Might need two switched plumbed in a T, one for lower pressure, one for the higher pressure. Then a relay controlled by the switches. Use the ground from the high pressure switch to the relay coil ground, This will close the relay at the higher pressure setting. Wire the lower pressure ground to a one side of a set of NO contacts on the relay, jumper the other side on that pair of contacts to the relay coil ground, this will let the low pressure switch control the opening of the relay. Remember to wire the relay coil + to a switched 12V source.

On the second set of NO contacts on the relay run a ground to one side then run the other side to activate the circuit.

How this circuit will work is like this. As the pressure rises the low side switch will make, since it is going to a set of NO contacts on the relay the signal stops there as the relay is deenergized. Pressure continues to rise until the high side switch makes, this sends a ground to the coil negative, if you remembered to wire the coil + then the relay closes. With the relay closed you now have both sets of NO contacts closed. Your circuit will energize. The ground from the low side is now applied to the relay coil - as well. At this point both the high pressure and low pressure switches are applying a ground to the relay coil -, not a problem. As pressure drops the high pressure switch will open and remove it's ground from the relay coil -, but the low side ground will still be there thru the now closed contacts. Once pressure drops enough for the low pressure switch to open the ground will be removed from the relay coil - and the relay will open removing the ground from your circuit. At this point pressure will have to rise enough to close the high pressure switch and the cycle starts over.

Short of finding an adj hi/lo switch this is how I would do it.