The pressure switch is not adjustable. The spec of the switches are as follows. This is from the Official MBZ w126 manual. It should be similar for w123.

Low pressure - OFF at 2.0 bar, ON at 2.6 bar
High side - OFF at 15.0 bar, ON at 20.0 bar.

The manual uses BAR. You can do your conversion to psi, pascal. There are a lot of experts around here on AC.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.