A/C compressor unit in Flybridge bonnet over salon?

I'm adding 16k Btu Reverse Cycle A/C to my Willard 36 sedan. Would be super convenient to place it right over the salon in a semi-dead space of the flybridge bonnet.

Has anyone done this? probably 9-foot lift from waterline. I see many larger pumps have a 20+ foot head rating, but wondering if this is practical?

Second question - adding e a smaller 6k Btu Reverse Cycle to the forward stateroom. Compressor unit would be about 3-feet above waterline. Given the difference in head/height and the difference in size, could I run both off the same water pump with an appropriate 2:1 switch panel?

Thanks in advance.

Peter

Know that the properly sized Dometic pump would handle the head pressure.
Would suggest that instead of splitting the cooling water supply you include a second pump for the additional unit. But that is from the Department of Redundancy Department. That way you have a completely separated system in case of a component failure. I just saw a larger boat where the loss of a water pump took 4 AC units off line.

Be sure you add additional isolators to factory vibration isolators in that overhead installation. Even with those support stanchions that salon overhead could become a drum very easily.

Also try and move the return grille as far as possible from the unit. This will reduce mechanical noise from the unit coming through the air return.

Keysdisease said:

Also try and move the return grille as far as possible from the unit. This will reduce mechanical noise from the unit coming through the air return.

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A question (which may be useful info to Weebles too): I imagine there is a prescribed size (i.e area) of return air for a given unit. Say 50 square inches or whatever it would specify.

How does that interact with how far away that opening can be? Any rule of thumb, or...?

One issue with it mounted there may be getting supply ductwork spaced out so that it doesn’t all come down in one spot. Is there room in the sides of the flybridge to put some supply ductwork in them so you can get cold air spread out in the salon? It will need to be insulated ductwork since it won’t be in a conditioned space. If it isn’t insulated you will loose a lot of cooling and the ductwork will get condensation on it which isn’t good either. It would be a good usage of the space if you can make it work.

Frosty said:

A question (which may be useful info to Weebles too): I imagine there is a prescribed size (i.e area) of return air for a given unit. Say 50 square inches or whatever it would specify.

How does that interact with how far away that opening can be? Any rule of thumb, or...?

Click to expand...

The installation instructions do give guidance for return vs supply placement. The return should be within 5-feet of at least one of the supply vents, which I suppose is to assure it is within the same room. Secondly, assure the supply does not point towards the return to assure there is no short-cycling of the unit.

Peter

I have an installation just like you describe. 16,500 BTU under the flybridge bonnet over the salon/galley. It began as a split unit with the compressor in the engine room and only an evaporator under the flybridge bonnet. I replaced the evaporator with a self contained Flagship marine unit. Some technical points + 1 on the vibration dampeners. My unit is in an accessible insulated plywood box to move air from a ceiling return to the evaporator. The discharge is two ducts to the interior of the boat. I solved the water supply by two LC-3CP-MD March pumps in series. Hoses took the place of the old refrigerant lines. Don't forget the condensate line. I have the old one that has never plugged but I also have a safety one that goes directly overboard should the old one get plugged. I have been very happy with this arrangement for several years in the hot Texas summers.

obthomas said:

I have an installation just like you describe. 16,500 BTU under the flybridge bonnet over the salon/galley. It began as a split unit with the compressor in the engine room and only an evaporator under the flybridge bonnet. I replaced the evaporator with a self contained Flagship marine unit. Some technical points + 1 on the vibration dampeners. My unit is in an accessible insulated plywood box to move air from a ceiling return to the evaporator. The discharge is two ducts to the interior of the boat. I solved the water supply by two LC-3CP-MD March pumps in series. Hoses took the place of the old refrigerant lines. Don't forget the condensate line. I have the old one that has never plugged but I also have a safety one that goes directly overboard should the old one get plugged. I have been very happy with this arrangement for several years in the hot Texas summers.

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Thanks. This is very helpful. Surprised about the March pumps in series. Was that a trial and error, or did you do that from the outset?

it was the plan. I am a mechanical engineer and pumps are my thing.

obthomas said:

it was the plan. I am a mechanical engineer and pumps are my thing.

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Great posts. I have been tempted to replace the split in my flybridge as you have done but the water pump was always the biggest issue. Self contained units are WAY more cost effective than split systems. Splits are nice to keep the noise and vibration in the ER but the cost 3,4,5x more than a comparable self contained unit.

More details....I after checking size I used the evaporator wiring for the entire unit; New unit only needed about 16 amps; ran pump wiring with the new water hoses. Pumps are plug into duplex receptacle controlled by AC. Ductwork is all insulated. I like Flagship because all control components are easy to find, cheap, and a household thermostat can be used. No $$$$ circuit board to replace. My unit has a 2KW heater coil so is not reverse cycle. Compressor does not run for heating. In six years now have replaced one relay.

