CO2 (R744) listed as acceptable alternative for vehicle air conditioning

On June 6th 2012, the US Environmental Protection Agency (EPA) published a final rule in the Federal Register which modifies the EPA previous determination for R744 use as an alternative air conditioning refrigerant.

Under the EPA Significant New Alternatives Policy (SNAP) program, any alternative refrigerants for vehicle air conditioning must be approved. EPA will determine the refrigerant to be unacceptable,acceptable subject to use conditions or acceptable subject to narrowed use limits.

Previously the EPA determined CO2 (R744) to be ‘acceptable’. This final rule updates to ‘acceptable subject to use conditions’.

The following conditions have been set;

1. Engineering strategies and/or mitigation devices shall be incorporated
such that in the event of refrigerant leaks the resulting CO2 concentrations
do not exceed:
• The short term exposure level (STEL) of 3% or 30,000 ppm averaged
over 15 minutes in the passenger free space; and
• The ceiling limit of 4% or 40,000 ppm in the passenger breathing zone.

2. Vehicle manufacturers must keep records of the tests performed for
a minimum period of three years demonstrating that CO2 refrigerant
levels do not exceed the STEL of 3% averaged over 15 minutes in the
passenger free space, and the ceiling limit of 4% in the breathing zone.

3. The use of CO2 in MVAC systems must adhere to the standard conditions identified in SAE7 Standard J639 (2011 version) including:
• Installation of a high pressure system warning label;
• Installation of a compressor cut-off switch; 8 and
• Use of unique fittings with:
i. Outside diameter of 16.6 +0/¥0.2 mm (0.6535 +0/¥0.0078 inches) for the
MVAC low-side service port;
ii. Outside diameter of 18.1 +0/¥0.2 mm (0.7126 +0/¥0.0078 inches) for the
MVAC high-side service port; and
iii. Outside diameter of 20.955 +0/¥0.127 mm (0.825 +0/¥0.005
inches) and right-hand thread direction for CO2 refrigerant service containers.

Final Rule is effective from 6th August 2012.

More information about SNAP is located at


One thought on “CO2 (R744) listed as acceptable alternative for vehicle air conditioning

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