1993 acura legend ac problem

getting good power to everything such as relays , fuses, and the high pressure switch , the compressor is good as it holds good pressure. altho ive vaccumed outthe freon and recharged one can into the system . the system baely took the one can as i think there is a machine to do this correctly? my issue is .. i know i need atleast 30 pounds of pressure in order for the clutch to engage correct? i need to know if this is true or not. basically. i had the car for four months. the ac blew slightly cool and then when stepped on the gas peddle a little, the ac blew colder. then at idle it went back to a little cool. so i fugred it needed more freon. like isaid i did the vaccum o nthe compressor nd checked the pressure gauages and shot in one can barely into the system as it hesistaed to take the can .it held the can good with no leaks suspected. turned the ac on and the clutch did not engage. now please help. im stuck. is it because im low on freon and i need at least 30 pounds of pressure for it to engage? or is it something else like my PCM module not serving power to the compressor to turn on at all?. please hlp as arizona is hot right now ! thanks.