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AC issues

Discussion in 'HVAC' started by wayne swisher, Jun 29, 2021.

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  1. wayne swisher, Jun 29, 2021
    #1
    wayne swisher

    wayne swisher New Member

    Joined:
    Feb 24, 2021
    Messages:
    8
    Location:
    Missouri
    We are new to this so here we go... New to us this spring C40. Everything surveyed fine and worked flawlessly during the couple of weeks were able to enjoy the boat when first purchased. Now we can't seem to get things to cool down below 78 degrees. The boat was maintained during our absence (8 weeks or so) including system flushes (Barnacle Buster)

    Recent history, we had the boat out of the water for a couple of weeks for bottom paint and other repairs. Had HPF message in master shortly after splash down. Tech found what must have been a very clogged line (1 of 3). The other two seemed to be at full stream. After two unsuccessful Barnacle Buster flushes, an acid flush opened up #3 so all three units were flowing enough to consistently provide 78 at night and 80 degrees-ish during the day (Sarasota area day time temps 90ish).

    Within a week the master unit outflow stream looked to be about half of what appeared to be full streams out of the other two. However, it kept up with the temps as stated with no HPF. Asking around I'm consistently hearing "something isn't right, you should be able to get much lower room temps even in FL." I leave the units running 100% of the time and by generator when cruising or on anchor. I was told that is necessary in FL due to the growth issues.

    Today same tech says he thinks I need to replace the AC water pump as the current one seems to be not pushing enough water through the system. He supported this with stating the unit felt very hot to the touch and the impeller looked very warn. I'm a rookie but this seems plausible, yet odd that only one of the streams is showing weakness. He thought barnacles or some other debris may have made its way into the pump to cause problems. Wouldn't a weak pump essentially provide weak flow relatively equally? His response was the extra distance the water had to travel up and back to the master made it more susceptible to low flow issues. My BS meter kicked in on that one. Hope I’m wrong. I noticed that the factory AC pump is rated for systems up to 23K BTU. We have 26K BTU total.

    We already have some real money in the previous “fix” earlier this month and hope to get it right once and for all. Your input is greatly appreciated.

    System description:
    "High Velocity" System
    single 8,000 BTU unit
    two 9,000 BTU units
    Current pump capacity is “985 GPH at 3 ft Head”

    Questions:
    Is 78 degrees all we should expect in this heat? We keep the shades up on the direct sun side.
    Is it really necessary to run the AC 100% of time to prevent growth from getting started? Seems silly to be running the gen when cruising and we’re up top.
    Is more GPH the really the answer?
    Knowing more is not necessarily better, how much addition GPH do I consider upping the game if a replacement is in order?
    fyi - the "fix" earlier this month included the flushes and replacement of the strainer.
  2. Pascal, Jun 29, 2021
    #2
    Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    8,149
    Location:
    Miami, FL
    One issue we have here in so do especially after a haul out is a bunch of small white mussel like shells dying in the lines and manifold then Clogging everything. They usually collect at fittings either in the manifold, or at the unit inlets. Descaling helps but doesn’t always work as you need the solution to flow thru these blocks. If your tech ran the descaling thru all the units you may have had flow returning from only one or two units not all three

    the solution is to pull hoses and check them. You can also back flush them in a bucket using dock water. Just make sure you do it in a way that you are not back flushing the dead shells from one system to the next hence the recommendation to use a bucket to catch the stuff

    Blowing thru sections of hoses and coils can tell you where the issue is and if it’s cleared. If you have one pump for multiple units, the manifold can clog up easily as well

    the pump could be an issue too. What kind of pump do you have? Metal impeller pump suffer from impeller erosion with time and loose flow. On smaller systems like yours I like March pumps because you can easily pop the cover to check or replace the hard plastic impeller. A larger pump may help if the hose size matches but if you have blockages it won’t

    mans check the thru hull outside the boat. I ve seen cases where a plastic bag gets caught in the cover and then gets sucked in tight restricting the flow. When the pump turns off of HPF, the suction goes away and if you open the strainer flow looks ok. Till the pump starts again and the bag gets sucked against the cover...

    another thing to check is the temperature of the coils. They will be hot but you should be able to put your hand on them without getting burned. If one of them is significantly hotter than the others you know flow is restricted
    wayne swisher likes this.
  3. BigChief, Jun 30, 2021
    #3
    BigChief

    BigChief Member

    Joined:
    Sep 3, 2018
    Messages:
    81
    Location:
    CT
    Main ac problems in the Marine environment is Is the raw water cooling system blockages or bad water Circulating pumps. They cause the compressor to over heat and then shut down.

    The cooling side is based on freon, not enough freon and your temperatures might be low too much freon can cause damage to the compressor.

    As suggested check the raw water system make sure the lines strainer and coils are all clean of debris and build-up. Also check the air filter and make sure that you have sufficient air flow to the evaporator coils.
    Then get an AC guy the throw a set of gages on it and look at your pressure's to determine if you need freon.
    wayne swisher likes this.
  4. SplashFl, Jun 30, 2021
    #4
    SplashFl

    SplashFl Active Member

    Joined:
    Feb 2, 2021
    Messages:
    431
    Location:
    S. Florida _ Bertram 46
    As you're aware there are various causes for the failure of max cooling. Last time I had noticed a reduction of the water flow out the side it turned out to be some very small shell looking things that I can only assume in their earliest days passed through the stainless intake screen only to then grow just inside the valve. Probably never would have happened with more use.
    One of the AC related improvements I had made was a thin layer of insulation covered with fiberglass panels for the 3 front salon windows. Although cooling was a small part of why I had it done; the result eliminated the need to run both of the 2 AC units as the larger salon 18,000k unit also provided enough cooling for the two state rooms & the head while the smaller 12,000k unit remained off.
    wayne swisher likes this.