7 reasons why your window air conditioner won’t start

With the intensifying heat outside, a window AC may be an essential part of your home. But what do you do when it won’t start? Thankfully, you don’t need to call in a expensive technician. Let’s walk through the troubleshooting steps so you can get your unit running smoothly.

If you find out that you need any replacement parts for your air conditioner while you’re troubleshooting, you can enter your model number at AppliancePartsPros.com to order them. Most orders arrive in just two business days, and we have thousands of free guides to show you how to install your new parts.

The troubleshooting information in this article is based on general service manuals and may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model.

Safety precautions

When working on any appliance, remember to keep safety first. Here are some tips to keep in mind: 

• Always power off and unplug your appliance or switch off the circuit breaker before you attempt any maintenance or replacement work. This keeps you safe by eliminating any risk of electric shock. 
• If the appliance has recently been used, give it plenty of time to cool down before working on it. 
• Take your time while working to prevent accidents and personal injuries. Rushing is the enemy of precision.
• Work in a well-lit area so you can see and access appliance parts.
• Keep your workspace free of clutter and other obstacles. Keep children and pets away from the work area.
• Never work on internal parts with wet hands. Make sure the work area is completely dry.
• Check the user manual to see if there are specific installation or safety instructions related to your appliance or replacement part. 
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause personal injury.
• Wear insulated work gloves to protect your hands from sharp metal parts and debris.
• When working with wires, avoid touching any exposed wires or terminals. If you need to touch a wire, use a non-conductive tool or wear insulating gloves to prevent electrical shock.
• Always take photos or make a note of wiring terminals or other connections before disconnecting them to make reassembly easier.
• Don’t test live voltage with a multimeter if you’re unfamiliar with how to prevent short-circuiting.

Why your window AC isn’t starting

Check out these common reasons that can prevent a window air conditioner from running and how you can fix them yourself.

Reason #1: Problem with the incoming power

1. Check the circuit breaker and reset it if it’s tripped.
2. Inspect the power cord for any breaks or damage. Replace it if it’s damaged.
3. Reseat the power cord plug in the outlet. Make sure the connection is secure.
4. Set a multimeter to continuity mode.
5. Use the meter probes to test the power cord for continuity. The meter should make a beeping sound if there’s continuity.

If the cord doesn’t have continuity or is damaged, replace it with a new one.

Reason #2: Faulty remote control

• Make sure the batteries in the remote control are new and installed correctly. If the remote isn’t working, try using the controls on the unit’s touchpad.
• Check that there’s nothing blocking the line of sight between the remote and the air conditioner.
• Replace the remote control if it’s malfunctioning.

Reason #3: Incorrect temperature setting

Check the temperature setting on the air conditioner. Lower the set temperature if it’s higher than the current room temperature.

Reason #4: Bad switch or thermostat

1. Refer to the diagram for your specific model to access the switch or thermostat.
2. Inspect the switch or thermostat terminals and wiring for any damage. If you find any damage, replace as needed.
3. If the unit has a switch, set a multimeter to continuity mode. If it has a thermostat, set the meter to resistance mode.
4. Use the multimeter probes to check the switch or thermostat, then compare the readings to the acceptable ones listed on the unit’s technical sheet.

If the switch or thermostat fails testing, replace them as needed.

Reason #5: Defective control panel or wiring

1. Refer to the model diagrams for your unit to access the control board and user interface. 
2. Inspect all the wires and connections at the control panel. Look for any obvious signs of damage, such as burns or frays. Reconnect any loose wiring. 
3. Inspect the control board for any burns or bulging.

Replace the wiring and/or control board if they’re damaged.

Reason #6: Faulty capacitor or start-relay switch

1. Check the terminals on the capacitor and start-relay switch for any damage or corrosion. 
2. Clean or replace the terminals as needed.
3. If the terminals look OK, discharge the capacitor.
4. Set a multimeter to continuity mode and use the probes to test the capacitor and start-relay switch.
5. Replace the capacitor or start relay switch if either fails testing.

Reason #7: Bad compressor

1. Inspect the compressor terminals for any evidence of burns or corrosion. Clean or replace them as needed.
2. Check the motor circuits for continuity using a multimeter.
3. Contact a certified technician to repair or replace the compressor, as they will need to handle the refrigerant properly.

Additional information

Thank you for reading! We hope this guide helped you get your air conditioner working again.

If you have any other appliance repair needs or projects, don’t hesitate to explore our other troubleshooting guides and videos. 

If you need replacement parts or some extra help with ordering them, grab your model number and head over to AppliancePartsPros.com, where you can chat with a pro, read our DIY blog and more.

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