Just replaced my heater core and now my AC needs recharged. Do i need to have a vacuum pulled on the system?

 

Yes you do.

 

That's what i thought, Thanks.

 

If you recovered the refrigerant from the system completely discharging it, yes you must pull a vacuum on the AC system before trying to recharge it. If it still has a charge in the AC system you can probably just add refrigerant.