Grand Voyager 2004 2.8 CRD. The aircon clutch is not engaging when the a/c switch is pressed in the cab. It engages when I jump the relay, so it should work. It's gassed up OK. I've been told to check the "aircon low high pressure switch" since this can stop working so car thinks it has low pressure when it doesn't, not allowing the clutch to engage. But ... i think there may be two of them (low high) and in any case I can't locate it. Does someone know whereabouts it is please? Thanks