What does zero PSIG represent in a refrigeration system?

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In a refrigeration system, zero PSIG (pounds per square inch gauge) is defined as the pressure measurement compared to atmospheric pressure. Therefore, when a gauge reads zero PSIG, it indicates that the pressure within the system is equal to atmospheric pressure, which is approximately 14.7 PSIA (pounds per square inch absolute) at sea level.

Understanding that PSIG measures pressure relative to the surrounding atmospheric pressure is critical. As such, a reading of zero PSIG does not imply the absence of pressure but rather indicates that the system's pressure exactly matches that of the atmosphere.

This concept is important in practical applications, as technicians use these readings to determine the operational state of the system, diagnose issues, and ensure that charges are within the correct operational ranges.