Close the high side manifold. Remove the high-pressure hose from the high side of the AC unit. The high side hose is the red hose. Only remove the hose if your hose has a low loss fitting. Low loss fittings are used to conserve refrigerant. If you don't have a low loss hose, you could get frostbite from the refrigerant. Turn the hose counterclockwise to remove the hose from the unit.
Bleed the high side hose by screwing the hose onto the high side of the manifold. Open the manifold on the high side to transfer the pressure to the low side of the manifold.
Close the high side manifold. Close the low side of the manifold. This is the blue gauge. Turn the blue hose counterclockwise at the service port to remove it from the AC unit.
Screw the low side hose to the low side manifold. Replace the service port caps after you have removed the hoses.