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The pressure switch functions by balancing the pressure applied from the inlet side vs. the spring tension from the adjustment screw(remove the black rubber plug from one end and you'll see a slotted adjustment device). As the adjustment reduces spring tensiion against the internal diaphragm, it takes less air pressure to overcome the spring tension and make/break the switch. As the adjustment increases the tension against the diaphram, it takes a greater air pressure to overcome the spring tension and make/break the switch. All devices of this type have an inherent dead zone. If the switch makes/breaks as the air pressure reaches 90 psi, lowering the pressure to 89.9 psi will not result in a reversal of state. The pressure will have to drop through the dead zone before the spring tensioin can overcome the air pressure against the diaphragm and make/break the switch. Put an ohmmeter across the switch terminals and run the compressor until the switch changes state. Record the pressure from the guage attached to the compressor side of the system. Slowly let the air escape until the switch reverts to its original state. record the psi. The difference is the dead zone. If you want a different range of pressures, turn the adjustment 1 turn ccw or cw and re-perform the experiment. continue until you get the results you need. This year they gave you two of thses devices. use one to turn it on and the other to turn it off if you like.
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