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Increasing A/C BTUs in a 278? 115 Degree Summers here!
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Author:  alanderson74 [ Mon Mar 04, 2019 12:32 am ]
Post subject:  Increasing A/C BTUs in a 278? 115 Degree Summers here!
Hi, currently my '08 278 has a 5000 BTU air conditioner, which works but can't keep up in the Arizona heat which is typically anywhere from 113-120 degrees at mid-day. I've done some research and have spoken to Dometic, Marinair and Cruisair but no one can tell me what the recommended BTUs for cooling in AZ's type of heat is.

I know its said that larger units may just end up frequently cycling on/off - but would that still apply in my case? Does anyone have experience with larger A/C units in really hot, hot weather?

Oh and also, my unit loses prime when reversing to anchor. I noticed the water hose has a slight dip in it which could cause lost prime, has anyone ever relocated the water hoses so that they are on a constant incline to the unit? Thanks in advance!
Author:  babbot1 [ Mon Mar 04, 2019 8:22 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
Our 258 had a 5000btu ac and it was not adequate on hot summer days in New England. You know the days you really want to use it. LOL.
I would call a marine AC guy in your area to help with sizing and the weather you guys get in AZ. I would think a 7500btu would be bare minimum on a 278. I would think a larger one should be fine, within reason, because you can always turn the fan down to reduce cycling.

If you are loosing prime you might have a tiny air hole in the line somewhere or the pickup on the hull could be pulling in air from a deformity or obstruction. Check that there are 2 hose clamps at every location and that they are tight and the hoses aren't old and brittle. Also check the sea strainer is lot leaking air.
Author:  alanderson74 [ Mon Mar 04, 2019 8:40 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
Thank you! The strainer is completely clean and tight, I will check the clamps and maybe replace the hoses - it would make sense that one is cracked somewhere from baking out in the heat LOL. By the pickup on the hull, do you mean that metal thru-hull water intake thing that directs water in from under the boat?

Losing prime has caused many frustrating weekends while trying to re-start the air conditioning. The only thing that seems to work to restore prime is to force water in from the A/C water outlet on the port side and then use (human) suction to get the water flowing again... :lol:
Author:  babbot1 [ Mon Mar 04, 2019 8:54 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
Yes, the pick up on the bottom of the hull where the water gets pulled in. It's possible if it got banged up or there is a lot of barnacle growth it could scoop the water when the boat is on plane and possible pulling the water out. Just a theory I have read, I have no experience with this happening.
Forcing the water in the way your doing it is the easiest way to prime. You can try wrapping a rag around the hose so you get a better seat on the thru hull.
Until you get everything fixed close the seacock before you leave the dock. That should hold the water in the lines. Just another thing to remember to do...
Author:  alanderson74 [ Mon Mar 04, 2019 9:01 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
What an awesome idea! I never even considered closing the sea cock to prevent air from getting in the lines! I will definitely try this - thanks for the suggestion!
Author:  acguy [ Mon Mar 04, 2019 12:52 pm ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
babbot1 wrote:
because you can always turn the fan down to reduce cycling.


Turning the fan down will not reduce cycling. It will actually drive the suction temperature down of the refrigerant which in turn will give you colder air or reduce the amount of airflow across the evaporator and start freezing the coil. A faster fan speed will do the opposite.

Is your sea water pump located below the waterline? if not relocate it. that will keep the system primed
Author:  alanderson74 [ Tue Mar 05, 2019 10:14 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
acguy wrote:
babbot1 wrote:
because you can always turn the fan down to reduce cycling.


Turning the fan down will not reduce cycling. It will actually drive the suction temperature down of the refrigerant which in turn will give you colder air or reduce the amount of airflow across the evaporator and start freezing the coil. A faster fan speed will do the opposite.

Is your sea water pump located below the waterline? if not relocate it. that will keep the system primed



I'll need to check, I currently have it pulled and working on removing oxidation and waxing :) Thank you for the suggestion!
Author:  alanderson74 [ Mon May 13, 2019 8:42 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
I accidentally stumbled on a solution to keep the A/C primed while reversing... Vacuum off the air intake grill that's attached to the A/C unit. While doing spring cleaning the air intake was cleaned, removing years of build up - haven't had a prime issue since - even while setting anchor. Just something to try if your are losing prime!
Author:  byron [ Tue May 14, 2019 6:35 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
I'm on Long Island and have a V-275. It came with a Dometic 8K unit which is sufficient for the area. In Arizona I would think more like 10K. Fan speed on Auto works out fine without icing of coils. When I first got the boat I had priming issues with the pump after the strainer, which is below the water line, I wound up adding a tee connection right after the strainer with a 1/2" boiler drain valve in it to let the air out only when I recommission the boat in the springtime. A small amount of air trapped anywhere in a hydronic system will drive you nuts for the whole season. Good luck.
Author:  alanderson74 [ Tue May 14, 2019 9:49 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
Thank you! I’ve got a quote on a 10BTU which I was considering... I’ll probably get it, worried about install though lol... thanks for your response!!!
Author:  byron [ Tue May 14, 2019 6:35 pm ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
My last boat was a Larson 260 which came with a 6K manual controlled unit. I changed it over to a digital unit. It was the first time I attempted this and it only took a couple of hours to swap over the entire system I purchased from West Marine. Once the 110 a.c. and through hull are in place, the rest is easy. As long as you have the room go for it, you will be rewarded in the heat of the summer.
Author:  firecadet613 [ Tue May 14, 2019 10:01 pm ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
alanderson74 wrote:
Thank you! I’ve got a quote on a 10BTU which I was considering... I’ll probably get it, worried about install though lol... thanks for your response!!!


I replaced the lackluster a/c on my '04 268. Was not a bad process, pretty easy to access it in the aft cabin. Had to take more of the boat apart to add an hvac vent in the v-berth. I did a quick search and can't find the thread.

Went from the stock 6BTUish unit to a 10+BTU. Got some of my money back when I sold the stock unit, it worked fine just didn't cool enough in my book. With the way the cabin door swings open, it sucks out a lot of the cool air. The sliding cabin door on my 318 didn't suck the air out when it was opened and I had no issues with the stock a/c unit on that boat. Typically kept the cabin at 70 degrees, the 268 just couldn't keep up while it was no issue on my 318.
Author:  chris268 [ Wed May 15, 2019 6:36 pm ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
alanderson74 wrote:
I accidentally stumbled on a solution to keep the A/C primed while reversing... Vacuum off the air intake grill that's attached to the A/C unit. While doing spring cleaning the air intake was cleaned, removing years of build up - haven't had a prime issue since - even while setting anchor. Just something to try if your are losing prime!


That should not of made a difference in losing prime, but it may help on cooling with better air flow
Author:  alanderson74 [ Thu May 16, 2019 8:41 am ]
Post subject:  Re: Increasing A/C BTUs in a 278? 115 Degree Summers here!
That's what I thought too, but for some reason it has worked over the last two weekends out. Could it be that more power is available for the A/C pump if te unit isn't struggling to breather?
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