start engine and then using the throttle cable adjustment get it to an idle of 1800-2000 rpm. Now set the a/c controls to full cold and the fan to next to highest speed. Now begin to add the refrigerant to the low side fitting (low side is the fatter of the two hoses going to compressor) very slowly. You can hold the can upright and then invert for a second about every 15 seconds until the sight glass on top of receiver-drier next to right side of radiator no longer has any air bubbles in it. There should be a label under hood with a/c system capacity on it if it is not gone.