak)
Refrigerant absorbs heat from indoor air and releases it outside. If the system is low on refrigerant due to a leak, it can’t absorb enough heat, resulting in warm air blowing from the vents. Low refrigerant is not something that gets “used up” like fuel, if a system is low, it almost always means there’s a leak that needs to be located and repaired.
3. Dirty Condenser Coil
The outdoor condenser unit releases heat pulled from inside the home. When the coil is covered in dirt, pollen, or debris, it can’t release heat efficiently, which reduces cooling capacity, sometimes significantly, especially during peak summer heat.
4. Frozen Evaporator Coil
Ironically, one of the most common reasons for warm air is a frozen coil, usually caused by restricted airflow (dirty filter) or low refrigerant. Once ice builds up on the coil, it blocks airflow entirely, and the system may need to be shut off to thaw before a technician can diagnose the underlying cause.
5. Thermostat Issues
Incorrect settings, dead batteries, or a miscalibrated thermostat can all cause an AC to run without actually cooling to the desired temperature. This is worth ruling out first since it’s the fastest and cheapest fix.
6. Undersized or Aging System
A system that’s too small for the home, or one nearing the end of its 12–15 year lifespan, may struggle to keep up during extreme heat even when running properly.
Quick Checks Before Calling a Technician
- Check and replace the air filter if it’s dirty
- Confirm the thermostat is set to “cool” and the temperature is below room temperature
- Check the outdoor unit for visible debris, leaves, or overgrown vegetation blocking airflow
- Check if the vents are open and unblocked throughout the house
- Check the circuit breaker if the system isn’t turning on at all
When to Call an HVAC Technician
Call a licensed HVAC technician if:
- The air filter is clean but the AC still isn’t cooling
- You notice ice on the indoor coil or refrigerant lines
- You hear unusual noises (grinding, hissing, or clicking)
- The system is short-cycling (turning on and off frequently)
- You suspect a refrigerant leak (refrigerant should never need regular “topping off”)
- The unit is more than 12–15 years old and cooling performance has been declining
How Often Should HVAC Systems Be Serviced?
Most manufacturers and HVAC professionals recommend a maintenance check twice a year, once before summer and once before winter, to catch small issues (like low refrigerant, worn parts, or dirty coils) before they cause a full breakdown during peak-demand months.
Frequently Asked Questions
Why is my air conditioner running but not cooling the house?
The most common causes are a dirty air filter, low refrigerant from a leak, a dirty outdoor condenser coil, or a frozen evaporator coil. Checking the filter and thermostat settings first can rule out the simplest causes.
Is it normal for an AC to need refrigerant added every year?
No. Refrigerant operates in a closed loop and isn’t consumed during normal operation. If refrigerant needs to be added regularly, it indicates a leak that should be located and repaired.
How long does an AC unit typically last?
Most central air conditioning systems last 12 to 15 years with regular maintenance, though this can vary based on usage, maintenance history, and system size relative to the home.
Why does my AC freeze up in the summer?
A frozen coil is typically caused by restricted airflow (often a dirty filter) or low refrigerant. Running the system with a frozen coil can damage the compressor, so it should be turned off until the issue is diagnosed.
Does Capital Plumbing offer HVAC repair in the DFW area?
Yes. Capital Plumbing, Inc. provides air conditioning repair, installation, and maintenance throughout Pilot Point, TX and the greater DFW metroplex. Call (940) 440-1100 to schedule service.
Capital Plumbing, Inc. (TACLA96144C) provides HVAC installation, repair, and maintenance services across Pilot Point, TX and the DFW metroplex, alongside licensed plumbing and gas line services.