go to a trusted mechanic first to let him rule out compressor problem. kung compressor daw talaga ang may problema, tsaka ka pumunta sa aircon specialist.
check mo muna yun idle up/vacuum switch mo. it should work when you turn on your a/c. this would compensate for the added load of your compressor. if you can't find it take it to a reputable aircon shop ike mang marios or the bankers in marikina.