AC expertise needed please.

[jfnar]

The AC on my ’05 silverado isn’t working. The compressor cycles on and off about every 10 – 12 seconds. I hooked up a DIY freon kit and the pressure goes back and forth from about 15 to 70 but it doesn’t seem to be taking any freon. I jumped the low pressure switch and the compressor stays on. I replaced the low pressure switch but no change. Do I need to jump the low pressure switch to keep the compressor running while I try to add freon? Any suggestions will be appreciated.