Yes, you can evacuate a car AC with a vacuum pump. Here are the steps:
• Connect the vacuum pump's hose to the low-side service port of your car AC unit.
• Make sure that all hoses and valves are securely connected and sealed.
• Turn on the power switch of your vacuum pump and set it to its highest level.
• Monitor the pressure gauge carefully until it reaches 0 psi (pounds per square inch).
• Disconnect all hoses and valves once done evacuating the system, then shut off your vacuum pump.