How to Inject the Dye Into the Air Conditionerby Kathryn Shimer
If your car's air conditioning has stopped blowing cold air, it most likely has a leak. Since refrigerant cannot get out of the system on its own, it must be leaving through a hole somewhere. In order to repair the air conditioner, you will need to find the leak by injecting ultraviolet dye into your AC system.
Follow the air conditioning hoses to the low side air conditioning fitting. Unscrew the cap. It will most likely be labeled with an "L", but if not, it is the fitting further from the condenser (which looks something like a car's radiator).
Attach the tube that is connected to the dye canister to the Schrader valve that was exposed when you unscrewed the "L" cap. You will attach the hose by placing it on the Schrader valve and screwing it on or by pushing down and holding it on.
Unscrew the bottom of the dye canister to allow dye to flow into the system. You don't need much, just a few seconds worth. Read the instructions on the dye leak detector kit to determine exactly how much dye you should put in.
Take the hose off of the low side fitting and replace its cap.
Run the air conditioner on full blast so that they dye will escape from the leak.