This article was updated on August 14, 2015. Original published on July 29, 2015.

The standards are designed to promote R744 for MAC and reduce initial system cost between HFC and HFO-based systems.

To date, DIN has published 16 standards including connection technology (DIN specification 74102), high-pressure refrigerant to coolant chiller (74103) and condenser/gas cooler (74104).

Pressure-limiting devices, evaporators and combined pressure and temperature sensors are all included in the list of standards while CO2 sensor technology and electric expansion valves are among four standards still under construction.

Department head of environment policy and technical environment protection, Stefan Wöhrl said the standards would have a positive impact on the CO2 MAC market.

“By specifying linear requirements and test procedures the standards will help to decrease the costs of air-conditioning systems, and guarantee basic quality, so that R744 systems can reach cost parity,” he said.

“It was difficult to develop the new specifications without the possibility to refer to an old list of standards but in this respect the work was very fast.”

The DIN Standards

The specification series ‘Road vehicles – R744 air-conditioning systems’ includes the standardisation of connecting components of R744 circuits for passenger cars, and the procedural requirements for their development and qualification so that the components can be used in the same or similar design in all R744 vehicle air conditioning systems.

Connection technology (74102): States that the minimum ensured lifetime of the component shall be 15 years, 300,000 km or 8,000 hours; notes the preferred material aluminum; covers the minimum/maximum component and ambient temperature guidelines as well as fitting diameters and pressure test results.

High pressure refrigerant to coolant (74103): With the same recommended minimum lifetime, the RC chiller (the coolant-to-refrigerant heat exchanger) should fit into the existing vehicle package. This specification states that refrigerant and coolant-side pressure losses should be kept to a minimum and the accumulation of oil in the RC chiller should be avoided. Detailed brazed-plate analysis is also included based on high-pressure tests.

Condenser/gas cooler (74104): States that a maximum of 30g of compressor lubricant shall be added, a maximum pressure of 17 MPa on the HP-side and a refrigerant operating temperature of (-5 to 165) °C for R744 units.

The other technical rules pertain to refrigerant lines and IHX in coaxial design, orifice with bypass (OTB), combined accumulator with internal thermal transmitter, serviceport, pressure limiting devices (PLD), accumulator-dryer-filter modules, back-pressure-valves, evaporators, shut off valves, mechanical coolant compressor, electric coolant compressor and combined pressure and temperature sensors.

R744 in MAC has been promoted by sections of the automotive industry, academics and environmentalists for its significantly lower greenhouse gas emissions (1,400 times less than HFC R134a), lower fuel consumption (25%) in bus and train MAC applications as well as significantly less service and maintenance to recover or dispose of excess refrigerant after repair.

The standards will be discussed at the International Motor Show (IAA) in Frankfurt from September 17 to 27.

The MAC issue has been a hot topic in Europe with automotive giants BMW, VW and Porsche all attending the event having taken positive stances on CO2 in the past.

There will be more to follow as more standards are released in the coming weeks and months.


IAA website
VDA website
DIN website

Author jamesranson