There’s nothing more disappointing than expecting a blast of cool air from your AC on a hot summer day, only to find that the fan is blowing, but the air isn’t cold. This common issue can leave you feeling uncomfortable and frustrated, especially when you can’t seem to pinpoint the problem.
We’ll go through some reasons why your AC fan might be blowing without producing cold air. We’ll explore how to determine if your AC is low on refrigerant, the signs of a refrigerant leak, and how to properly check if your AC is cooling as it should. Additionally, we’ll discuss why your AC may not be able to cool your space below 75 degrees.
By understanding these potential issues, you’ll be better prepared to diagnose the problem and take the appropriate steps to get your AC back to blowing cold air, ensuring your comfort throughout the warm summer months.
How to know if the refrigerant is low?
- Warm air blowing from vents – If the air coming out of your AC vents feels warm or not as cold as it should be, this could indicate low refrigerant levels. The AC is unable to properly cool the air due to insufficient refrigerant.
- Reduced cooling performance – If your AC is running constantly but not adequately cooling your home, or it’s taking much longer than usual to reach the set temperature, low refrigerant may be the culprit.
- Frozen evaporator coil – When refrigerant is low, it causes the evaporator coil to become extremely cold, leading to ice buildup on the coil itself and the refrigerant lines. If you notice ice or frost on these components, it’s likely due to a refrigerant issue.
- Hissing or bubbling sounds – A hissing noise can indicate a refrigerant leak as the gas escapes, while a bubbling sound may mean liquid refrigerant is leaking out. These unusual noises coming from your AC unit often point to low refrigerant levels.
- Higher electric bills – An AC low on refrigerant has to work harder and run longer to cool your home, leading to increased energy usage and higher utility bills compared to normal.
To confirm low refrigerant levels, an HVAC technician can connect gauges to your AC system to measure the actual refrigerant pressure. If the pressure is below the manufacturer’s specifications, a refrigerant recharge is needed.
It’s important to note that refrigerant doesn’t get “used up” – the only way levels get low is if there is a leak in the system. An AC professional should identify and repair any leaks before recharging the refrigerant to the proper level.
How can I tell if my AC is leaking refrigerant?
- Warm air blowing from vents – If the air coming out of your AC vents feels warm or not as cold as it should be, this could indicate a refrigerant leak. The AC is unable to properly cool the air due to insufficient refrigerant.
- Reduced cooling performance – If your AC is running constantly but not adequately cooling your home, or it’s taking much longer than usual to reach the set temperature, a refrigerant leak may be the culprit.
- Frozen evaporator coil – When refrigerant is low, it causes the evaporator coil to become extremely cold, leading to ice buildup on the coil itself and the refrigerant lines. If you notice ice or frost on these components, it’s likely due to a refrigerant leak.
- Hissing or bubbling sounds – A hissing noise can indicate a refrigerant leak as the gas escapes, while a bubbling sound may mean liquid refrigerant is leaking out. These unusual noises coming from your AC unit often point to low refrigerant levels caused by a leak.
- Higher electric bills – An AC low on refrigerant has to work harder and run longer to cool your home, leading to increased energy usage and higher utility bills compared to normal.
How to check if AC is cooling properly?
- Run the AC for at least 15-20 minutes before testing to allow it to reach steady state operation.5
- Check the temperature of the air coming out of the supply vents using a thermometer. Hold the thermometer in the airflow for at least 5 minutes to get an accurate reading.
- Check the temperature of the air going into the return vents using a thermometer. Again, allow at least 5 minutes for an accurate measurement.
- Calculate the temperature difference between the supply and return air. Subtract the supply air temperature from the return air temperature.
- If your AC is working properly, there should be a 15-20°F temperature difference between the supply and return air. HVAC professionals call this the “evaporator Delta T”.
- If the temperature difference is less than 15°F, your AC may be low on refrigerant, have weak compressor valves, leaking valves, or leaking ductwork. An HVAC technician should diagnose the issue.
- If the temperature difference is more than 20°F, your AC likely has restricted airflow due to dirty air filters, wrong blower speed setting, dirty evaporator coil, or undersized ductwork. Try replacing the air filter first.
Some additional things to check:
- Make sure the outdoor condenser unit is running and not blocked by debris
- Check that all supply vents are open and unobstructed
- Ensure the thermostat is set to “cool” mode and the desired temperature
If you’ve gone through these steps and your AC still isn’t cooling properly, it’s best to contact an HVAC professional to diagnose and repair the system. Attempting to fix issues like refrigerant leaks yourself can be dangerous.
Why is my AC not cooling below 75?
- Low refrigerant – If your AC system is low on refrigerant due to a leak or undercharging during installation, it won’t be able to cool effectively. An HVAC technician needs to locate and repair any leaks, then recharge the system to the proper level.
- Dirty air filter – A clogged air filter restricts airflow through your AC system, reducing its cooling capacity. Check your filter monthly and replace it when dirty, generally every 1-3 months.
- Blocked or closed vents – Make sure all your supply vents are open and unobstructed by furniture, curtains, or debris. Closed or blocked vents reduce airflow and cooling power.
- Undersized AC unit – If your air conditioner is too small for the space it’s trying to cool, it will struggle to lower the temperature sufficiently, especially on very hot days. Proper sizing is key for effective cooling.
- Dirty evaporator or condenser coils – If the evaporator coil inside or the condenser coil outside becomes dirty, heat transfer is impeded and cooling performance drops. Annual professional maintenance is recommended to clean the coils.
- Thermostat issues – Make sure your thermostat is set to “cool” mode and the desired temperature. If it’s not properly calibrated, the actual room temperature may not match the set temperature.
- Leaky ductwork – If your ductwork has leaks, tears, or poor insulation, the cooled air can escape before reaching the intended rooms. An HVAC professional can test your ducts and seal any leaks.
In general, if your AC can’t keep up on very hot days, it may only be able to cool your home about 15-20°F below the outside temperature. However, if your AC consistently fails to reach the desired temperature, it’s best to have an HVAC technician inspect, diagnose, and repair your cooling system.