Why is my AC running but not cooling to temperature?
In short, the unit may be operating but not delivering cold air because of airflow restrictions, refrigerant or coil problems, or a failing cooling component. Some fixes are simple, while others require a licensed HVAC professional.
When an air conditioner runs without reaching the desired temperature, it usually points to an issue with heat transfer, airflow, or the system’s controls. Below is a guided look at common causes, safe do-it-yourself checks, and guidance on when to call for professional service.
Common causes where the problem usually lies
Airflow problems
Airflow is essential for cooling. If the system cannot move enough air across the evaporator or into living spaces, you’ll feel weak or no cooling even though the compressor is running.
- Clogged or dirty air filters restricting airflow.
Addressing airflow issues often improves cooling quickly. If problems persist after checking filters, vents, and exterior coils, a professional should assess ductwork and airflow balance.
Refrigerant and cooling cycle problems
Problems with the refrigerant charge or the cooling cycle prevent heat transfer from indoors to outdoors, leading to insufficient cooling.
- Low refrigerant due to a leak in the copper lines or coil—this requires a licensed technician to repair and recharge.
refrigerant-related issues are not DIY fixes; refrigerant handling and charging require certification and can be hazardous.
Electrical and thermostat issues
Electrical faults or misreadings from the thermostat can cause the system to run without effective cooling or cycle oddly.
- Failed capacitors, contactors, or other components in the outdoor unit or air handler.
Electrical or sensor problems often require diagnostic equipment and expertise; avoid tampering with high-voltage components.
Do-it-yourself checks you can safely perform
These basic checks help you identify simple, fixable causes and decide whether a professional is needed. Always turn off power before inspecting electrical components or touching wiring.
- Check thermostat settings to ensure cooling mode is on, with a reasonable setpoint and fan set to auto or on.
- Replace or clean disposable or reusable filters; dirty filters block airflow and reduce cooling efficiency.
- Inspect the outdoor condenser area and remove leaves, grass, and debris; ensure at least 2 feet of clearance on all sides.
- Check indoor supply and return vents for blockages and verify the blower is delivering air (you should feel air from registers).
- Look for frosting or ice on the indoor evaporator coil; if icing occurs, turn off the system to thaw and have it inspected if it recurs.
- Listen for unusual noises or burning smells from the outdoor unit or air handler; stop and contact a professional if you notice anything concerning.
If these checks don’t restore cooling, or you notice repeated icing, unusual noises, or electrical smells, seek professional diagnosis promptly to prevent further damage.
When to call a professional
Certain problems require a licensed HVAC technician, especially refrigerant handling, electrical work, and system diagnosis beyond basic maintenance.
- Suspected refrigerant leaks or the need for a refrigerant recharge.
- Electrical diagnostics, capacitor/contactor replacement, or wiring repairs.
- Compressor assessment, lubrication checks, and confirmation of proper operation.
- Condenser coil cleaning, duct inspection, and verifying proper airflow balance.
- Thermostat sensor calibration, compatibility checks, or replacement.
Expect a technician to assess refrigerant health, test electrical components, and check for airflow and duct integrity. Obtain a written estimate and discuss warranties or service guarantees before proceeding.
Summary
Most cases of running but not cooling fall into airflow issues, refrigerant or coil problems, and electrical or thermostat faults. Start with simple steps like replacing filters, clearing outdoor coils, and verifying thermostat settings. If the problem persists or involves refrigerant leaks, ice buildup, or electrical components, call a licensed HVAC professional for a thorough diagnostic and safe repair.
How long should it take to cool a house from 80 to 72?
It should take a properly functioning air conditioner approximately 3 hours to cool a moderate-sized house from 80∘F80 raised to the composed with power cap F80∘𝐹 to 72∘F72 raised to the composed with power cap F72∘𝐹, though this can vary based on the system's size, insulation, humidity, and outside temperature. A good general rule of thumb is that a central AC unit can cool a home by about 1 degree Fahrenheit per hour under normal conditions.
Factors that can affect cooling time
- Size of the AC unit: A unit that is too small for the house will take longer to cool it down.
- House size and insulation: Larger homes with poor insulation will take longer to cool.
- Outside temperature and humidity: High outdoor temperatures and humidity will increase the time it takes to cool the inside.
- AC maintenance: Dirty air filters, clogged condensate drains, or dirty coils can all reduce efficiency.
- Air leaks: Leaky ducts or windows allow warm air to enter the house, slowing down the cooling process.
Tips to speed up cooling
- Close blinds and curtains: This will help block the sun's heat from entering the house.
- Change your air filter: A clean filter ensures proper airflow through the system.
- Reduce internal heat: Turn off unnecessary lights and appliances that generate heat.
What should my AC be set at if it's 100 degrees outside?
- Although the temperature outside may be near 100 degrees, experts say you should be using what they call the 20-degree rule. That means you should keep your thermostat at 80 degrees when it's 100 degrees outside.
Why is my AC running but not cooling to set temperature?
One common reason is a dirty or clogged air filter, which restricts airflow and reduces the system's efficiency. Low refrigerant levels can also cause the AC to struggle in reaching the desired temperature, as it affects the cooling process.
Why is my AC set to 72 but reads 78?
A thermostat resetting to 78°F often indicates a faulty internal memory or wiring issue. First, check the thermostat's batteries and replace if low. Inspect wiring connections for looseness or corrosion, especially the R (power) and W (heat) terminals.
