How To Recharge A Window AC Unit? (10-Step Freon Refill)

Here’s the thing: Window air conditioners can spend their whole lifespan without recharging. Refrigerator lines are a closed system (unlike car ACs, for example); the R22 or R401A refrigerant can’t escape and doesn’t need to be replenished.

So why do we wonder how to recharge a window air conditioner?

It’s all had to do with time. When window AC units become older, the closed Freon system can not be as wholly closed as we hope it would be.

If you’re trying to figure out how to rechange a window AC unit, you probably have an even bigger problem to worry about: A leak in the refrigerator lines.

Leaking window AC results in depletion of Freon and the need to replace the Freon manually. However, before recharging the AC, we need to deal with the primary issue at hand: The leaking window AC.

diagnozing if window ac stopped cooling due to low levels of freon
Window AC not cooling like it used to? Low levels of Freon might be the reason why, but the primary root of the problem is usually a leaking refrigerant line.

It makes little sense to put Freon in a window air conditioner if we know there is a leak. It’s like trying to add air to a car tire with a hole. No matter how much air (or Freon in our case) we put in, the air will still leak out.

Another thing we have to considers is this:

How do you really know if your AC is low on Freon?

In other words, your window AC doesn’t work, how do you figure out if the problem is the lack of Freon or something, well, anything else?

To put it simply: Yes, you can rechange your window air conditioner yourself. It’s not the easiest job in the world, it does require specialized HVAC equipment, but with the right attitude, it can be done.

To learn how to properly recharge a window air conditioner, we will use the classic 9 step-by-step Freon refill guide. Here is how it has to be structured for everybody to actually rechange the AC adequately:

  1. How to check if your window AC is actually low on Freon (Steps 1-3).
  2. How to locate the leakage and fix it (Steps 4-6).
  3. How to properly refill the Freon into the refrigerant lines (Steps 7-10).

Important note before you start: Safety first! Adding Freon to a window AC unit can be dangerous; you can hurt the unit or yourself. Make sure to follow the required safety measures like turning off the thermostat wiring, breaker, and weaving safety glasses, gloves, as well as using proper HVAC equipment.

In the US, every homeowner is permitted to add Freon to the AC. However, if you find the job too difficult, the EPA requires you to hire a professional with proper certification for rechanging your AC unit. Below the Freon replacement guide, you will find a way how to contact professional HVAC technicians to help you out.

Diagnosing If Low Refrigerant Levels Are The Actual Problem (Steps 1-3)

A window AC that is low on Freon will still cool but as it used to. It’s the same principle with a hole in a tire; you can still drive but not as far.

Determining a mid-level decrease in the output airflow temperature is the main indicator of low levels of refrigerant. To test if the decrease in the output airflow temperature is actually mid-level (not room temperature or properly cool), we’ll use one of the simplest HVAC tools – a digital thermometer.

Step 1: Measure The Temperature Of Window AC Airflow

This is quite straightforward. Get close to the air handler with a ready digital thermometer. It will take about a minute at most to correctly measure the temperature.

Probably you’re trying to figure out if Freon needs to be changed because the airflow from your window AC is not as cold as it should be. We are just measuring this to make sure the difference in temperature is in line with low Freon levels problems.

Step 2: Measure The Room Temperature

Room temperature is the benchmark. We’ll need it to calculate the difference in temperature that the window AC unit is still capable of making.

Use the digital thermometer to measure the room temperature and note it down.

Step 3: Calculate The Temperature Difference Window AC Is Still Capable Of

Calculate the difference between the measured room temperature and the temperature of the window AC output airflow.

Example: Room temperature = 86 °F. Airflow temperature = 70 °F. The difference is hence 86 °F – 70 °F = 16 °F.

checking if you need to refill freon to a window ac
By accurately measuring the airflow temperature difference we can get a good idea if low Freon levels are the actual problem.

Here is a rule of thumb to get an idea if leaking Freon is truly the culprit:

  • If the temp. difference is higher than 20 °F, you don’t have to change the refrigerant. Cleaning the filters will probably do the trick.
  • If the temp. difference is between 10 °F and 20 °F, you most likely have a Freon leak. This calls for window AC refrigerator recharging.
  • If the temp. difference is below 10 °F, you have a more serious problem than leaking Freon. You can check how an HVAC technician fixes AC’s that aren’t working properly here.

Locating The Freon Leak And Use A Quick Fix To Seal It (Steps 4-6)

Fixing a refrigerant leak seems, at first, like a daunting procedure. And it’s true; for bigger systems like central AC units and ductless mini-split systems, you should contact your HVAC guy to seal the leak.

Fortunately, however, you can deal with small leaks yourself. First of all, however, you have to expose the refrigerant lines and find exactly where the Freon is leaking:

Step 4: Unmounting The Window AC And Exposing The Refrigerant Wires

Your window AC unit, be it a saddle unit or one of the quieter window AC units, is installed on the window. Unplug the unit, clear away the installation kit, and take it down to be able to fix it. Most DIY enthusiasts do this in their garage.

