Can somebody describe how to do this?

All the A/C books I have seem to leave this detail out. I think my system may have all leaked out anyway, but I have no way of knowing. My A/C gauges are on the way from HF, but I want to disconnect my evaporator box tonight to replace stuff.

Original thread here...
W123 Testing the evaporator

Thanks,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car