The European Commission will mediate in a dispute over an air-conditioning refrigerant in Mercedes-Benz cars by refereeing safety tests.

The Commission said it wanted to guarantee the impartiality of an analysis of the refrigerant being carried out by Germany’s motor vehicle department KBA. It offered independent technical support for the investigation.

“The main objective will be reassuring manufacturers and the consumers that all means were invested to ensure the principles of objectivity and transparency in the risk assessments,” said a spokesman for Industry Commissioner Antonio Tajani.

Authorities in France have refused to register Mercedes A-class, B-class and CLA-class models built since mid-June because they use a refrigerant whose properties do not comply with a new EU directive on global warming.

Daimler has said its refusal to phase out the refrigerant R-134a is justified by safety concerns over the only available replacement, Honeywell International’s R1234yf.

Daimler late last year recalled all Mercedes-Benz cars worldwide that used 1234yf, saying that crash simulations showed it was more flammable than first believed.

The company says that, based on 2012 deliveries, the French block could affect about 2 percent of its global sales, or 29,000 cars.

Honeywell and its partner DuPont control the global supply of 1234yf which is forecast to rack up billions of dollars in sales.

The new EU directive says new cars must not use refrigerant with a global warming potential more than 150 times as great as that of carbon dioxide.

The old industry standard set the global warming potential at more than 1,000 times that of CO2, whereas Honeywell says its new product is only four times more potent.

KBA, the first official body to investigate the validity of Daimler’s claims, has been heavily criticized by both sides over the secrecy of its tests, whose results are expected in the coming days.

The Commission said results would only be published after a comparison was made between KBA’s results and those of previous industry studies that concluded risks were only minimal.