This question is asked often here, have a look back through some of the forum sections for this.
As you will understand, you are able to measure a steady state current but with an alternating current you will have troubles without some additional tricks.
Some people suggest using a software approach, where you detect and measure only while the current is in the positive cycle. This can be tricky if you're not careful.
A preferred solution is to place a precision rectifier and buffer after the ACS758.
Using this method will more likely give you a more accurate representation of the actual current in the conductor.