my 2000 s10 ac compressor stays on all the time the clutch does not stop running

Yes it should turn off and on,check ac relay,or maybe pressure switch.

I have a Chevy s10 2000 I change the a.c. compressor and lines a year ago ...The a.c. stop blowing cool air but just brought 2 Freon three weeks ago put it in and it only lasted a week then my a.c. went back hot again... what should I do now

You have a leak in your system, you can put some leak detector (r-134a uv leak detector dye) into your system, then go over the tubing with the light you should see the dye spraying out where the leak is.

With a uv flashlight that is.