Reroute Air Conditioning Vent

[harmony2]

We just took delivery of a new NC 895 with the blue hull.  We want to reroute the A/C from the small berth into the wheel house to improve the cooling up there.  I remember seeing a post from an owner who did this, but I cannot find it.  Please, anyone familiar with this modification please reply to this post or call.  Thank you!

Dick Brewer
[phone]

[scottyftlaud]

Did you have any success?  We also have an 895 Sport, in South Florida, thus the wheelhouse gets warm, while the lower cabins are nice and cool. The  AC does take the humidity out of the air, noticeably cooler than outside, but still stays warm. I was thinking of trying to cover 1/2 of the lower vents with cardboard, thus increasing flow above. We keep the AC running on shore power, and the generator while at sea.

Scotty

[harmony2]

Still no reply to my post except yours.  I did talk with a marine A/C specialist who is going to evaluate the problem on my boat next week.  He did tell me that there is an important reason that there is no way to close the vents.  These air conditioners must have the full unimpeded  air flow or the equipment will be damaged.  Don't cover any part of either of the vents in the staterooms.

[rene460]

Hi Harmony, as a sailboat owner without air conditioning, I can’t help much with how to re-route the a/c vents on your power boat, but perhaps I can help you understand a little about your air conditioning unit.  It’s worth understanding, as the same principles apply to your refrigeration unit, the only real difference being that one is optimised for cooling the inside of the food storage enclosure while the other is used to cool the air in the room.  You probably also have a/c units in your house and definitely refrigerators, which all depend on the same principles.

For a/c, there are two different air flows to consider.  One is the cool air inside the boat, the other is the warm air from the unit which carries the unwanted heat out of the boat and exhausts it to the outside.  This outside air must not be impeded, or the condenser will get too hot, the internal pressure will rise, the compressor will draw more current and eventually something will break.  The air does come from somewhere, probably inside the boat, though not necessarily, so the return air flow also must not be impeded, and as this air is exhausted from the boat, some ventilation air must also be allowed to flow freely in from the outside.  Alternatively your unit may be water cooled, either using a keel cooler or just a water cooled heat exchanger with a water pump drawing in cool water from a through hull valve, and discharging the warmed water through another.

The cooling air for your cabin also comes from the return air vent and returns to the cabin.  If the air flow is obstructed, the unit has less work to do, so it makes the air cooler.  What happens then depends on the control system built into your unit.  Does it have a thermostat that you can adjust?  Does it vary the compressor speed or just switch off?  Ask your refrigeration mechanic about this when he is on your boat.

Basically, if the unit keeps running, the air gets colder until the evaporator freezes up with ice formed from humidity in the air.  As water expands on freezing, this can damage the evaporator.  But it probably switches off on low temperature before this happens.

The result of all this is that it is difficult to see how re-running one of your outlet vents will damage anything, provided you retain a reasonable air flow.  However, finding a suitable route to run a sensible size duct from somewhere on the cool air side to where you want a new outlet usually presents a challenge in a boat, as a/c ducts are rarely an attractive feature.  So have a look around in cupboards and behind panels and see where you think it could run.  Then when your refrigeration mechanic comes, ask him about your proposed modification, or if he can make a better suggestion.  By starting with some understanding of what you are dealing with, you may get a more helpful response.

Rene460

[harmony2]

Rene460.

Thank you!  Very informative!

[bluedart]

sorry for delay in response.  i am the person who rerouted the A/C.  i only did the lower cabin to the main cabin since it was much simpler than diverting the front cabin.  since i don t use the lower cabin i just cut a hole in the a/c cabin and moved the duct work over several inches.  it did help.

eventually i want to reroute the forward cabin to the upper cabin by adding a divert able vent in the line feeding the forward cabin.  i would then be able to divert all air to upper cabin or leave the forward cabin open.

you can not just block vents.

next time i am on boat i will take pictures but if you look into your ac cabin you will see the various duct work and see how easy it is to move the lower cabin.  i hated to drill a hole in the fiberglass but it is fairly small. 

the forward cabin a/c runs along the port side of the lower cabin and is covered by a wood panel that is screwed in and also caulked.  a much larger job.  if i do this i will put the duct on the port side facing the helm chair.

i put the lower cabin duct on the same panel as the original a/c duct.  

[harmony2]

bluedart, thank you.  If I understand, you moved the vent over a few inches so it is now located under the table.  It's under the aft bench seat so both cabin A/C vents are blowing air forward in the same direction?

Harmony2  

[bluedart]

yes.  they are blowing the same direction.  it is not ideal and as mentioned for the rerouting of the front i plan to have the duct face the helm seat.

this was the simplest fix.  it does put more cool air in the cabin.  

[harmony2]

bluedart, I'm wondering about extending that lower cabin vent about 4 feet, putting a 90 degree elbow in and cutting a hole for the vent into the foot well under the table and having the A/C directed toward the helm??  There's plenty of room in the area between the lower vent and the port side of the cabin so it would be up and out of the way for accessing that cabin?

Harmony2

[scottyftlaud]

Thanks for all the info here. We will not impede any air movement. Given the newness of the boat, most likely have the dealers air conditioning person reroute the vents so as to not question the warranty, if any issue arise. Dealers can be somewhat picky in particular to off market home repairs. {{sigh}}

[Gio]

I will follow this post as i am studying a way to re-route the lower cabins flow on the pilot cabin. 

Can someone explain the technical reason why is not advisable to obstruct the lower vents? The A/C unit has a 1 fan and then the air is routed into a 3 ways air distributor, if you obstruct one shouldn't it increase the flow in the other two?

Very interested in this...

[scottyftlaud]

After the talk about rerouting AC vents, and the works it would seem to entail, we just placed a fan on the floor down by the lower berths, and aimed it upwards into the wheelhouse. That works nicely. Blows the cooler air from below upwards. This weekend, July 4th in South Florida with temps in the 90's and humid, the wheelhouse was a very comfortable 75.

[bluedart]

Hi,  How did you power the fan?  the only outlet i have is by the aft door.   i sure would not run an ungrounded cord to the bow to run a fan. Besides being sloppy , it is dangerous.    

i tried a fan power by the helm USB but the volume of air was weak.  

[paul075f200]

Hello, I do not own a nc895 (yet) but I would cut a air return in the common wall between the cabin under the floor and the pilothouse that could be closed when needed. That would allow cool air from the lower cabin to be returned easily through the pilot house.

[scottyftlaud]

I guess I should have added that we have a generator, and when we bought the boat we had extra outlets, and breakers, wired for both lower cabins (thinking in advance for microwave and small television usage). So it was just a matter of plugging in the fan.