Audi A4: Pressure Gauge, Tests and Measurements
General Information
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 (145 psi) corresponds to 10 bar (145 psi) positive pressure. 1 bar (14.5 psi) absolute pressure corresponds to 0 bar/psi 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. The R134a scale values are allocated respectively 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.
Pressure Gauge Uses
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 expansion 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 approximately 10 ºC to 30 ºC (50 ºF to 86 ºF) higher than indicated on the gauge.
Verification of Refrigerant in a Closed Container
Refrigerant R134a is present in a closed container or in a refrigerant circuit when temperature indicator on the pressure gauge matches the refrigerant temperature (standing fluid adopts the ambient temperature).
A closed container 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.
Note
The relationship between pressure and temperature indicated on the gauges no longer applies if no liquid is present and the pressure is built up solely by gas.
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General Information
Note
The laws and regulations listed below are applicable in
Germany. Different or additional laws and regulations may apply
in other countries.
The effects of climate change can be seen wor
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General, Technical data
Safety Precautions
Safety Precautions when Working on Vehicles with Start/Stop System
There is a risk of injury due to the engine starting
unexpectedly.
The engine can start unexpectedly on vehicles with an
activated Start/Stop System. A message in the instrument cluster
indicates whether the Sta
Hydraulic Pressure Sensor 1 -G545- and Hydraulic Pressure Sensor 2 -G546-,
Removing and Installing
Note
The Mechatronic remains installed.
WARNING
The system is under pressure.
The electronic ATF pump must be deactivated every
time before opening the transmission, and the hydraulic
pressure reservoir is drained.
Refer to
→ Chapter "ATF Pump, Deactivating and Draining
