My Air Conditioning doesn't work, but it makes a loud hissing sound?

First off, this is an air conditioning problem with my Honda Accord 2001 EX, 4 cylinder 2.3 liters.

Okay, here's the problem. Since last summer, i've had to put freon in my car, so i get AC pro, connect it and put freon, then everything is fine. This summer, i did the same thing, the air worked for a bit, so i turned it off. I later used it that day again, turned the car off without turning off the air. The next day, i mistakenly left the AC and the heat on at the same time, because it was cold. Now It doesn't even blow cool air anymore. I tried everything. I even tried putting more freon, but the needle on the AC Pro is now in the "red" zone, which means not to put anymore. Trying to fix the problem, i went on the highway with the AC switch on and kept driving. It sounds like the compressor comes on, then goes back off by itself, it comes on again and goes back off by itself. Later while i was still driving, i started hearing a loud hissing sound which turns back off when i turn off the AC. Any help?

A snake is hiding in it