A/C compressor spitting

I have a 99 4.o with approx 145K on it. Last summer my A/c quit working so I put some R134a into it twice during the summer.

Well it is starting to be A/C weather again and when I put my A/c on it was warm again. So I went and got a can and the pressure was reading 25 on my gauge so I started adding. When I finished the back end of my compressor started spiting it all out into the engine bay. there seems to be a port of some sort right in the middle of the back of the compressor. The pressure goes back down and when I add more it just spits it out of the compressor. What is this port and what does it spitting mean? I am guessing that it means my compressor is bad but am unsure.

I tried searching but could not find anything else about it?

O ring in the high side schrader(sp) valve worn?

It a high pressure relief. You likely overcharged it. You also have a good size leak if you needed to top it off twice in one season.

You should take it someplace to have it evacuated, leak tested and recharged properly after fixing any leaks.