ac solenoid?

[PowerdbyChevy79]

whats up brothers.. have an issue and ive never encountered this before.. I have a68 with a 400 small block with a thumpr can, 650 edelbrock, vintage air setup nothing fancy.. my issue is I have it idled at 900 rpm when I put it in gear it goes down to about 700-750 rpm.. but when I turn my ac on.. it drops to about 500 rpm.. sometimes even dipping to the 400.. ive messed with the timing but nothing helps.. my buddy told me that I need a ac solenoid.. never heard of it.. does anybody here have any experience with this issue