Volkswagen Passat 1995 Official Factory Repair Manual page 4188

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.
Page 26 of 35
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12/7/2004