I'd run separate pumps for the FB unit and the fwd unit. Check the head pressure of the pump you select. Good thing is it just needs enough head pressure to get up to the top of the hill, then once it flows back down to near WL a siphon should form and get flow rate to near if unit was close to WL. But the water must get up there with plenty of margin.

If you try to share pumps, flow will prefer the lower unit and might not get up to top of the hill.

I have this arrangement on my boat for the salon AC. CruiseAir system mounted in front of the FB helm. It needs some improving since the return is just a simple opening from the ceiling into the eyebrow area, then the cold air is ducted down into registers in the ceiling. There is also a smaller unit down under the floor to do the state room. A single centrifugal Dometic PML500L pump serves them both. That pump is supposed to handle a 14' head, it's probably close to that height. Besides the improvement needed for the ducting it works OK and there is plenty of cooling water flow for both systems. The only issue is the pump gets air locked and needs to be primed after it's been hauled. Another concern is the added weight from the AC unit up high but can't really comment how much that affect things.

lwarden said:

I have this arrangement on my boat for the salon AC. CruiseAir system mounted in front of the FB helm. It needs some improving since the return is just a simple opening from the ceiling into the eyebrow area, then the cold air is ducted down into registers in the ceiling. There is also a smaller unit down under the floor to do the state room. A single centrifugal Dometic PML500L pump serves them both. That pump is supposed to handle a 14' head, it's probably close to that height. Besides the improvement needed for the ducting it works OK and there is plenty of cooling water flow for both systems. The only issue is the pump gets air locked and needs to be primed after it's been hauled. Another concern is the added weight from the AC unit up high but can't really comment how much that affect things.

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This is helpful - thank you for info on single pump. I'm inclined to go dual pump but may try single first. BTW - my impression is having to prime-pump after haul happens on most boats. Probably not related to height of A/C unit in flybridge.

Peter

Yep, I've got one there too. Factory installed, just replaced it as it was 30 years old. Great location.

The Brockerts

mvweebles said:

I'm adding 16k Btu Reverse Cycle A/C to my Willard 36 sedan. Would be super convenient to place it right over the salon in a semi-dead space of the flybridge bonnet.

Has anyone done this? probably 9-foot lift from waterline. I see many larger pumps have a 20+ foot head rating, but wondering if this is practical?

Second question - adding e a smaller 6k Btu Reverse Cycle to the forward stateroom. Compressor unit would be about 3-feet above waterline. Given the difference in head/height and the difference in size, could I run both off the same water pump with an appropriate 2:1 switch panel?

Thanks in advance.

Peter

Click to expand...

We did this. We were lucky in that there was a space designed and plumbed for electric/water up on the flybridge next to the upper helm when the bought was built in 1997 for future AC.

We had a single 36000BTU unit from Ocean Breeze installed up in the cowl/brow above our pilothouse. We have 5 registers pumping air into the pilothouse/galley area and the return vent is up over above the stairs to the flybridge. I admit that it's quite a haul up from the intake down in the ER to the flybridge level and the pump that came with the unit wasn't getting it done. We replaced with a dometic pump and put in a bypass switch so that we could prime it because after times of infrequent use the unit would shut down and cycle due to no/low water flow before the pump could get the water up to the unit. It became a race condition. We are on our second season with it and the priming bypass switch works fine.

There is one final issue that I have to improve. On the hottest, muggiest of days we do get frosting/icing of the compressor which causes me to shut it down for a while to defrost. We had to wind the ducting from the return around up in the cowl a bit and I'm think that our routing might have introduced turns that decreased return air pressure. Another idea I had was that Ocean Breeze sells a control unit that has the ability to introduce a defrost cycle in so that defrost cycle would happen automatically.

HtH

-tozz

If the pump is routed to both the upper and lower it may not work for the upper

I plan to install a package unit under my pilothouse console. Right now I have the evaporator coil and blower there from a very old 16K split system. I also plan on a duct setup to use the new unit to air condition my pilothouse, right now I have tapped into the old unit ducts to partial cool and heat the pilothouse. My March pump will only need to lift about 14’ to supply the package unit.

mvweebles said:

[snip] BTW - my impression is having to prime-pump after haul happens on most boats. Probably not related to height of A/C unit in flybridge.

Peter

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*nod* I have to prime after haul out and also after extended periods of no usage.

-tozz

I have similar installation on my boat with a single pump serving all 3 a/c units, (one of which is as you intend to instal, others are in lower hull).Needs a valve on the outlet from the two lower units otherwise the water takes the easy route and none goes to the upper unit, easy to throttle while eyeballing the 3 overboard discharges until water comes out of all evenly, then it works fine. Needs the return to be ducted from saloon deckhead to the unit otherwise you are drawing from the large fb space not the cabin, all ducting needs to be lagged. Vibration issues, already mentioned how to fix these