The ac on my sons volvo was not coming on, so I assumed it might be low on refrigerant. However, when I jumper the wires to engage the compressor it would not come on. I never had this problem before. A couple of weeks later I tried the same thing and the compressor kicked, in a added some refrig. and the system worked fine. Came on by itself and ran like it should. The next time he went to use it, it would not work. Again I tried the jump the wires and the compressor would not come on. I know the compressor works and that the system is charged, so what could cause this strange behavior. Also, does anyone know why the fan blower will not turn off unless you take the number 5 fuse out. This is a climate controlled car.