Refilling freon in Chevy S10

For quite some time my truck has been blowing cold air and occasionally it would get a little warm then revert back to cold. Very inconsistantly consistant!!

So I figured that I was low on freon. So I drained the existing freon to emptuy in so I can put fresh freon back in the truck. When I drained it, I had no moisture of any kind come out. It was only air. Not sure if that was normal or not.

So I started the truck, put the air on low, and put the gauge/freon on the low side of the line. started filling. The compressor would kick on, the PSI level would drop, and after 2-3 seconds, the compressor would kick off. It did this over and over. When the compressor kicked off, the PSI level would sky rocket into the RED. When the compressor was on, the PSI would be in the green.

So I dont have much time to get an accurate reading of the PSI. I haven't even used half the can of freon. So it feels like I'm not getting anywhere. So I took the level that it was showing and put the cap back on. I turned the air on faster and it is blowing nothing but HOT AIR. there is not one bit of cold anywhere in these vents. no matter if i turn the air on 1/2/3 or 4. Its HOT!!

Am I not doing something right when filling it with freon?

With summer upon us, I NEED this cold air to be working. Can anyone help?