heater core went bad a few months ago and i figure i had better fix it before winter and i am frezzing.... i know that it is a whole weekend project where every dash piece has to come off inorder to get to the heater core, but i was wondering if it is posible to replace the heater core with out discharging all the R-12. the reason i dont want to discharge all of the regregerent is because i dont wanna convert to 134a and my car has really cold ac although i rarely use it.... thanks