Use a screwdriver to undo the panel on the unit (usually located on the backside of window AC units; the side facing outdoors).

First, locate the compressor. It looks like a car battery, usually colored black.

Secondly, note the two lines that go from the window AC unit’s mainframe to the compressor. These are the refrigerant lines; one delivers Freon to the compressor and the other is the Freon outflow line.

Be aware that both of these lines contain R22 or R410A refrigerant that is under high pressure.

Step 5: Locate The R22 Or R410A Leak

Go along both refrigerant lines and look for leaking Freon. Chances are there will be a small pool of R22 or R410A, depending on your refrigerant, under the leak. That’s the easy detection.

In most cases, detecting the leak is not so easy. HVAC technicians use several methods like dye detection, electronic detection, nitrogen detection, oil detection, and even soap bubble detection to locate the leak in bigger units.

In a smaller unit like a 10,000 BTU window AC unit, it’s much easier to detect the leak by careful visual observation of the Freon lines.

Finding and sealing the leak is essential for the refrigerant recharge to be effective. Here’s how you seal the leak:

Step 6: How To Seal A Refrigerant Leak

With bigger units, you will need specialized HVAC equipment to seal the leak. If, however, you are dealing with a small (15,000 BTU or smaller) window AC unit, you can do that yourself with something as simple as a Freon leak repair kit.

Basically, these kits are easy-to-use, no pump downs or syringes needed “glues” that seal the leak of small AC window units. They are made specifically for non-professionals who are trying to recharge an air conditioner. The best-selling direct injection Freon kit is the Leak Saver; it costs about 40 bucks, you can get it here.

Here is a photo from their marketing material (might sound a bit over the top) but the important thing is that this Leak Saver actually does the job of sealing the window AC leak very well:

kit to seal refrigerant lines leaks before you put freon in

Once you have sealed the leak, you again have a closed system. Now you can confidently recharge the refrigerant lines of the window air conditioner with the – important – the right refrigerant.

Recharging Window AC Unit With Freon (Steps 7-9)

Now, we can finally learn exactly how to put Freon in a window air conditioner.

Here is the essential part:

Use the right kind of Freon. You can’t put R22 refrigerant in a window AC unit that uses R410A, for example. Check the specification sheet or the label on the unit; you will find exactly what type of refrigerant you need to recharge your window air conditioner with.

Recharging the AC will require some specialized HVAC equipment like gauges for Freon charging. If you don’t have one, you can check Step 8; there you’ll find a $30 gauge set for Freon charging that you can also use with car AC:

Step 7: Locate Freon-Adding Line And Attach The Tap Valve

You have two refrigerant lines, but there is only one in which you can add Freon. First of all, we have to locate that one. It’s usually the larger of the two lines; some refrigerant lines also come with an ‘Add Freon Here’ description on the line.

Once you have the right refrigerant line to add refrigerant into, attach a tap valve. You will find all the directions on how to attach a tap valve to the refrigerant line on the documents that came with the valve. Follow them and have the tap valve attached. That’s the 1st step in recharging a window AC unit.

Step 8: Connect Gauges And Release The Air From Refrigerant Lines

If the Freon was leaking, there is a change that it was replaced by air. Before we can put the Freon in the window air conditioner, we have to release the accumulated air located within the refrigerant lines.

First of all, check the gauges and make sure they are turned off. Now we will use the tap valve we have just added.

Connect the blue tube to the:

  • Tap valve you’ve just installed.
  • Compound gauge.

If you don’t have a set of gauges, you can easily get them.

gauge set with described parts for recharging a window ac unit with blue, red and yellow lines
Cheap gauge set for freon charging for R134A, R12, R22, and R502 refrigerants. You can notice the blue and yellow lines; these can be used to recharge window AC units. You can get it here for about 30 bucks.

Do note that this cheap gauge set will work for R22 refrigerant but not for R410A refrigerant. R410A refrigerant gauges are more expensive: the best one is by Yellow Jacket and it costs about $150. You can get an R410A gauge set for AC units here.

After you have attached the blue tube properly, put the window air conditioner in the maximum output fan speed setting (usually designated as “High” or “Turbo”). Keep it running at that maximum airflow output for 5 minutes so that the remaining Freon starts flowing.

This is very important: Take the correct Freon bottle. R22 for R22 window AC units, R410A for R410A units, and so on.

Connect the Freon bottle containing refrigerant you will recharge your window AC unit with to the yellow tube. When the connection is secure, open the freon valve.

To release air, loosen the at-gauge yellow tubing for a bit. Keep it loosened for 2 seconds before tightening it back up. This simple process will remove the excess air from the refrigerant lines.

Step 10: Putting Freon In The Refrigerant Lines

To start adding the Freon into the refrigerant lines, open the low side valve only (opening the high-pressure valve can be extremely dangerous; leave it closed). Now you’re actively pouring Freon into the refrigerant lines.

