Need a water flow switch to turn off cruisair AC compressor when water flow stops

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Jul 20, 2019.

  1. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    The way this compressor safety shutoff is designed uses a high pressure cut off switch with an automatic reset. It is bad idea since compressor will simply cycle on and off with Head PSI going to 400 psi if you have the unit set to run, and there is no cooling water flow.

    I was thinking a water flow switch in the outflow line coming from the condenser to the thru-hull so that when water flow stops, it disconnects the compressor, the off control could go in series with the pressure switch.

    Does anyone have an idea, link for a flow switch? Or another idea? I do have some big 3 pole contactor like relays with standard 120vac coils.
    The flow switch has to allow for the 5 gallons per minute typical water flow rate, that can not be restricted.

    in the photo, the high pressure cutoff switch is to the right. High pressure opens the compressor motor circuit. When pressure drops it turns back on. Newer marine AC do not auto reset this safety switch.
     

    Attached Files:

  2. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    I am thinking this air sensor switch, then coupled with a contactor.
    It turns on and off with adjustable WC of 0.1 to 10.
    Plumb it into the pump output at the pump.

    SUPCO NS2000031
    Sample Line Connector: Push-On Electrical Rating: 1/10 HP @ 120 to 277 VAC, 28 VA Pilot Duty @ 24 VAC, 125 VA Pilot
    Mounting Holes O.C. (In.): 3-5/32 Type: HVAC/General Purpose
    Item: Pressure Sensing Switch Agency Compliance: UL, CUL, CSA, CE
    Depth (In.): 1-1/2 Function: Sense Positive, Negative or Differential Air Pressure
    Application: Switching Based On Positive, Negative or Differential Air Pressur Mounting Location: Vertical or Horizontal
    Package Quantity: 1 Pressure Setting Range (In. WC): 0.10 to 10.0
    Height (In.): 3-1/4 Switch Type: SPDT
    MPN:
    NS2000031
    Features: Normally Closed Terminal, Normally Open Terminal and Common Terminal
    Operating Temp. Range (F): -40 to 190 Width (In.): 3-1/4
     
  3. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    20190728_125024.jpg Nope, that switch work on a vacuum.
    I bought an analog used washing machine water level switch. Has 3 levels with a handle. It works great, easily detects water flow, switch turns on with flow, off with zero flow. I set switch to middle position. PART# WH12X10065

    Plan to put the water level switch and relay in a Nema 3 watertight enclosure.
     
  4. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Today a hot day, I got it all hooked up and working perfectly.
    If water flow quits, the compressor turns off.
    I have the water level switch set to high water level.

    I have a little 12vdc computer fan for the water pump, I thought it might keep it cooler.
    I used a wall-wart to power the fan.
    Small red wire is the water pump on wire. It connects to the water level switch, wall-wart and the water pump.
    Small blue wire is for the heat pump reversing valve.
    Large purple wire is compressor hot
    Large white wire is compressor neutral.

    The water pump is actually a dishwasher drain pump.

    The entire circuit is gfci-afci breaker protected.
    For these setups, there is no ground wire back on the compressor, the copper tubing is the ground wire, on the evaporator there is a ground wire, as that is where the on -off and control switches are located. It is electrically grounded through the copper tubing. I used to wonder about that till I realized it.

    I am not totally done with this. I want to put a plastic cup over the water switch just in case it leaks. Was very nice that contactor had extra connections for joining wires.
    And nice that if you pry the metal edge, you can make the cover removeable on the electrical box.

    The main compressor wires, its just a yellow ring terminal secured in with the big set screw.
     

    Attached Files:


  5. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Spent the day on the water running the AC, it all worked fine whole time for hours. When I pulled away from dock and boat rocked over, water flow quit and compressor instantly turned off. Once the pump does that, it has to be turned off otherwise the water never flows again, so it works as expected keeping the compressor from shutting down on overloaded high pressure.

    Other nice thing, when the pump pumps water, when turned on, you hear an audible click of the contactor, which you then know water is flowing, you dont have to look.
     
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