There is no such thing as 'normal' pressure. The vent cap, depends on rating, will release the pressure to the overflow tank. So it will be never go over the cap rating. There is member who wants to measure the 'pressure' but I think it is a futile exercise.

If it feels soft overnight then do not worry about it. Have a beer and relax.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.