34 www. refrigerationandaircon. co. za RACA Journal I March 2026
SOLUTIONS voices
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.
Stewart sent in the following: Hi Grant, can you please discuss the automotive side of air conditioning which is often overlooked. The compressors used seem to be different to the rest of industry. These small compressors use wobble plates for capacity control – could you explain how this works? Thank you.
Hi Stewart, yes the compressors used in the automotive sector are quite advanced units. They are for the most part open drive units utilising mechanical seals on the input shaft. There may be an electric clutch on the drive shaft depending on design but let us look into this.
There are various makes and types of compressors used in automotive air-conditioning systems operating on R134a and of late 1234yf. There is some movement into CO2, but this remains somewhat niche. In most cases the compressor internal design could be piston, scroll, wobble plate, variable stroke or vane. Regardless, all operate as the pump in the A / C system
to keep the refrigerant and lubricating oil circulating and to increase the refrigerant pressure from a low-pressure low-temperature vapour to a high-pressure hightemperature vapour.
Basically, all refrigeration compressors serve the same function in the system but how this is achieved differs widely. Let us look at the different types and their basic operation.
Scroll compressor.
Variable stroke compressor.
WOBBLE PLATE( FIXED TYPE) A reciprocating piston, fixed displacement compressor. The pistons are operated by a wobble plate, which moves them backwards and forwards in the cylinders. As the front shaft turns the wobble plate angle changes, causing the pistons to move in and out, pulling refrigerant vapour in through the suction side, compressing it and discharging this high-pressure vapour into the condenser.
All images supplied by Grant Laidlaw
34 www. refrigerationandaircon. co. za RACA Journal I March 2026