2001 Honda Civic Air conditioning

Hi, I recently bought a 2001 honda civic, but when I saw the car, the air was not cold even though I switched on the ac. I checked with a local dealer near my home, he told that it could be the freon is less and he charged it. But even after that it was not cold. Then he checked a switch and when he tried grounding the switch to battery the compressor started working and very cold air started blowing. As a temporary fix, he told that we can put a ground wire. But the problem with doing that is that the compressor is on all the time, whether I switch on/off the AC switch on the dash/control panel or not, the compressor is on and cold air blows. I am not sure if any of the pressure switch is having problem or any wire connectivity issue. Any help/direction you can provide will be of great help. I also want to know if this will be a easy/cheap thing to fix or an expensive one.