a/c tries to kill motor since battery change.

The exact same thing happened to me. I removed the throttle body assy and cleaned it with carb cleaner. Restarted engine with A/C off. Drove for 20 miles. Now it's running fine. See this link: http://answers.edmunds.com/question-after-changing-battery-2002-chevy-trailblazer-turn-heater-car-rough-idle-2825.aspx

I HAD SIMILAR PROBLEM.ALL I DID WAS ADD A CAN OF REFRIDGERANT WITH OIL OR THE ONE THAT HAS THE OIL ALONE, CAUSE YOUR A/C "WHERE U CONNECT THE HOSE" DOESNT HAVE SUFFICIENT OIL 2 MAKE THE COMPRESSOR NOT LOCK-UP OR GET YOUR A/C SYSTEM FLUSHED OUT.ANOTHER THING COULD BE TO CLEAN YOUR THROTTLE BODY OUT WITH THROTTLE BODY CLEANER OR CARB CLEANER....