Compressor Level?

Hi, it's hot here (around 92), my heatpump is blowing cold air but it's running all the time and he have hard time keeping up with the 75 degrees I ask for. On the heatpump of my neighbour the isolated line is very cold and sweating, mine is not sweating at all and it's much less cold. What could be the problem ? I'm a looking at something expensive ? Is there anything I can check myself before calling a technician ? thanks !

My ac stopped working yesterday. It's a Trane heat pump. It still blows air but it's not cold. It started making a whistling noise from the inside unit. The sound is coming from the copper pipes area in the attached pic. It's hard to pinpoint but I think it's coming from the round silver piece (regulator?) towards the back in the center of the pic. We've already checked the condensation drain pan (clear), the pvc drain (clear), and the pump (working properly). We even poured some water in to the drain pan and it drained and pumped out fine. Could it be just low on freon? Or that round silver piece gone bad? Thanks so much in advance for any suggestions. [URL=http://s207.photobucket.com/user/discretekarma/media/Mobile%20Uploads/image_1.jpg.html][IMG]http://i207.photobucket.com/albums/bb23/discretekarma/Mobile%20Uploads/image_1.jpg[/IMG][/URL]