Air conditioners usually fail for a few repeatable reasons—restricted airflow, dirty coils, thermostat/control issues, low refrigerant, or blocked drainage—so most “AC not cooling” complaints can be narrowed down quickly with a simple checklist. Dirty filters/coils and incorrect refrigerant charge are also common efficiency killers that make the system run longer and cost more to operate. ​ 5 common AC problems 1) AC not cooling (clogged air filter) Typical signs Weak airflow from vents / indoor unit and slow cooling. ​ Ice/frost on the indoor coil in some cases (because airflow gets restricted). ​ Why it happens A clogged/dirty filter restricts airflow, reducing the AC’s ability to move warm air across the coil and deliver cool air effectively. ​ Restricted airflow can contribute to frozen components (like the evaporator coil). ​ How to fix (DIY) Turn the unit off, remove the filter, clean it (if washable) or replace it, then run the AC again. ​ Keep return vents unblocked so airflow stays steady (basic airflow issues can trigger bigger problems). ​ When to call a technician If cooling doesn’t improve after a filter clean/replace, the issue may be coil dirt, refrigerant level, or a failing part. ​ 2) AC running but still warm (dirty condenser coil) Typical signs The AC runs longer than usual and struggles to remove heat. ​ Outdoor unit looks dusty or blocked by leaves/debris. ​ Why it happens The condenser coil (outdoor) must reject heat; dirt/leaves/debris reduce heat transfer, forcing the AC to work harder and cool worse. ​ Dirty coils reduce the system’s ability to cool and can increase energy costs while shortening equipment life. ​ How to fix (DIY) Switch off power, gently clear leaves and debris around the outdoor unit, and keep some open space for airflow. ​ Light cleaning may help, but deep coil cleaning should be done carefully to avoid damage. ​ When to call a technician If the coil is heavily clogged or fins are bent, professional cleaning is safer and more effective. ​ 3) Water leaking from indoor unit (clogged condensate drain) Typical signs Water dripping from the indoor unit or damp patches near it. ​ In some systems, a clogged drain can cause shutdowns or humidity problems. ​ Why it happens The evaporator coil removes moisture from air, creating condensate that should flow out through a drain line. ​ Mold/algae/debris can build up and block the drain, potentially causing overflow and water damage. ​ How to fix (DIY) Locate the drain access and flush the drain line; common home methods include distilled white vinegar, hot water, or hydrogen peroxide as a cleaning solution. ​ If safe and accessible, ensure the drain outlet isn’t physically blocked. ​ When to call a technician If leaks persist or you see repeated clogging, a professional should clear and inspect the drain system to prevent damage and recurring humidity issues. ​ 4) Frozen evaporator coil (ice on indoor coil) Typical signs Visible ice on the indoor coil/lines and reduced cooling. ​ Water leakage after the ice melts. ​ Why it happens Insufficient airflow (often from dirty filters) can lead to freezing. ​ Low refrigerant can also cause the evaporator coil to freeze. ​ How to fix (DIY) Turn off cooling (or turn the system off) to let the ice melt, then clean/replace the air filter and check airflow. ​ If freezing returns quickly, avoid repeated run cycles until the root cause is fixed. ​ When to call a technician If low refrigerant is suspected, professional diagnosis is needed (refrigerant issues aren’t a safe DIY fix). ​ 5) Hissing sound / oily residue / poor cooling (refrigerant leak or low refrigerant) Typical signs Reduced cooling performance because the system can’t operate efficiently at low charge. ​ Possible hissing sound near the indoor/outdoor coil areas and/or oily residue around components. ​ Why it happens A leak causes low refrigerant levels (low charge), which lowers efficiency and cooling capacity. ​ Too much or too little refrigerant makes the system less efficient and can reduce equipment life. ​ How to fix Refrigerant leak testing, repair, evacuation, and correct recharging should be done by a trained HVAC professional. ​ When to call a technician (immediately) If you suspect a leak (hissing/oily residue), stop running the unit and schedule service. ​ Quick troubleshooting checklist Use this order to avoid wasting time: Check thermostat settings (mode = Cool, temperature set lower than room temperature) before opening the unit. Check/clean the air filter first because restricted airflow is a frequent cause of weak cooling and icing. ​ Inspect the outdoor unit area for debris buildup that can reduce heat transfer. ​ If there’s water leakage, check the drain line for blockage and flush it. ​ If ice is present, thaw first, then address airflow and get refrigerant checked if freezing repeats. ​ Preventive maintenance Simple habits prevent most breakdowns: Change/clean filters regularly to avoid airflow restriction and performance loss. ​ Clean evaporator and condenser coils because dirty coils reduce cooling ability and increase energy costs. ​ Inspect the condensate drain; a plugged drain can cause water damage and affect indoor humidity. ​ Get refrigerant levels checked during routine service because incorrect charge reduces efficiency and can shorten equipment life. ​ When to call a technician Book professional service if any of the following happens: Suspected refrigerant leak (hissing sound, oily residue, or persistent low cooling). ​ Repeated coil freezing after filter cleaning and airflow checks. ​ Ongoing water leakage or repeated drain clogs (to prevent water damage and mold issues). ​ FAQ Why is my AC running but not cooling? Common causes include a clogged air filter, dirty condenser coils, or low/incorrect refrigerant charge. ​ Can a dirty filter really cause an AC to freeze? Yes—restricted airflow from a dirty filter can contribute to ice buildup and a frozen evaporator coil. ​ Is water dripping from the indoor unit serious? It can be, because blocked condensate drains may lead to overflow, humidity issues, and even water damage if ignored. ​