The way to adjust is as follows. Open the casing for the pressure switch (See Fig.1-3 or Fig.2-3); adjust the setting screw for maximum pressure (Turning clockwise makes activation pressure higher, so the pressure at which the air compressor stops running will be higher) and the setting screw for pressure difference. (Turning clockwise makes larger pressure difference, that is, the difference between the pressure at which the air compressor starts and the pressure at which the air compressor stops large is larger) respectively. Careful adjustment will make the activation pressures within the range set by the manufacturer.