You can tell if your system is working by looking at the u-tube.  Each system is installed with a u-tube monitor installed on the system piping.  One side of the u-tube has a vinyl tube plugged into the radon pipe.  The suction created by the radon fan draws the oil up the side of the tube connected to the radon pipe.  The difference in height between the two oil levels indicates the actual suction in the pipe induced by the fan in units of inches of water column.  If the two oil columns are level, the fan is off or not working and needs to be turned on or serviced.