Yes there is a switch in the low pressure line (sorry I don't have a picture). If you can't find it you can always put power to the compressor with a jumper wire from the battery.
Bottom right of the relay box (see picture).
Will need to jumper power to B(30)
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You should have power at 85. You can test this with a test light or meter. Then jump 85 to 30 to engage the clutch.