2009 Toyota Corolla radiator

No vehicle has a shutoff valve to prevent the freon from escaping. Its supposed to be a sealed system already so manufacturers are never going to install unnecessary components just to help a mechanic whether its a professional mechanic or any do it yourself mechanic. Even if a small valve only cost $5 to create and install into a vehicle, multiply that by thousands and thousands, and the manufacturer is now spending too much in their eyes. So by not doing that, they save millions. Whenever the AC system needs to be opened, it needs to be evacuated and recovered in a proper manner. Freon is harmful to the environment and to the living. Make sure you're in a well ventilated area because freon has a boiling point of about -15 degrees fahrenheit so as soon as it hits our atmosphere, it boils and you can no longer see it.

I'm assuming your setup for the AC is connected to the radiator. If thats the case, like I mentioned before, it needs to be recovered with specialty tools. If you choose not to take my advice on this and just disconnect the ac line, it will shoot out until its empty so be careful. If you're replacing the radiator, fill the radiator with coolant and then the ac needs specialty tools again in order to vacuum out the the air and moisture that went into the lines and then refilled with the proper amount of freon.