VW Polo manuals

Volkswagen Polo Service & Repair Manual: Pressure Gauge, Tests and Measurements

Indicators on pressure gauge
1 -  Temperature scale for refrigerant R134a CF3–CH2F or CH2F–CF3.
2 -  Pressure scale
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
a – 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 °C (50 °F) to 30 °C (86 °F) higher than indicated on the gauge.
b – Verification of refrigerant in a closed container
Refrigerant R134a is present in a closed vessel or in a refrigerant circuit when the temperature indicator on the gauge matches the refrigerant temperature (the temperature of standing fluid is equal to the outside temperature).
A closed vessel or a refrigerant circuit that has been switched off is empty when the temperature indicated on the 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.
 

Pressure Gauge, Tests and Measurements

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