1) Turn off the compressor and remove the cover from the switch exposing the adjustment nuts. Be sure not to touch the electrical terminals, turning the circuit breaker off is recommended.
2) You will see two nuts with springs under them. The larger one is to increase the pressure clockwise and decrease the pressure going counter clockwise. The smaller is for your differential. We factory set these at 145PSI.
3) To adjust the pressure ranges turn the nut on the large central post clockwise to increase the pressure range. Turn the nut through 3 1/2 rotations to increase the range by 10 psi. For example, if the current range is 20/40 psi, which means the pump cuts in at 20 psi and cuts out at 40 psi, turning the nut through 3 1/2 rotations increases the range to 30/50 psi. Turn the nut counterclockwise by the same amount to decrease the range.
4) To adjust the differential Turn the nut on the smaller of the two posts clockwise to increase the range between the cut-in and cut-out pressures.