This does sound like you have a feed pipe loose somewhere , more so as the floor and face vents work fine . But i'm gonna be honest here , i'm not exactly sure how much help , i'm actually gonna be . I only have very limited knowledge of the heater system , and that's totally due to my converting the radio socket to double din . This is made more difficult as my primary phone packed up 2 weeks ago , and the replacement does not have a camera . I didn't realise this when i ordered it , so is something else that needs addressing . I should also warn you , my van is a left hooker , however as no one else has posted , i will try and help .
Okay well , access to the heater is pretty poor with the dashboard in place . Basically the heater is mounted centrally , with the blower in the offside foot well , and the heater matrix on the nearside . What i believe is a collector box is mounted above the heater , and if you have the original donor vehicles dashboard fitted , can be accessed by removing the upper centre switch panel below the heater vents . Not that there's much point in doing such a thing , as interestingly the collector appears to be moulded as part of the dashboard top . On my van , a previous owner had cut a hole into this , to feed a gps wire and i ended up having to put it right , and plug the hole . I know for a fact the face vents are fed directly from this collector , and so would suspect this is where the feed for the windscreen is too . I'm unsure how the lower vent is supplied , logic dictates there must be some kind of bypass somewhere behind the heater , but this is surmised . Purely because there are none of the usual heater pipes you would expect to see . Instead the pipes are a moulded tube , more rectangular than round , probably to save space .
As it happens , my base vehicle is exactly the same year , and model as yours , however it's a coachbuilt Hymer . There are no heater out flow pipes within the engine space , only twin intakes from the space between the bumper , and front off side wheel . These feed into what appears to be , a filter box , of the type that probably housed a pollen filter at one time . It then passes through the firewall , i guess to directly feed the heater . Heat from the engine cooling system also passes through the fire wall beside this , to feed the heater matrix , towards the nearside of the heater box .
Now with all that said , this means the windshield feed , must actually be inside the vehicle somewhere , but is not visible , even when the lower dash panels are removed . Trust me , my van still has these panels removed , and i've just slipped out to check . I suspect it may feed behind a panel outboard of my dashboard , that i've not had to remove . But the truth here is , i don't even know if this panel can be removed , i've not had to access this area .
And so , that is pretty much it , however i would throw a caution in at this point . The 230 series has an electrical issue regarding the blower motor , in that prolonged use of the fourth fan speed , can melt the fuse , and damage the fuse block . It's actually a well known fault , and one i've had to deal with . The fuse block is no longer available , and took 3 years to source , eventually finding a used one from a breaker , in Lithuania .
