Replacement of warm air ducting SO40

[davidt]

Hi
I have recently purchased Sun Odyssey 40 2001, owners version with one aft cabin portside. I am new to this forum, I have found some threads relating to this subject , but no answers to this specific problem.
The warm air ducting has become coated internally with a substance similar to cardboard, this has separated in places and has clogged and obstructed the duct, sufficient to stop Webasto heater firing. The heater is located in aft starboard locker.
I started replacing the ducting with new, but the ducting behind the cooker and fridge is fixed and inaccessible. One post refers to this section as being factory installed, ie before galley cabinets were fixed.
I wish to avoid removing any cabinets if possible. Belatedly, I am wondering if the coating could have been removed with vacuum tool

Any ideas appreciated
David

[Trevor]

Hello davidt,

I have never heard of this problem. I assume the Webasto will not fire because it senses too much back pressure in the ducting? I would make sure that is the reason for the Webasto not firing by removing the duct on the Webasto outlet and seeing if it fires ok without the ducting in place.

If the ducting is faulty and needs replacing it is not the end of the world but is a slightly painful job. The section you refer to behind the galley is installed at the factory certainly on the SO36i and the SO42DS, both of which I have owned. I will assume the SO40 is the same.

It would be unusual for that section to be faulty as it is a genuine Webasto duct and I wouldn't think much could go wrong with it. Having said that, if I was asked to replace it I would join the new duct to the old and pull the new duct through the space behind the galley. Either that or I would simply push a smaller diameter duct up the centre of the existing 90mm duct and accept the slight reduction in flow.

Why don't you simply remove the duct from the outlets and run the system flat out to try to blow out the debris for a while and see how that works?

Regards,

Trevor

[davidt]

Hi Trevor

Thanks for your reply. The problem was identified by an engineer who came to service the heater as excessive back pressure. Clearly this is due to the sediment that has been deposited over the years suddenly becoming detached in places and blocking the ducting.
Unfortunately the same engineer started making a real mess of the ducting in the aft locker space, near the heater, so I stopped any further work. I had thought it would be a relatively easy task to do as you suggest, simply pull through a new section of ducting as I removed the original. Unfortunately the section behind the fridge and cooker is held in place , presumably by the same cable ties as used elsewhere for securing the ducting

Perhaps as you say the ducting could be blown through with a high pressure jet, I will pursue that idea.
Thanks again

David

[Trevor]

Hi David,

i just cannot imagine how that much sediment could gather to block the duct as it is 90mm diameter. It is a requirement of the Webasto installation instructions that the main saloon outlet not be able to be closed. All other outlets can be the type that can be closed but the main one in the saloon is an open vent to always allow reasonable flow. At least that is the case on the SO 42DS.

You could always use an inspection camera on the end of a flexible extension if you really wanted to see what was going on or simply push through a cylindrical brush of 90 mm diameter if you wanted to clean it out.

Regards,

Trevor

[dnickj]

Hi
Just a point of note the sediment you talk if in the duct is part of the construction which is formed of a foil outer and a paper/card type liner
Over time the I bed becomes brittle and can brake up which sounds like your problem
Mine has just started to go the same way on a 2003 boat so far I have just replaced the first meter from the heater but will probably have to do it all in the end I have found what looks to be a better duct made from silicone and neoprene which is much more durable



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[davidt]

Hi
That is a fascinating comment. I originally thought it was part of a lining, but when I purchased a new section to replace it, no similar lining was evident. Strange type of lining for a warm air duct, the new ducting appears just bare metal internally, no lining.

This suggests that removing the cardboard type lining, whether with vacuum or high pressure air is not the best solution. That brings me back to what technique exists to remove the section of ducting behind the cooker/fridge?

Thanks
David

[dnickj]

I did think on this that maybe an access could be cut in the timber work behind the stove if done neatly it should not be too obvious


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[Trevor]

I was digging around in the shed and found a couple of pieces of webasto ducting. I was wrong in saying the duct was 90mm in my earlier thread. It is actually 80mm inside diameter. The other ducting up the centre of the 80mm section in the photo is 60 mm inside diameter. You can see the cardboard lining up the centre of these pieces of duct.

The easiest fix for this problem (but obviously not the best fix) would be to push the smaller diameter duct up the centre of the original duct. I think it may be ok to use 75mm duct up the centre of the 80 mm existing duct. It would provide slightly more backpressure but it may be acceptable. I would think certainly more acceptable than having to get in behind the galley to replace the original piece.



I hope this helps,

Regards,

Trevor