Diagnosis And Testing; Pressure Gauge, Tests And Measurements - Audi 100 1991 Repair Manual

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A2 2001 ➤ , A ...
Refrigerant R134a Servicing - Edition 01.2011
4

Diagnosis and Testing

⇒ "4.1 Pressure Gauge, Tests and Measurements", page 142
⇒ "4.2 Leak Detection", page 143
⇒ "4.3 Refrigerant Circuit Concerns", page 151
⇒ "4.4 Pressures, Checking", page 153
4.1 Pressure Gauge, Tests and Measure‐
ments
Indicators on pressure gauge
1 - Temperature scale for refrigerant R134a CF3–CH2F or
CH2F–CF3.
2 - Pressure scale
Note
Pressure is measured in different units: 1 MPa (mega Pascal)
corresponds to 10 bar positive pressure or 145 psi, 1 bar absolute
pressure corresponds to 0 bar positive pressure and thus to the
ambient pressure (atmospheric pressure).
The pressure gauge may have one or more temperature scales
next to the pressure scale. R134a scale values are allocated re‐
spectively in the vapor pressure table. Since various refrigerants
create different vapor pressures at the same temperature, each
temperature scale is identified for the respective refrigerant.
♦ The pressure gauges makes it possible to perform the follow‐
ing checks and measurements.
Pressure And Temperature Measurement At Refrigerant Circuit
♦ High pressure gauge measures pressure and temperature,
which expand uniformly from outlet of A/C compressor via the
condenser up to constriction (restrictor, or expansion valve)
with A/C system switched on.
♦ Low pressure gauge measures pressure and temperature,
which expand uniformly from constriction (restrictor, or expan‐
sion valve) via evaporator up to input of A/C compressor with
A/C system switched on.
Note
The relationship between pressure and temperature indicated on
the gauges only exists in a refrigerant circuit that contains liquid
or vapor, but not gas. In a gaseous state, the temperature is ap‐
proximately 10° C to 30° C higher than indicated on the gauge.
Verification Of Refrigerant In A Closed Vessel
Refrigerant R134a is present in a closed vessel or in a refrigerant
circuit when temperature indicator on the pressure gauge match‐
es the refrigerant temperature (standing fluid adopts the ambient
temperature).
A closed vessel or a refrigerant circuit which has been switched
off is empty when temperature indication on the pressure gauge
is below the temperature of the refrigerant.
142
Rep. Gr.00 - General, Technical Data
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