Triple Evacuation Procedure for Moisture Removal

Moisture sources

Water in the system can come from a ruptured water-cooled condenser, leaks under vacuum pulling water vapor on the low side, or prolonged open to atmosphere.

Used when significant moisture is suspected; combines staged vacuum with dry nitrogen to boil off and purge moisture.
Optional brief compressor run can help dislodge water from oil (stir), but keep it short.

Step 1: Evacuate to 1{,}500\ \mu\text{m}.
Break vacuum with dry nitrogen at 2\ \text{PSIG} (start introducing nitrogen to mix with moisture).
Vacuum again to 1{,}500\ \mu\text{m} to remove moisture.
Optional: start the compressor briefly to dislodge water from the oil (only a few seconds).
Step 2: Break vacuum with nitrogen again and re-evacuate to 1{,}500\ \mu\text{m}.
Step 3: Final evacuation to 500\ \mu\text{m}.
If the system holds vacuum at 500\ \mu\text{m}, charge the system.
If not, continue pumping and waiting until a deep vacuum is held before charging.

Use a nitrogen regulator set to around 10\ \text{PSIG}.
Four-port manifold is ideal: one line to vacuum pump, one to nitrogen, with valves to switch between them.
Leave nitrogen connected; operate valves to alternate between breaking vacuum and introducing nitrogen as needed.
The nitrogen line should feed while the vacuum pump is active during the nitrogen-break steps.

Do not run the compressor while the system is in vacuum.
If used to stir out water from oil, run for only a few seconds and only when there is some pressure (from nitrogen).
After stirring, resume vacuum to remove moisture.