Robinair 15434 - Manual (Page 6)

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To use the gas ballast feature...
Moisture from the A/C-R system that is carried into the pump as a vapor
tends to condense into a liquid and combine with the vacuum pump oil.
When moisture contaminates the pump oil, it reduces the pump’s ability
to reach its ultimate deep vacuum level.
The gas ballast valve purges a small amount of atmospheric air through
the exhaust chamber. This extra volume of air mixes with the vapor from
the refrigerant system to prevent condensation and to help exhaust
moisture in the form of vapor from the pump.
To use the gas ballast, start the pump and open the gas ballast valve until
the system has reached approximately 1000–3000 microns. Close the
valve to allow the pump to pull down to its ultimate vacuum level. The
gas ballast valve is located beside the handle, opposite the inlet fitting.
The gas ballast valve may be opened or closed at any time during pump
operation. It is fully open at two turns counterclockwise.
NOTE: Robinair recommends the use of a thermistor vacuum gauge to
most accurately measure vacuum levels.
Your pump is now ready to evacuate air conditioning and refrigeration
systems. Follow normal service procedures and the A/C-R manufac-
turer’s instructions for connections to the system.
CAUTION Before connecting your vacuum pump to an A/C-R system,
remove refrigerant from the system in an accepted manner
using an approved recovery unit. Damage to the pump may
occur if evacuation is started while the system is under high
pressure.