● Minus(air volume) Press once, the air volume of both two fans will decrease by. This action will have no effect on the fan, which is already on the lowest speed, but the air volume of other fan will decrease by 1. This action will have no effect on both two fans if they are already on the lowest speed.●Add( volume) Press once, the air volume of both two fans will increase by 1. This action will have no effect on the fan, which is already on the highest speed, but the air volume of other fan will increase by. This action will have no effect on both two fans if they are already on the highest speed.● Sleep mode: Press once to open the sleep mode, the both 2 fans will automatically switch to low speed. When all sign lights on LED display is black, and only the sign of (Sleep mode) is displaying press any button on the controller to wake up the screen, then the fan will back to work under automatic mode.●By-pass mode: Press once to open the by-pass valve. The function is same as the by-pass module on LED screen. Press again, to close the by-pass valve. ● Inner loop mode: Press once to open the inner loop valve. The function is same as the inner loop module on LED screen. Press again to close the inner loop valve.