We have enjoyed our 2018 640 from new, but about 2 years ago we noticed the top outer edges of the front panoramic window were warping up and letting daylight and eventually rainwater in. The age of the warping I think is significant, given what we have discovered to be the cause of the problem. Apparently Chausson advise not to close the inner blackout blind in direct sunlight with the panoramic window closed since the heat build up is sufficient to cause the warping we noticed. We reasoned that the combination of heat and air pressure within the double glazed cavity causes the problem.
The panoramic window is double glazed and very effectively (but importantly, not totally) sealed by two plastic bungs located near to the window mid-point twist lever clamps. We observed that the inner pane of the double glazed unit had bowed downwards into the cabin. When one of the bungs was removed there was an excessive and quite surprisingly a large loss of air pressure from the unit. I expected the inner pane then to resume its original concave shape, but the pane stayed relatively flat and the top edges of the panoramic window were consequently still not pulled back when the two top twist lever clamps were engaged. We realised that the flatness of the inner pane was preventing the unit from assuming the correct curvature.
I have noted others wrestling with this problem, trying to restore the original concavity to the inner panel by applying mecanical pressure to the inner pane. The problem is that the smooth uniform concave shape is difficult to achieve and maintain by applying only localised pressure across such a large area.
To solve this problem we applied suction from our quite powerful Vax cleaner to the hole in the unit where we had removed the bung and the inner pane immediately became concave. An excellent result, but as soon as the suction was removed the inner pane resumed its distorted flatness.
The effect of heat and air pressure had made the inner pane lose its originally manufactured concave shape and over about 3 years, air had seeped past the bungs and built up pressure within the unit over many abuse cycles, flattening the pane and causing the warping. We applied gentle heat (using a 1kw hot air gun) wafting it at some distance from the inner pane, then allowing it to cool while still applying suction to the unit. The results were much better, but some distortion was still apparent.
We repeated the process after moving the top twist lever clamps to the closed position with the window open, then closing the window over the centre clamps in their closed position causing the unit to assume a more curved shape. This finally restored the original shape to the unit that now fits as when new. We intend to repeat this process every couple of years to help maintain its shape.
One final addition could be to apply a UV sensitive film (that darkens in sunlight)to the outer surface of the window. This might help reduce the heat and air pressure changes that cause the problem. After all it would be useful to close both the blackout blinds and panoramic skylight to keep the interior cool.
The panoramic window is double glazed and very effectively (but importantly, not totally) sealed by two plastic bungs located near to the window mid-point twist lever clamps. We observed that the inner pane of the double glazed unit had bowed downwards into the cabin. When one of the bungs was removed there was an excessive and quite surprisingly a large loss of air pressure from the unit. I expected the inner pane then to resume its original concave shape, but the pane stayed relatively flat and the top edges of the panoramic window were consequently still not pulled back when the two top twist lever clamps were engaged. We realised that the flatness of the inner pane was preventing the unit from assuming the correct curvature.
I have noted others wrestling with this problem, trying to restore the original concavity to the inner panel by applying mecanical pressure to the inner pane. The problem is that the smooth uniform concave shape is difficult to achieve and maintain by applying only localised pressure across such a large area.
To solve this problem we applied suction from our quite powerful Vax cleaner to the hole in the unit where we had removed the bung and the inner pane immediately became concave. An excellent result, but as soon as the suction was removed the inner pane resumed its distorted flatness.
The effect of heat and air pressure had made the inner pane lose its originally manufactured concave shape and over about 3 years, air had seeped past the bungs and built up pressure within the unit over many abuse cycles, flattening the pane and causing the warping. We applied gentle heat (using a 1kw hot air gun) wafting it at some distance from the inner pane, then allowing it to cool while still applying suction to the unit. The results were much better, but some distortion was still apparent.
We repeated the process after moving the top twist lever clamps to the closed position with the window open, then closing the window over the centre clamps in their closed position causing the unit to assume a more curved shape. This finally restored the original shape to the unit that now fits as when new. We intend to repeat this process every couple of years to help maintain its shape.
One final addition could be to apply a UV sensitive film (that darkens in sunlight)to the outer surface of the window. This might help reduce the heat and air pressure changes that cause the problem. After all it would be useful to close both the blackout blinds and panoramic skylight to keep the interior cool.
