AC works when it wants to

So I have been having a A/C problem and it is blowing my mind.
One day I can start it up and A/C blows cold and compressor runs and the next day compressor will not kick on. Later that day works fine. Two days later compressor will not kick on. Just trying to show how random it is. When it runs I have checked on gauges 40 low, 300 high, 99 degrees with eighty percent humidity.
Would love some input on this.