Window Air Conditioner Troubleshooting Guide
**SAFETY NOTE**
Only you can assess your ability to perform these tasks. This is a guide and cannot provide details for every specific situation. Always unplug the unit before inspecting internal wiring or mechanical components.
From the repairman's point of view, troubleshooting starts with the basics. Following this checklist can help you identify common issues and potentially save you over $100 on a service call.
Diagnostic & Repair Checklist
- 1. Clean Filter & Coils: Ensure airflow is not blocked by a dirty filter or debris on the evaporator/condenser coils.
- 2. Verify Power Supply: Check the home breaker or fuse (typically 15A or 20A circuit). Verify it is properly sized.
- 3. Reset Current Interrupter: Push the reset button on the power cord's interrupter plug to ensure the unit is receiving power.
- 4. Inspect Internal Wiring: If the breaker trips again, check for burnt or loose connections inside the unit.
- 5. Test Capacitors: If the unit has power but the fan or compressor won't start, check the run capacitors.
- 6. Check Fan Operation: Ensure fan blades spin freely. If the motor fails but the capacitor is good, check the fan motor and switch.
- 7. Monitor Compressor Temp: If the compressor won't start and feels hot to the touch, allow it to cool and check resistance.
- 8. Listen for "Clicking": A click sound indicates the unit is trying to start the cooling cycle but may have a faulty starting component.
- 9. Test Thermostat/Sensor: Check thermostat settings or test the electronic sensor for proper resistance values.
- 10. Measure Temp Drop: Check the air entering vs leaving the unit; look for a 10 to 15 degree difference.
Repair or Replace?
Generally, if a compressor is bad on a window air conditioner, it is more cost-effective to replace the entire unit than to pay for a professional repair. If your unit starts but fails to cool effectively (and has clean coils), it may be low on refrigerant—a sign that replacement is likely needed.
Before buying a new unit, check our reliability rankings to see which brands last the longest in the field.
View 2026 Window AC Ratings →Troubleshooting FAQs
Is it worth fixing a bad compressor in a window AC?
Generally, if the compressor is bad on a window air conditioner, it is cheaper to replace the entire unit than to pay for a professional repair.
What is the normal temperature drop for a window AC?
You should check the difference between the air entering and leaving the unit; there should typically be a 10 to 15 degree difference during a complete cooling cycle.
What should I check first if my window AC won't turn on?
Check the power supply, including the breaker or fuse and the current interrupter on the power cord. Ensure the reset button on the cord has been pushed.
Identify the Failing Component
If your troubleshooting has led you to a specific part, use these expert guides to test and replace the component safely:
Capacitors
The #1 failure in HVAC. Learn to safely discharge and test Microfarads (MFD) in your outdoor unit.
Test Capacitors →Compressor
The heart of your ductless system. Learn how to identify mechanical failure versus electrical issues.
Diagnose Compressor →Refrigerant Levels
Low charge causes icing and high bills. Understand how to check for leaks and proper levels.
Check Charge →
Meet the Expert: HVAC Repair Guy (Richard Reed)
HVAC Specialist & Founder of HVAC For Beginners
Richard Reed (known to his followers as the HVAC Repair Guy) brings over 17 years of specialized HVAC industry experience. His unique background includes serving as an electrician in nuclear power before completing a 4‑year HVAC service apprenticeship and 8 years of field experience. Based in the Midwest, he has helped homeowners understand, maintain, and upgrade their systems since the early 2000s. His mission is to provide unbiased, “repairman’s point of view” insights into energy conservation and alternative energy solutions.