AC help!!

[bees]

i have a 95 s14 and the ac starts out cool but then begins to warm up. after a couple minutes of warm air, i can hear the ac compressor (idle changes) go at it and then the air is cool again. it goes through this cycle in repetition and i wanna know if i can fix this problem? ive tried adding a bottle of R-134a freon through the low ac line (the one that sits lower in the engine bay next to the exhaust manifold) but nothing has changed. is this normal? how do i get the compressor to run continually and blow cool air? dont know how much is covered here on the s14's ac system, but i did search. please help! thanks!