If your window or wall air conditioner isn’t cooling properly, the most common reasons are a clogged air filter, dirty condenser coils, or a failed fan motor. These simple but critical issues can severely limit airflow and cooling performance, turning your living space into a sauna instead of a refuge from the heat. Understanding how to troubleshoot these problems, and when to test deeper components like the thermistor, can help you restore your AC’s cooling power without wasting money on unnecessary repairs. In this guide, you’ll learn how to inspect filters and coils, test electrical components, and identify when a thermistor replacement may be needed, ensuring your air conditioner works efficiently through the hottest months.
Check these 3 things first if your AC unit is not cooling properly
When troubleshooting a window or wall air conditioner that’s not cooling properly, you should check these three likely causes first:
1) Clogged air filter.
It’s the simplest thing to check, but one that can easily prevent your air conditioner from functioning the way you need it to. A clogged or dirty air filter will greatly reduce the cooling capacity of the AC by limiting the air flow through the unit. Window and wall air conditioner filters are designed to be easily removed. You can usually just detach the unit’s inlet cover to access and remove the filter. You can clean a dirty air filter by vacuuming off any heavy soil and running water through it, something you should consider doing monthly when the air conditioner is being used frequently. Does the filter appear damaged? Then you should replace the filter with a new one.
2) Dirty condenser coils.
Dust and dirt will build up on the inside (the fan side) of the air conditioner’s condenser coils which can prevent the AC unit from cooling properly. The coils can be cleaned by blowing compressed air through them or by using a soft bristle brush and a spray bottle of household cleaner to wipe the dirt off. You can also use a dedicated HVAC condenser coil cleaner such as Triple-D Universal Coil Cleaner. You’ll need to completely remove the air conditioner cabinet to access the coils and we recommend doing this cleaning outdoors as it can get messy.
3) Failed fan motor.
If you can hear the air conditioning unit running, but the air doesn’t seem to be recirculating, it’s likely the fan motor has burned out. You should first confirm that the fan blades or blower wheel are unobstructed by debris. Next, you can use a multimeter to test the fan motor for electrical continuity. You should also consider testing the unit’s run capacitor to confirm it can store and release the proper electrical charge to run the fan motor (keep in mind, a faulty run capacitor will likely not be able to provide a sufficient charge to the unit’s compressor either, so you probably won’t hear the AC running at all).
Testing the air conditioner’s thermistor
The air conditioner repair help you need from Repair Clinic
Need some assistance in locating and uninstalling a window or wall air conditioner’s thermistor? Repair Clinic’s “Video & Articles” library has the repair help you need. Enter the unit’s full model number in the search bar to find model-specific diagrams identifying the location of every part as well as step-by-step guides and videos showing how to replace those parts, such as this one taking you through replacing a condenser and outdoor air thermistor on an LG Air Conditioner (Model LW2217IVSM), or this video demonstrating the correct way to install a new fan motor on a Frigidaire Air Conditioner (Model FFTA0833U10).
Find genuine OEM air conditioner parts from Repair Clinic
Repair Clinic also makes it easy to find the right thermistor, fan motor, fan blade, blower wheel, run capacitor, or air filter that matches the specific unit you need to repair. Just enter the full model number of the air conditioner in the Repair Clinic website search bar to see a complete list of the genuine OEM parts compatible with your model, from top manufacturers like Admiral, Bryant, Carrier, Frigidaire, GE, Goldstar, Goodman, LG, Lennox, Payne, Rheem, and WeatherKing. You can narrow that list down using the “Part Category” filter (example: “Sensor & Thermistor”) followed by the “Part Title” filter (example: “Thermistor”) to locate the exact part you’re looking for. By providing you with quality replacement parts plus the know-how to fix the AC unit yourself, Repair Clinic is a valuable repair partner.