Helping my dad pull the 318 out of his 72 challenger, but not sure what to do about the AC system

As the title says, we’re not sure if it’s pressurized as the ac hasn’t been used in probably close to 30 years, and the cars only ran a couple times in that time. We’re pulling the engine and need to disconnect the ac, but don’t want to crack it and hurt ourselves. Is there a way to safely crack the AC? Do we have to vacuum the system?