How to Recharge a Window AC Unit? (10 Easy DIY Steps)

How to Recharge a Window AC Unit

Is your window AC working hard all day long but not keeping you cool? Could it be that it needs to be recharged? Let’s take a closer look.

What to Check First 

1. Dirty Air Filter – Most small AC units have a removable air filter near the front. Remove it and clean it according to your User’s Manual. Try running the AC while you have the filter out for a few minutes to see if it starts blowing cooler air. That might have been your problem. 

2. Heavy dust or debris on the condenser or evaporator fins – Air must be able to pass freely through the unit to cool properly. 

3. Fan not spinning. It’s possible that the fan has come loose. A small set screw might need to be tightened on the collar of the fan. 

If your window AC fan is spinning, if it’s relatively clean and won’t blow cool air, it might need to be recharged. 

Hire a Professional? 

A professional HVAC technician can do this for around $100 to $150. You’ll have the peace of mind knowing that it was done properly and your AC unit will perform at its best. 

How to Do It Yourself 

Two important things to know about DIY recharging of a window AC unit are: 

1. The refrigerant (commonly called Freon) is in a sealed system and will normally only get low if there is a leak. Look for any sign of leaking refrigerant inside your unit. It will usually be greenish-looking corrosion. If you see this indication, the leak must be repaired before recharging. This is a completely different, much more complicated issue, and your best option might be to consider a new unit. 

It is possible, however, that a leak is so small that a recharge will last several more years. In this case, the second important thing to know is: 

2. You must use the same refrigerant as the unit already has in it. Very old units were made using R-22. Units built since about 2000 have R-410a refrigerant, and it remains the most popular refrigerant type. Many units built in the last few years contain R-32. Look at the label on your window AC to determine what type of refrigerant yours contains. R-22 is no longer produced and is available in very limited supplies. As a result, it is very expensive – and if your unit uses it, you are money ahead buying a new window air conditioner. 

Related Article:What if My AC or Heat Pumps Still Uses R22?

Many recharge kits that are sold online and in auto supply stores use R-134a. These are for automotive AC units and are not recommended for residential AC units – even though some people use them. 

What You Will Need to Recharge a Window AC Unit 

Freon refill kit

Freon refill kit

tap valve

A tap valve

  • Refrigerant – R-410a Freon refill.  A 2 lb. container costs about $70. (R-134a is way cheaper – but don’t do it!) 
  • Freon refill kit for R-410a. About $30. This should consist of a gauge with a hose connected to each side of it. Be sure to get the proper type of gauge for the type of refrigerant that you will be putting into your AC. 
  • A tap valve (bullet piercing valve) to install on your window AC if it doesn’t already have one. 
  • Screwdriver – either flat blade or Phillips head. 
  • Protective eyewear is recommended when handling refrigerant. 

How to Recharge a Window AC Unit 

1. Unplug the unit and remove it from the window. 

2. Slide the unit out from its cover. This may require a screwdriver. It usually slides out the front. Place the unit on a table, workbench or other suitable place where you can work on it. 

3. Check for a leak or leaks. Use a flashlight to look for any greenish corrosion on the copper tubes or on the condenser or evaporator fins. You might even find a pool of refrigerant somewhere. If a leak is found, it must be repaired before recharging. If no leak is found, proceed to step 4. 

4. Look for a service valve. It will look similar to a tire valve with a cap on it. This will be on the low pressure (suction) line to the compressor. There will be two copper lines connected to the compressor; the low pressure side is the larger of the two. 

Note: Many window AC units do not have a service valve and one must be installed in order to recharge the AC. See How to Install a Service Valve (below). Then proceed to step 5

5. Connect the refrigerant can to the end of the hose of the Freon refill kit with the turn screw on it. Turn the screw all the way in to pierce the can, but do not turn the screw out (open) at this time.

