Don't forget that the compressor will ONLY work if the engine is running & the trans is in gear (well, you've effectively gotta be ryding it or nothing happens!!)

That 'Manual' warning will come up if the air bag pressure gets too low for whatever reason; if the compressor dies or stops working; or if the height & load sensing valving stops working.... it's basically a 'catch-all' warning for tghe ACS!

So you need to check all those things - the engine running bit is easiest; then having some air in the bag; & only then do you need to start getting worried about stuff having failed!

Good Luck!