Window Air Con Not Turning On? Diagnose & Fix It Today

I’m sure you’ve heard of Murphy’s Law. The law says that anything that can go wrong will go wrong. Let’s add to that — it’ll go wrong at the worst time. Like it’s a steaming hot day and your window air conditioner is not turning on.

Before you pull out your credit card and hit your favorite appliance website, there are a few things you can do to diagnose and fix your AC.

Window air conditioners may not turn on because of various reasons, including blown fuses or tripped breakers, dirty coils, refrigerant leaks, a dead capacitor, dirty filters, and more. With the exception of a refrigerant leak, you may be able to fix the problem yourself.

This article will take you through all the reasons why your window air conditioner may not start up, and possible fixes. So keep reading.

What You’ll Need

Depending on what the problem is with your air conditioner, you will need different tools. But if your air conditioner isn’t turning on, it might be a good idea to go through each step below and do whatever cleaning or testing is recommended.

Here are the tools you’ll need.

  • Screwdriver
  • Garden hose
  • Coil brush
  • Fin tool
  • Coil cleaner – alternatively, you can use dish soap and warm water
  • Multimeter
  • Vacuum or hand broom

What to do When Your Window Air Conditioner Won’t Turn On…

Now, let’s start off with the most obvious. 

… Check & Fix Your Power Source

This is a no brainer, but your AC won’t run if it’s not getting power, right? And just because you have it plugged in doesn’t mean electricity is getting to the unit. 

outlet with plug
The first step is to test another outlet

If you have another outlet close by, try plugging your unit into that and see if it works. If it does, yay. You know you have a power source problem at the original outlet. If not, try the following. 

Step 1

Examine the power cord for any obvious damage. Scorch marks, pet bite marks—if they’re human, you have a bigger problem!—anything that would cause the wire to short. 

If the cord is frayed or chewed, it can be replaced. If the cord is burnt, you need to find the source of the burn. 

Step 2

If there is no visible damage to the cord, check the breaker or fuse your outlet is attached to. If the breaker is tripped, reset it. If the fuse is blown, replace it. 

However, if you’re resetting or replacing a breaker or fuse often, there’s a problem somewhere that must be addressed, because a constantly tripping breaker is a fire hazard. 

If there’s no problem with your power source, keep investigating. 

…Check & Replace the Remote-Control Batteries 

Does your window air conditioner operate using a remote control?

Step 1

Test the remote. Does the air conditioner beep when you send a command? Test and replace the batteries as necessary

…Check & Change Your Filter

Despite manufacturers repeatedly telling consumers they need to keep up with filter maintenance, this is one of the most neglected steps. And hand-in-hand with that, it’s one of the most common causes of air conditioner problems.

A lack of airflow will stop your air conditioner from working. It can get so bad that your coils will freeze over and as a result, your air conditioner won’t turn on.

If this is you, the fix is simple.

Step 1

Turn off your air conditioner

Step 2

Following the manufacturer’s guidelines, remove the front grill

Step 3

Remove and replace the filter, making sure your new filter follows the manufacturer’s specifications

Step 4

Reassemble your air conditioner

Step 5

Moving forward, follow the manufacturers filter replacement guidelines — typically every month during the cooling season

…Check & Replace Your Capacitor

How to Replace a Window Air Conditioner Capacitor

The capacitor holds a temporary store of energy and gives your air conditioner the extra boost it needs to power up. If it’s dead, your air conditioner won’t turn on.

Since you can get a significant shock from any leftover, high-voltage energy in the capacitor, handling it is potentially dangerous. If you’re uncomfortable with the following step, have a handyman, electrician, or appliance repair technician deal with the situation.

If you’re confident in being able to DIY, follow the steps below. Note that the capacitor is a round, tube-shaped part, typically black or silver metal.

Step 1

Unplug your air conditioner and remove it from the window

Step 2

Set your air conditioner on a level, sturdy surface

Step 3

Remove the front grill, the filter, and the entire cabinet.

Step 4

Discharge the capacitor, carefully following the steps in the video below. This is critical, so please watch the tutorial.

How to Discharge a Capacitor

Step 5

Before doing anything else, take a picture of your capacitor’s wiring so you’ll remember how to reconnect them.

Step 6

Visually inspect the capacitor for damage— is it leaking, bulging, or somehow deformed?

