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Two Compressors, One Pump

Discussion in 'General Electronics Discussion' started by Chainplate, Aug 3, 2016.

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  1. Chainplate

    Chainplate

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    Aug 3, 2016
    I live on a sailboat that has two refrigeration compressors. The Freon is cooled by pumping sea water through a condenser. I recently hired a technician to do some maintenance and he removed both compressors to take to his shop for testing. Months passed. I began to get frantic and was getting nothing but excuses. Finally, with the threat of calling the cops, he returned my components - in a box. Luckily, I was able to find a good, reliable technician who could put everything back together and make it work. With the exception of getting the sea water pump to work regardless of which compressor was cycling.

    It sounds simple enough to me - just wire the leads from the control module on each compressor to the pump but that doesn't work and I don't know why. When it was working, there were three different relays used and for the life of me I can't remember how it was wired up. I'm very tired of drinking warm beer. Can anyone help me? Thanks!
     
  2. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Not enough information.
    Do you have a diagram?
     
  3. Chainplate

    Chainplate

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    Aug 3, 2016
    Sorry, I don't have a diagram. I wish I did.

    Each compressor has a terminal (labeled 'F') that outputs 12vdc when the compressor is cycling to drive a fan or pump (in my case, I use a pump). However, if I take the lead from terminal F on the refrigeration compressor and the lead from terminal F on the freezer compressor and connect it to the pump, one compressor will start the pump when the compressor is cycling but the other won't. I suppose this is why the original installer had three relays.

    I'm grateful that you've shown interest in my problem.
     
  4. LightShow

    LightShow

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    Jun 9, 2016
    What kind of control module is it? is it custom or is it "off the shelf"
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    If each compressor has a terminal labeled "F" there must also be a common terminal somewhere from which you measure 12 V DC from "F" to that common terminal. Connect the coil of a SPDT relay (the most common kind) that has a 12 V DC coil between "F" and the common terminal on each of the compressors (two relays). Wire the relay contacts in parallel so that if either relay is energized there will be continuity between the normally open and the moving contacts on the relays. Use this continuity to energize the coil of a third relay whose contacts close to turn on the seawater pump. This third relay will need a coil voltage appropriate to whatever voltage the pump motor uses, and you will get this voltage from whatever is powering the pump. You could get by with just the two relays, turning on the pump using the continuity that occurs when either or both relays operate.

    Perhaps you can post some happy-snaps of what you already have. Do you still have the original three relays? Are they all identical?
     
    Tha fios agaibh likes this.
  6. LightShow

    LightShow

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    Jun 9, 2016
    Im not A pump technician but if it hasnt been turned on in a few months wont it have to be primed?
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    Depends on the type of pump and whether it is above or below the supply.
    Being a boat it could be either.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Are you saying that the boxed parts returned to you by that turkey only included 2 relays but the system originally had 3 when he removed the compressors?

    BTW, I want you to know that if I were a Judge adjudicating that turkey I would award you pain & suffering. This would be on the grounds that being forced to drink warm beer is uncivilized, antisocial, abhorrent and exceedingly cruel! :eek: The only place on this earth that warm beer is acceptable is in a cooking pot containing hotdogs! :D

    Chris
     
    KeithM likes this.
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Chainplate, I forgot to ask you if the compressors were originally wired in an "OR" or an "AND" logic configuration? Restated, was this circuit configured to insure that both compressors would not be on simultaneously (OR) or did both compressors sometimes run at the same time (AND) if either thermostat happened to trip its relay?

    Chris
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
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    May 8, 2012
    This circuit will run the pump when either or both compressors are running. D1 & D2 are Diode Isolators. They're very common and inexpensive. The other Diodes are Back EMF Diodes. They should be integral to the relays and are shown enclosed in a box. In other words, they already exist (OEM) within the relay enclosure.

    Chris
    upload_2016-8-4_12-18-20.png
     
    hevans1944 likes this.
  11. Tha fios agaibh

    Tha fios agaibh

    2,173
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    Aug 11, 2014
    If your bored, Try a google search for mulled beer.

    Nice blocking diode circuit.
     
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