How To Recharge A Window AC

Last Updated on May 4, 2021 by Kimberly Crawford

There will come a time when you window AC would not be as performing as before. It would spit less cooler air and the water leak by the condenser would make more water pooling outside the room. When this happens, it might be because refrigerant has lost that substance that makes it emit cool air. The one solution to that is to recharge your window AC. 

But how do you do this? Simple. Refill it with freon. In this post, we will teach you the hows and whys of recharging your window AC so read on. 

Why do you need to recharge a window AC?

Window AC units are generally sealed and ideally, they do not require constant recharging at all. Recharging your window AC is dependent on two reasons only: freon is too low, or it has developed a leak somewhere. Having said these, you need to recharge your window AC for the following reasons: 

  • For you to have a constant source of cool air to be distributed in the room. 
  • When it leaks, back vents will start blowing hot air.
  • The AC is consuming more energy, leaving a large dent on your electric bill.
  • The refrigerant line might develop ice buildup in the long run.
  • The refrigerant line will start emitting hissing sounds. 
  • The AC clutch will be broken. 

Sometimes, the leak causes more than just one problem and it is important for you to square all these causes for you to make the proper intervention for your window AC. With our dependence on AC systems nowadays, recharging them has become more of a maintenance step for it to be around longer.

Related: How To Clean A Window Air Conditioner Without Removing It

Materials and tools

Just a word of caution, before you tinker on your AC on your own, make sure that your state allows that. Some states do not allow house owners to tinker on their ACs. If your location allows you to, here are the materials and tools that you should gather: 

  • Leak detector
  • Refrigerant
  • Freon kit
  • Screwdriver
  • Gloves
  • Eyeglasses for protection

How to recharge a window AC

Now that we know the basics about why you need to recharge your window AC, it is time to know the steps on how to do it yourself. 

1. Unplug the window AC

1 unplug window ac unit

This is always the first step in maintaining your window AC. It is more of a safety step which you need to do before you can check the internal system of your window AC.

2. Wear protective gears

There is a reason why gloves and protective eyeglasses are needed for AC recharging. The substance that you will fill it with, the freon, contains toxic elements. As a matter of fact, it causes blisters and frostbites on the skin when it comes in contact with it so never skip this part. 

3. Open the window AC’s case

Older window AC models are easy to open because you just need to slide the case off. Newer models would require a screwdriver for the AC case to be opened. You might need to consult your AC’s user manual for you to be familiar about the steps on how to open it. 

4. Start checking for possible leaks

4 check the leak

There are four methods that you can employ to check for possible AC leaks.

  • Use leak detector: Plug in the AC, open it, and just cover the back for it not to be exposed to draft. Take the leak detector and let it probe around the back parts of the AC unit. If there is a leak, the detector will light up and will emit a sound to signal leak. 
  • Use soap: Mix soap and water. Spray it around the refrigerant transmission gear. This includes the pipes, the hoses, and the valves. After this, turn on the AC and if bubbles form in those areas, your window AC has a leak. 
  • Use dye: For this, you specifically need a fluorescent dye. Spray the refrigerant with this dye. The refrigerant will circulate the dye and will pool on leak sites. If you have a UV lamp, you can use it to detect where the leak is.
  • Use nitrogen: This is only reserved for professionals. The valves of the AC system are closed and then nitrogen is used to pressurize it. A monitoring gadget is attached to measure the pressure. If the AC’s pressure turns low, there is a leak. 

Related: Is A Freon Leak In Your Home Dangerous? – Causes, Symptoms, Treatments

5. Fix the leak source

If the leak from the window AC is slow, all you must do is to refill the AC with freon. But if the leak is too fast, you will have to solder out the source of leak and then add freon to boost the cooling system after. 

6. Connect the AC’s valves to its compressor

Locate the compressor using your user’s manual. There should be two connectors attached to it. Next, attach one of the two compressor’s lines to the service valve found in your freon kit. After that, attach the tap valve. 

7. Attach the valves to the freon dispenser

refill the ac

As have been mentioned, your freon kit comes with two valves. Check the freon kit for the diagram that will teach you how to connect the valves with the freon dispenser. Position the freon dispenser in between the two valves. 

8. Recharge the window AC

Make sure that all valves and lines are connected to where they should be connected. Check for wheezing sounds or air leaks. Read your user’s manual and identify the volume of freon required by your AC brand and model. After that, turn on the AC and set it to the highest power setting. 

As it runs, the refrigerant shall fill the AC with freon. Check the freon gauge and see if it has met the freon limit. When it has gotten its fill, turn down the AC into the lowest power setting. Let it run for at least 10mins on that setting. Next, unplug the AC, remove the valves attached to it. Check the performance of the AC if it has gotten cooler. 

Can an AC be undercharged? 

Chances are, your window AC needs recharging because it was undercharged when you bought it. This is not your fault to begin with, but you must face the consequences. If you are suspecting something, you can buy a freon gauge and check if it is undercharged by comparing it with the required freon capacity (which you can find in the user manual). So, to answer this question, yes, your AC can be undercharged. 

How long can freon last? 

In theory, freon lasts forever (and this is not an overstatement). The AC’s refrigerant transmission gear is a sealed system. As such, no freon should be able to escape your AC system. But when there is a leak in your AC, the freon will escape. This is the reason why you need to recharge your AC at some point. 

To expand the answer, freon does not go bad either and ideally, there is no rule of thumb as to when you should have it filled or changed. As a matter of fact, it would be abnormal to lose freon in your AC. 

Is it bad to run window AC with a very low freon? 

Yes. Without the refrigerant (or freon), your AC can be overworked because it cannot dispense cool air. If it is overworked the compressor can be damaged. If the damage is prolonged, you are looking for possible overheating and at least $150 (and more) of repair costs. 

Can an AC be low on freon without leaks? 

In some instances, yes. This is the reason why an annual AC tune-up should be done. Regular servicing and maintenance give you an edge in knowing where the freon loss is coming from when it is visible that there is no leak in your window AC’s system. 

When to call a professional?

Part of recharging the window AC is checking for leaks in the compressor and refrigerant gear. Sometimes, fixing it requires more than just soldering the leaks. If the damage is way beyond your capacity and knowledge, you must call for professional help. 

How much does it cost to recharge a window air conditioner?

Recharging a window AC is part of the maintenance procedures to ensure its longevity. As such, you must invest in this once in between 1-2 years. Hiring someone to recharge your window AC will cost you in between $100-150. DIY window AC recharging is just about $50 max. This includes gauge and freon kits. 


Homeowners with window ACs would not know when to recharge their AC units until they need to. This is often signaled by hot air coming out of the AC or if its cooling performance has significantly lessened. While leaks are probable causes, it might just be a matter of recharging it with freon, which, as we have emphasized here, is completely doable. 

However, you must check first if your state allows you to do these maintenance checks. If not, might as well consult with a trusted AC/freon technician.