Brussels -- Honeywell International Inc. and DuPont Co., the largest U.S. chemicals company by market value, are being probed by European Union antitrust regulators over plans to produce a refrigerant for car air-conditioning systems. The European Commission said it opened antitrust proceedings into agreements between Honeywell and DuPont to produce the coolant. The regulator will also investigate whether Honeywell is abusing a monopoly position for the refrigerant and if it "engaged in deceptive conduct" when the low-emission product was endorsed by a car industry group, it said in an e- mailed statement today. Honeywell and DuPont are expecting growth from the technology they jointly developed to meet EU environmental rules to cut greenhouse gases from air-conditioning systems. DuPont told investors this week that the refrigerant promises "nice growth and some healthy margins." Honeywell's speciality chemicals division has said it expects coolants to help it make "extremely solid" profits. "The commission will examine the case as a matter of priority," the Brussels-based regulator said in the statement. "This investigation highlights the importance of ensuring" that agreements involving intellectual property "contribute to innovation rather than holding it back."