M9-26 Air Conditioning System 05/02 M09010
for HFC 134a Refrigerant
The moisture must turn to gas before the pump can pull
it out. The moisture takes time to boil away, so that it
can be drawn out of the system. The vacuum pump
can draw most of the air out quickly, but a deep vac-
uum requires more time; the deeper the vacuum the
more time required.
The most important factor is the ability for the sys-
tem to hold the deepest vacuum the pump can pull,
and hold it for 15 minutes after the pump has
stopped. This may take several tries depending on
how long the system was held in a vacuum.
Charging the AC System
When charging the system, it is possible to put it in as a
gas or as a liquid. Adding refrigerant as a liquid is
faster but can damage the compressor if not done cor-
rectly. The procedure used, and where the refrigerant
is added in the AC system makes a difference. When
using refrigerant as a liquid, never add more than two
thirds of system requirements as a liquid. Finish charg-
ing the system using gas.
The proper method for charging refrigerant into a R-
134a system is to first, recover all of the refrigerant
from the system. The charging refrigerant should then
be weighed on a scale to ensure the proper amount is
charged into the system. Most recovery units include a
scale within the apparatus, thus making it very easy to
charge the correct amount every time. If equipment
such as this is not available, a common scale can be
used to determine the weight of charge. Simply weigh
the charging tank, subtract the weight of the proper
charge, and charge the system until the difference is
shown on the scale. On certain types of equipment, it is
also possible to add any necessary lubricant when
charging the system.
If a scale is not used when charging R-134a into a sys-
tem, it is difficult to tell if the correct charge has been
achieved. The sight glass can provide some indication,
but it is not a reliable tool for determining proper
charge.
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