The condenser service valve has a socket that connects to the manometer, when you screw the manometer to that socket that is like the one of the car wheel spikes you should indicate the pressure in the manometer as soon as you connect it either high or low HIGH: refrigerant gas pressure outlet LOW: it is the suction part the high and low valve as they call it, in the condenser it must be open, but the circuit does not work would not be sucking or expanding the refrigerant gas, what you have to have high and low serrated are those of the manometer, since the manometer It has the part of the center where the vacuum pump and the bottles are connected to charge and air will enter and the refrigerant escapes I leave you a 3D video how the pressure gauge works good luck