I think I need a new heater core. My heater is blowing smoke that smells like antifreeze even when off. I have a 1991 Wrangler, and it has the after market Chrysler A/C. Do I have to remove the A/C unit to get to the heater core? If so, can I do that w/o losing the freon? If not, how do I get the assembly out? The Chilton manual is not very helpful.