6. Remove the cap on the AC unit’s service valve and connect the other hose from the kit to it. 

7. Plug in and turn on your AC unit with the temperature turned down to call for cooling. If it has knob controls rather than digital controls, turn the knob to Lo Cool. When the compressor starts, the needle on the gauge should move to the far left side of the scale. 

8. Open the turn screw on the Freon refill kit to put Freon in the window AC unit. Follow the instructions included with the kit to be sure you are doing it correctly. You might need to open the turn screw for a few seconds, then close it to check the pressure. 

9. When the gauge reads approximately the correct pressure specified in the instructions, close the turn screw to stop the flow of refrigerant into the AC unit. 

10. Turn off the AC unit, remove the refill kit hose. Put the cover on and reinstall your AC in the window. 


Normally, the refrigerant in a window AC will last the lifetime of the unit – often over 10 or even 15 years. Proper maintenance, especially cleaning any dirt and accumulated dust off the inner parts of the AC will help keep the copper components from corroding and developing leaks. 

It is not especially easy to recharge a window AC unit, and many states restrict the handling of refrigerants to those who are licensed HVAC technicians. Be sure to check your local laws and think through all that is involved before attempting to recharge your window AC unit. 

How to Install a Service Valve on a Window AC Unit (If yours doesn’t have one)

The service valve is the way that you can put Freon in your window AC unit from a Freon refill canister. Often called a “tap valve” or a “bullet piercing valve”, service valves are available online and at hardware stores for about $5.00. Be sure to buy the correct size for the copper tube on your window AC unit. Here are the basic steps for installing this valve: 

1. The compressor is a round can-shaped object with two copper tubes connected to it. Locate the low pressure (suction) copper tube connected to the compressor – it is the larger of the two. 

2. Clean a 2” straight (not curved) section of this copper tube with a small wire brush or steel wool. Carefully remove all dirt and corrosion to make the tube shine like a clean penny. 

3. Align both halves of the piercing valve on the tube so the valve will be easily accessible. Start the screws by hand. 

4. Tighten the Allen screws evenly with an Allen wrench (usually provided) until there is no gap between the two halves of the valve body. The inner rubber gasket will seal against the copper tube as the screws are tightened. 

5. Turn the center piercing screw all the way in to pierce the copper tube. Now the service valve  is ready to have the Freon refill kit attached to it.

Repair or Replace

Window air conditioner can last for 8-12 years. If your ac unit is too old to repair, replacing with a high EER rating ac is a better choice. 

Troubleshooting Post-Recharge Issues in Window AC Units

Even after recharging your window AC unit, you might still face issues with its cooling efficiency. It’s crucial to understand that while recharging the refrigerant can solve problems related to low coolant levels, other factors can also affect the AC’s performance. Here are a few troubleshooting tips to consider if your window AC isn’t cooling properly post-recharge:

  1. Check for Proper Airflow: Ensure that there’s nothing blocking the unit’s air intake or exhaust. Obstructions can significantly reduce cooling efficiency. Regularly clean the air filter and check both the evaporator and condenser coils for dirt and debris. Proper airflow is essential for effective cooling.
  2. Inspect the Thermostat: Sometimes, the issue might be with the thermostat settings or functionality. Ensure that it’s set to a cooling mode and the temperature is lower than the room’s current temperature. If the thermostat is not functioning correctly, it might need replacement.
  3. Examine Electrical Connections: Loose or damaged electrical connections can hinder the performance of your AC unit. Check all connections and circuits related to the AC. However, be cautious and ensure the unit is unplugged before touching any electrical components.
  4. Evaporator and Condenser Coils: Dirty coils can impair the unit’s ability to cool the air effectively. Clean the coils carefully with a soft brush or a special coil cleaning solution. Be gentle to avoid damaging the fins.
  5. Room Insulation: Sometimes, the problem isn’t with the AC unit but with the room itself. Poor insulation can lead to cool air escaping. Check windows and doors for leaks and consider using weather stripping or caulking to improve insulation.

By addressing these areas, you can ensure that your window AC unit operates at its peak efficiency, providing you with a cool and comfortable environment.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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