When your window AC unit stops blowing cold air but is functioning properly in every other regard, it is likely low on coolant. This means that the unit will have to be recharged with a fresh infusion of coolant, likely Freon.
That isn’t necessarily a given though. Be sure to research what specific coolant your window air conditioner uses. If it does turn out to be Freon, you can buy a Freon kit, which will include all the tools and instructions necessary to get you through the AC recharge process.
Note that Freon is toxic to humans and any handling and safety instructions that come with your kit should be taken very seriously.
DISCLAIMER: Depending on your local laws, the use of refrigerants like Freon and even tinkering with the inner workings of an air conditioner unit are illegal unless you are specifically licensed to do so. Look into your local regulations and make sure that you are not breaking any laws by attempting a project like this.
Step 1 – Uplug The Unit
Unlike central air conditioner units, window air conditioners only draw power from the wall socket they are plugged into. Simply removing the plug will ensure that you can open up the machinery and inspect things safely.
Step 2 – Open the Air Conditioner
Some AC units can be opened by simply sliding the front ends out of place, while others will require the aid of a screwdriver. Consult the owner’s manual for your specific device to determine the proper method.
Step 3 – Check For Leaks
Having successfully opened up your window conditioner, you will need to carefully check for any signs of leakage. If you locate any leaks, fix them or call in a professional to do so before using the device again. If no leakage is present, consult the device's owner's manual to determine the proper amount of refrigerant you’ll need to add.
Step 4 – Attach the Valves to the Compressor
Using both the unit’s manual and the tools included in your Freon kit, locate the compressor part of the window AC and the two lines coming off it.
Next, take the service valve from your kit and attach it to the compressor line. The compressor should still have one free, unattached line extending from it. Take this remaining compressor line and attach it to the tap valve, which will also be included in the Freon kit.
Step 5 – Attach the Valves to the Freon Source
Attach both of the valves that you’ve just installed, the service and tap valves respectively, to your container of Freon. The kit should contain a detailed diagram showing how to properly position the coolant tank between the two valves.
Step 6 – Charge the Unit
When you’re assured that everything is connected tightly and properly with no potential for leaks, plug in your window AC unit and power it on at its highest setting. With the Freon tank now directly linked to the unit’s inner working via the service valve and tap, the normal flow of air that occurs while the unit is operational will push or “charge” Freon into the unit.
When the unit is finished taking in the amount of Freon mentioned in your user manual, power down the unit, unplug it, remove the valves from the compressor, and place the unit back in its housing.
Don't Hesitate to Call a Professional
To reiterate, in many parts of the country this work is legally restricted to people who are licensed experts. Assuming you can even legally attempt it, if at any point in the process you become confused or unexpected problems arise, stop what you’re doing immediately and call a professional. When this process is handled incorrectly is can be damaging to the window air conditioning unit and dangerous to the user.