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.
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.
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.