www. refrigerationandaircon. co. za RACA Journal I November 2025 35
Support
GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy( ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National Technical Diploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.
WELCOME TO THE SOLUTIONS PAGE
By Grant Laidlaw
Many people ask for assistance in understanding theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place.
Cayla asks: Grant, could you please look into the use of R744 and how these systems work. It is quite difficult to understand the operation of these systems. Also, a particular concern is the high pressures. Thank you.
Hi Cayla, yes I can help. In previous RACA issues we looked into CO2 as a refrigerant as well as the critical and triple point. We began looking at subcritical and transcritical systems and what is meant by these terms. Let us continue on this subject by looking at some of the servicing and maintenance aspects as well as explosion prevention.
INSTALLATION AND MAINTENANCE – TOOLING Normal refrigeration tools are used with the exception of:
Typical solenoid magnet.
In addition, you will need a digital charging scale suitable for the cylinder weight and sufficiently accurate. Solenoid magnets that are used to manually open solenoid valves, ensuring no refrigerant can be trapped in areas of the system. Trapped refrigerant can cause pressure build up and possible rupture of system components.
All images supplied by ACRA
Manifold set: 4-way-recommended 120 bars( 120MPa) – subcritical / transcritical, manifold gauge set with hose lines for CO2.
• Refrigerant transfer hoses 120 bar( 120MPa)
• CO2 gas detector as part of personal safety equipment
• CO2 leak detector as leak finding instrument
PRESSURE TESTING Dry nitrogen is used for the strength test with a suitable highpressure regulator. A suitable pressure regulator must be used. Failure to do so will result in injury or death. Be aware that there are risks associated with this, especially concerning the test of the high-pressure stage. The test is carried out with 1.43 × PS or with 1.1 × PS and a non-destructive test is executed at 10 % of all joints.
•‘ PS’ refers to the manufactured maximum system operating pressure.
• Pressurise slowly and hold pressure for at least 15 minutes.
• Ensure that there is adequate ventilation when releasing nitrogen pressure test charge.
www. refrigerationandaircon. co. za RACA Journal I November 2025 35