Step 7

Assuming there’s no visible damage—which makes testing irrelevant since you’ll need to replace it anyway, use a multimeter to test the capacitor 

Step 8

Using the multimeter’s capacitor setting, touch each red and black probe to each of the capacitor’s terminals and check the reading against the listed rating for your capacitor

Step 9

The capacitor needs to be replaced if the reading and rating don’t match or if it’s visibly damaged

…Check & Clean Your Compressor 

Without the compressor, your air conditioner won’t work. Literally. 

It’s the compressor’s job to move the refrigerant through the unit, changing it from a liquid form to a gas form, and back again. If that cycle stops, the condenser coils can freeze over, which not only makes it impossible for your AC to cool enough, it can make it inoperable. 

Cleaning the condenser coils should be part of your annual maintenance plan. If you keep up with that you won’t have to worry about them freezing up and shutting down your air conditioner.

Here are the steps.

Step 1

Unplug and remove your air conditioner from the window 

Step 2

Take it outside and set it on a flat, stable surface

Step 3

Remove the front grill, filter, and cabinet, following the manufacturer’s guidelines

Step 4 

Refer to your manual for the placement of your condenser coil

Step 5 

Remove any large debris from the coils by hand, and then use a brush or vacuum to remove any loose dust and dirt. They aren’t necessary, but you can also buy a coil brush that’s specifically made for this purpose.

Step 6

Inspect the fins over the coils and if any are bent, use a fin tool to straighten them out

Step 7

With your garden hose set to low pressure, rinse off the coils

Step 8

To clean the coils, you have the option of using coil cleaner or simply using mild soap and warm water in a spray bottle.

If you do opt for coil cleaner, determine if your coils are copper or aluminum and purchase a brand that will work with what you have. Spray a layer of the cleaner over the coils and as it foams it will lift off any surface grime.

Step 9 

Let the foam sit for the manufacturer’s recommended amount of time 

Step 10

Assuming you’ve purchased the type of form that needs to be rinsed off, do so using a low-pressure garden hose. However, some types do not require rinsing.

Step 11

Depending on weather conditions, allow your air conditioner to sit outside for enough time to completely air dry

Step 12

Reassemble and reinstall your air conditioner 

…Check & Clean Drain Pan

Not all window air conditioners have a drain hole and plug, but they all have a condensate drain pan. And if the pan gets clogged up, the water can cause the condenser to freeze over or trigger a float switch that will shut the system down as a safety measure. 

So you need to drain and clean the pan.

Step 1

First, check the bottom and lower sides of the exterior part of the unit for a drain plug. If you find one, remove it and allow the water in the pan to drain out.

Step 2

If nothing drains out or if you find no plug, remove the air conditioner from the window and sit down somewhere flat in stable

Step 3

Remove the front grill, the filter, and then the entire cabinet

Step 4

Remove the screws that hold the drain pan in place and then remove any dirt and debris from the bottom of the pan. If you took your air conditioner outside to clean, use a garden hose on a low-pressure setting to clean out the pan.

Step 5

Reassemble and reinstall your air conditioner, making sure to preserve the slight downward tilt — if the manufacturer requires it

When Your Window Air Conditioner Won’t Turn On… Maybe it’s Dead

Window air conditioners have a lifespan of about 8 to 10 years

However, if you’ve been running into problems like any of the above, it could be that your air conditioner hasn’t been properly maintained. If that’s the case, lack of maintenance does impact the quality and life of your unit, so it’s possible for it to die well before its expected lifespan.

It may be time to consider buying a new window air conditioner.


There are a number of things that can go wrong with an air conditioner — often because of a lack of proper maintenance — that can shut it down and stop it from restarting.

However, doing any of the following may get it going again.

Unfortunately, it could also be that your air conditioner is dead and it’s time to consider buying a new one.

Hopefully, we’ve provided sufficient information to help you diagnose and fix the problem with your air conditioner. While you’re here, why not check out the related posts below? Perhaps there’s something else we can help you with.

I've been helping homeowners with appliance repair since 2016. Starting out as an enthusiastic amateur, I've since worked with many Appliance, HVAC, and DIY experts over the last 7+ years. My mission is to help fix your appliances and prevent future issues - saving you stress, time, and money. Visit my author page to learn more! Read more