VW Golf manuals

Volkswagen Golf Service & Repair Manual: Test and measurement work that can be performed using a pressure gauge

Displays on the pressure gauge
1 -  Temperature scale for refrigerant R134a CF3–CH2F or CH2F–CF3.
2 -  Pressure scale
In addition to the pressure scale, the pressure gauges can have one or more temperature scales. The scale values for R134a are assigned according to the vapour pressure table. Because different refrigerants have different vapour pressures at the same temperature, each temperature scale is labelled for the respective refrigerant.
 

Test and measurement work that can be performed using a pressure gauge

Pressure gauges enable the following test and measurement work

a – Pressure and temperature measurement in the refrigerant circuit
The high-pressure gauge allows the pressure and temperature to be measured with the air conditioning system switched on irrespective of whether this is at the outlet of the air conditioner compressor through the condenser up to the restriction (restrictor or expansion valve).
The low-pressure gauge allows the pressure and temperature to be measured with the air conditioning system switched on irrespective of whether this is at the restriction (restrictor or expansion valve) through the evaporator up to the inlet to the air conditioner compressor.
  Note
The relationship between pressure and temperature shown on the pressure gauge is valid only where the refrigerant in the circuit is liquid or vapour, but not when it is gas. In the gaseous state, the temperature is approx. 10°C to 30°C higher than indicated on the pressure gauge.
b– Evidence of refrigerant in a closed container
Refrigerant R134a is present in a closed container or refrigerant circuit if the temperature indicated on the pressure gauge corresponds to the temperature of the refrigerant (the temperature of a standing liquid stabilises at ambient temperature).
A closed container or switched-off refrigerant circuit is empty if the temperature indicated on the pressure gauge is below the temperature of the refrigerant.
  Note
The dependency between pressure and temperature described on the pressure gauge no longer applies when there is no liquid and the pressure is created by gas alone.
Refrigerant circuit with restrictor and reservoir
Arrows show the direction of refrigerant flow. A- low-pressure side of the refrigerant circuit. B- high-pressure side of the refrigerant circuit.   ...

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