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.
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 to 30 °C (50 °F to 86 °F) higher than indicated on the pressure gauge.
Verification of Refrigerant in a Closed Reservoir
Refrigerant R1234yf is present in a closed reservoir or in a refrigerant circuit if the temperature indicator on the pressure gauge matches the refrigerant temperature (standing fluid adopts the ambient temperature).
A closed cylinder or a refrigerant circuit that has been switched off is empty when the temperature indicator on the pressure gauge is below the temperature of the refrigerant.
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.
The pressure of the refrigerant R1234yf and R134a are very close over a very large temperature range, they cannot be differentiated by a pressure measurement. Distinguishing is possible for example using a gas analysis. Refer to REFRIGERANT R1234YF ANALYSIS .