The R4 compressors don't have plugs, like the A6's do.
You'll need to remove the comp. and stand it on end to drain as much as you can out of it. You should turn the clutch every now and then to help move the oil out of the cylinders.
It doesn't have to be completely dry of oil. A small amount won't hurt. Just get as much as you can out of the comp., the evaporator, and the condenser. I assume you will be replacing the accumulator/dryer, if you have one?
('76 was the year they went from the VIR system to the orifice/accumulator, so you could have either system.)
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