Robinair 16910 ID Plus Refrigerant Identifier - Manual (Page 8)

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Unit Description
Air-Radicator Purging
When a refrigerant source has been determined to be pure (at least 98% by weight of
either R-12 or R-134a), the instrument automatically offers the air purging feature to the
user, should there be any air contamination. Continuous monitoring of the venting gas
stream to determine exact air concentrations controls the purging feature. Purging limits
can be set by the user between 2%–9% by weight to tailor the purge to specific needs. The
instrument controls all functions of the purging feature with no intervention by the user
required to complete the procedure. The user can halt or cancel this procedure at any time.
Control of the purge operation is achieved through direct measurements of refrigerant
concentration and is not dependent upon temperature or pressure measurements.
Existing technology in the vehicle air conditioning market typically uses both pressure
and temperature measurements to determine air concentration and to control the
purging procedure. Pressure-temperature technology is susceptible to errors induced by
refrigerant contamination and difficulties in obtaining precise temperature and pressure
measurements. This is due to the inability to account for rapid temperature and pressure
drops of the refrigerant during the purge procedure by temperature-pressure based
equipment or procedures. Temperature-pressure based technology commonly requires
the refrigerant source to come to a temperature-pressure equilibrium before purging can
begin. This process can take as long as eight to 24 hours.
With direct measurement of refrigerant concentrations, there is no need to wait for
a refrigerant source to reach a temperature and pressure equilibrium. Also, rapid
temperature and pressure changes during purging operations do not affect the
measurements.