It’s kind of like adding pressure to a car type, right?

The one thing you need to know is when the window AC refrigerant lines are recharged (completely full). There might be some variation between different types of refrigerant lines, producers, and Freon type but most commonly you are recommended to stop the Freon input when the pressure on the gauge reaches 70 psi.

When you reach 70 psi, the window AC units have been fully recharged. Job well done!

Remove everything: The gauges, Freon, and remove all the tubing.

The last step is to make you close the new valve you’ve installed. When you remove the blue tube, just keep in mind to close that valve, and you have successfully put the Freon in the window AC unit.

I Can’t DIY This: Who Do I Call?

This is the basic 10 step way how to put Freon in the window AC unit. Hopefully, everybody with a bit of technical skills can use it to recharge a window air conditioner on their own.

However, the task of diagnosing, finding, and fixing the leak, and putting Freon in the big refrigerant line is quite daunting and it’s completely understandable that most people would prefer help from a professional.

Do keep in mind that while you can add Freon to a window AC yourself, EPA requires that everybody you hire to do it for you, has to have proper HVAC certification to recharge the unit.

All in all, you can DIY add Freon to a window AC unit using this 10 step-by-step guide. Hope this helps.

14 thoughts on “How To Recharge A Window AC Unit? (10-Step Freon Refill)”

  1. There are two methods for recharging a window air conditioner, the low-cost backyard quick method used by many homeowners, or the HVAC tech method which is more involved but recommended.

  2. Make sure you have worn the gloves as well as the protective eyeglasses before you proceed. Freon, the refrigerant that you’ll be refilling, is toxic. It is also cryogenic and can cause frostbite if you allow it to come into contact with raw skin. So please take all the necessary precautions that you can.

  3. Hi there – I’m not quite sure I understand the temperature measurement test.

    If my air conditioner is working correctly, I *expect* the air flow from the air conditioner to roughly match the room temperature, because that’s why I turn the air conditioner on – to cool my room. So the temperature test of “less than 10 degrees Fahrenheit” indicating a major air condition problem doesn’t make sense to me – why should I expect it to be any other way?

    Similarly, if the air conditioner isn’t working – why would I expect the air flow to be a different temperature from the room temperature either? An air conditioner blowing hot air will be the same hot air in my room as well.

    I don’t understand.


    • Hello James, a very good point. The ‘room temperature’ refers to the temperature without any air conditioning. 72°F is commonly referred to as room temperature but in summer months, this number can go past 80°F. You’re right, it’s not absolutely clear from the text.

  4. What about Superheat and or sub cooling, with high humidity or a high wet bulb you will never get 20F drop across a coil, this explanation shouldn’t even be posted. On top of that homeowner or not YOU ARE REQUIRED to have an EPA license to purchase refrigerant, and since R-22 was phased out years ago, now most units are R-410A and new units are R-32, you will pay more for R-22 than a new unit, not even accoiunting for much higher efficiency.

    • Hello Jeff, thank you for noting your concerns. We do warn everybody that recharging a window AC unit is not only difficult but can be dangerous. The specific situations – as you’ve explained very well – make the task even more difficult. EPA does require ‘proper certification for rechanging your AC unit’.

    • Jeff L, In my area, Eastern Missouri I cannot find an A/C company that will work on a closed system at all. They all want the easy replacement job instead of repairing an existing unit.I would gladly pay a tech or company to fix my unit but no one wants to do the work.

    • No one needs any kind of license to purchase any kind of Freon. The idiotic “license” is needed to use the mess. And not having a “license” has never stopped anyone from doing anything. Wake up. Anyone can purchase 5lb and 25lb tanks from Ebay and elsewhere, no “license” needed.

  5. For those who can’t do the work (or isn’t worth the cost of refrigerant), contact the wall unit manufacturer to see if it’s under warranty or Google the nearest authorized service center. It may be out of warranty but you should be able to pay a service fee to have it repaired. With inflation, the cost of a repair may make more sense than buying a new one, especially when you take into consideration the cost of re-configuring the in-wall hole to accommodate a new unit.

  6. Can’t you use the cheaper gauge set to remove the air from the lines. Then, using just a connection from the Freon to the AC without a gauge open the fill connection, let in some Freon, and measure the output air temp. Continue until it reaches an acceptable temp. That does away with the need to purchase the more expensive set of gauges.

    • Hi Steve, that is doable but it is less straightforward. It is hard to DIY recharging a window AC unit; we hope your input helps somebody use a cheaper set of gauges to charge the freon.

  7. I guess you cannot fix a window AC with simple DIY since most new window-type ACs do not have the service ports comparing to the split ACs which normally have suction/discharge service ports.

    Unless it was previously repaired and re-charged with refrigerant and somebody brazed a new service port.

    • Hi Ray, yes, it is a dangerous job. That’s why the new window AC units don’t come with the convenient service ports. A HVAC guy will know how to do the job.


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