Jumping Low Pressure Switch For ACC

Hi again,

does anyone know which pair (of the four)of wires I need to jump to check the refrigerant pressure in my AC system? The clutch does not engage.

I can engage the clutch by doing the following at ac relay pins:-

Clutch engages by jumping pins 86 & 87b
and also pins 30 & 87b.
Should pin 85 be earth for the relay solenoid part? Only I cannot get my circuit tester to bleeb in trying this out i.e continuity from 85 to chasis.

Cheers