Overview
Before any refrigeration or air-conditioning system is put into service, a series of pre-operation checks must be completed to ensure safety, reliability, and regulatory compliance. These procedures — pressure testing, leak testing, evacuation, and charging — are examined in detail under EU Implementing Regulation 2015/2067 and form a core part of F-Gas Category I and II assessments.
Strength (Pressure) Testing
- A strength test verifies that the system can withstand pressures above its normal operating range without deformation or failure.
- The test is performed using dry oxygen-free nitrogen (OFN), never with refrigerant or compressed air (which contains moisture).
- Test pressures are determined by the equipment manufacturer or relevant standards (e.g., EN 378). The high side and low side of the system may require different test pressures.
- The system is pressurised and held for a defined period. A pressure drop indicates a leak.
Tightness (Leak) Testing
- After the strength test, a tightness test at a lower pressure confirms the system is leak-free at closer-to-operating conditions.
- A small amount of trace gas or refrigerant may be added alongside OFN to allow electronic leak detection.
- All joints, valves, and connections must be checked systematically.
Evacuation and Dehydration
- Evacuation removes air and non-condensable gases from the system using a vacuum pump.
- The system is pulled down to a deep vacuum, typically below 500 microns (0.5 mbar), to boil off residual moisture at ambient temperature.
- A standing vacuum test is then performed: the pump is valved off and the vacuum level is monitored. A rise in pressure suggests moisture or a leak.
- Triple evacuation (evacuate – break with OFN – evacuate – break with OFN – final evacuate) is recommended for systems that have been open for extended periods.
Charging the System
- Refrigerant must only be charged into a system that has passed all pressure, leak, and vacuum tests.
- Liquid charging into the high side (condenser/liquid line) is the standard method for blended refrigerants (e.g., R-410A) to avoid fractionation.
- The charge quantity must match the manufacturer’s specification and be recorded in the system logbook.
Documentation
Under EU F-Gas Regulation 517/2014, the operator must ensure that an installation record is completed, including refrigerant type, charge quantity, date, and the certificate number of the technician. This record must be retained for at least five years and made available to enforcement authorities on request.
Exam Tip: Understand why OFN is used instead of air or refrigerant for pressure testing. Know the correct order of operations — strength test, tightness test, evacuation, vacuum hold, then charge. Questions often present scenarios where steps are performed out of order or with incorrect gases.
