| Pressure gauges enable the following test and measurement work |
| a – Pressure and temperature measurement in the refrigerant circuit |
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| 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). |
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| 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. |
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