2003 f150 lariat air conditioning recharge

where is the low side and high side on the air conditioning lines. i have heard that the low side has a blue cap. i do not see a blue cap at all. with the hood up and looking down at the engine, i see a black cap to the left of the radiator about half way between the front and back of engine compartment. on the right side of the engine i see a green cap mounted right above the firewall. need to recharge my air