Volkswagen Golf 1999 Service Manual page 3911

A/C refrigerant system, servicing
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A/C refrigerant system, testing with
pressure gauges
Due to the constant temperature/pressure
relationship of refrigerant R-134a,
approximate high-side system temperature
can be determined based on system
pressure.
Pressure gauges may have one or more
temperature scales in addition to the
pressure scale. Since various refrigerants
have different temperature/pressure
relationships, each gauge is specific for a
particular refrigerant.
Measuring pressure and temperature in a
"switched-on" refrigerant system
Use the A/C refrigerant high-pressure gauge
to measure high pressure between the
compressor and restrictor (including
condenser) with the A/C switched on.
Use the A/C refrigerant low-pressure gauge
to measure low pressure between the
restrictor and the compressor inlet (including
evaporator) with the A/C switched on.
The temperature displays of the low- and
high-pressure gauges apply only to a portion
of the low- and high-pressure sides. The low-
pressure gauge displays approximate
temperature between the restrictor and
evaporator outlet. The high-pressure gauge
displays approximate temperature between
the compressor outlet and restrictor.
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13/2/2005