Low freon would be my guess also. They sell a kit with a hose and can of freon for $20.00 at auto parts stores. The only bad thing is you do not know how high the pressure in the system is. If you raise the pressure too much it could cause more issues. I would try one can and see if that works,if not have it checked by a tech. I had same issue last year and I did this and it works great,good luck.