After the air compressor has been empty for a long time, the signal light will be on. At this time, the joint control host will automatically switch to the running timing function to continue timing, but the joint control cabinet cannot start the machine. That is, when the working pressure is low enough to reach the joint control cabinet’s starting pressure, the machine can only be controlled to start by the pressure switch of the machine. Similarly, when the joint control host automatically switches to the running timer and rotates to the machine, it will become the main machine, and the machine cannot be started. After the signal is eliminated, the joint control returns to normal.