* German car makers have safety concerns
* EU has previously delayed enforcement of the law
BRUSSELS Feb 11 (Reuters) - The European Commission sees "no grounds" to give German vehicle makers more time to comply with EU law requiring a less polluting coolant to be used in vehicle air-conditioning, a letter seen by Reuters said, despite safety concerns.
From Jan. 1, EU law has demanded the phase-in of a refrigerant with a relatively low level of greenhouse gases, instead of a previous industry standard that has planet-warming power more than one thousand times that of carbon dioxide.
Only German manufacturers have raised objections to using the new coolant, which entails extra costs and which relates to all cars sold within the European Union.
A Daimler test last year involving a simulated leak resulted in the new coolant bursting into flames. Other German car makers have also voiced concerns about the new product.
Daimler said last month it had written to the Commission asking for a six-month grace period to find an alternative. On Monday, it said it had not received any official response.
The law has already been delayed to give manufacturers time to get a supply of the new coolant for a new generation of cars.
"We see no grounds to relaunch such a decision process," the letter from the Commission's industry department said. An EU source said the letter was sent to German authorities last week.
The letter asked for information on any new vehicles sold or registered after Jan. 1 that do not respect the new law and if so, what actions are taken to ensure conformity.
It also seeks more detail on the German authorities' safety concerns.
Last month, a Commission official, speaking on condition of anonymity, told Reuters that to try to reach a compromise solution the Germans had proposed penalties for car-makers that do not abide by the new law.
Daimler's test last year in which the new coolant burst into flames has triggered bitter exchanges between the German luxury automaker and Honeywell International Inc., which developed the coolant in partnership with Dupont and says it is safe.