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Having some aircon troubles on journeys longer than ~30 mins at a steady motorway speed whereby the level of cooling slowly gets less to the point there is no cooling at all. This is a major problem when even though it's nearly winter I still drove home tonight at 10pm and it was 29degrees. Once back doing stop start driving again I start to get cooler air again and after she's been stopped for a while then started again it's good old freezing cold air as normal.

Has anyone else suffered this and know what it might be?

One theory I have (no doubt way off) is that at motorway speeds the increased airflow plus some sort of sticking/broken thermostat (making the unit run constantly) is making the coolant freeze completely or at least some of it freeze and blocks the pipes. The aircon pipes on the left of the engine bay were covered in ice tonight when it happened and the rubber section of the right hand pipe was rock solid.

Any advice gratefully received as always.

It could be a blocked in line filter ... They are only £20 ..

Thanks Grizz. Been googling to try and get some more info on the inline filter but can't really find anything. Is it a DIY job or am I going to need a stealer or an indie to look at it?