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Old 11-14-2017, 09:27 AM   #1
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Relay for air conditioning raw water pump?

I'm replacing a CruiseAir a/c unit with a new Dometic all-in-one, but keeping one CruiseAir system. Both old systems used the same raw water pump - either of them would activate the pump as they came on. They did this through an OLD CruiseAir relay box that is corroded to the point of needing replacement.
The question is, what do I replace it with? I need a relay that can have two 110V wires coming to it (two sets of wires - hot, neutral, ground), with one set of 110V wires coming out of it to power the pump. (In case it's not obvious, the new Dometic unit needs an external raw water pump, and has the connections to run 110V to the pump. If I had only this unit, I would run those wires directly to the pump.)
What is such a device called? Seems like it might be a common electrical gadget, but I don't know what to search for.
Thanks so much for any help!
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Old 11-14-2017, 10:12 AM   #2
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Had two MarineAIRRR/Dometic systems on my AT34. One was 12KBTU and one 16KBTU. Each unit passed through a "Pump Relay Panel" shown below. This is all I have - hope it helps in some way....

This looks like a new version of what I had: https://yachtaidmarine.com/shop/mari...SABEgLkP_D_BwE
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Old 11-14-2017, 11:04 AM   #3
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Not sure where you are, but I used Martin marine in Wilmington NC for replacement pump relays on my Cruiseair system. They had both the whole box or individual relays that went in it, or at least they did 4 years ago. (910) 799-9362. Good folks.
You might also try asking Depco Pump in Clearwater FL, they can point you in the right direction more than likely. (727) 446-1656
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Old 11-15-2017, 10:45 PM   #4
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You need two 120vac relays that have 120vac control input.

The control side (of each) is wired to the "switched" 120vac output of the ac units. The power "line" contact of both is wired to 120vac hot (same leg of 50 amp service), and the "load" output of both is wired to the pump in parallel.

That way either ac unit can energize the pump.

Now that said, depending on the ac units you may be able to simply wire the pump in parallel to each of the switched ac outputs of both units if they can handle the pump current AND.. are "switched" via internal relays on a control board or box.
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Old 11-16-2017, 12:38 AM   #5
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Quote:
Originally Posted by what_barnacles View Post
You need two 120vac relays that have 120vac control input.

The control side (of each) is wired to the "switched" 120vac output of the ac units. The power "line" contact of both is wired to 120vac hot (same leg of 50 amp service), and the "load" output of both is wired to the pump in parallel.

That way either ac unit can energize the pump.

Now that said, depending on the ac units you may be able to simply wire the pump in parallel to each of the switched ac outputs of both units if they can handle the pump current AND.. are "switched" via internal relays on a control board or box.
BEWARE of doing this if you have two power inlets on the boat and a split panel with an AC unit on each. You could be feeding 230 volts to direct short. That is why the relays exist.
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Old 11-17-2017, 08:37 AM   #6
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Beware of people that don't read or possibly fail to comprehend a post in their quest to save the day. Had my post been read it would be obvious that it is impossible to get 230vac from 120.
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Old 11-17-2017, 09:48 AM   #7
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Beware of people that don't read or possibly fail to comprehend a post in their quest to save the day. Had my post been read it would be obvious that it is impossible to get 230vac from 120.
And I was simply posting a warning about doing this with AC units on two different phased legs in case someone missed that in your instructions.
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Old 11-17-2017, 11:45 AM   #8
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Two 120Vac relays in a box can do the trick. Each coil fed from the respective AC unit, separate breaker for AC pump feeding the contacts.
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Old 11-17-2017, 12:56 PM   #9
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Yes, refrigeration relays work well 120v relays with 120v coils. I made one ten years ago that is working well to replace a relay box that had a bad board. I made the new box for less than a replacement board. Sometimes the old ways are better.
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Old 11-17-2017, 06:48 PM   #10
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And I was simply posting a warning about doing this with AC units on two different phased legs in case someone missed that in your instructions.
Yes I see that now. My apologies, now excuse me while I go heat up some crow while I look for that post comprehension book.
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Old 11-20-2017, 09:46 AM   #11
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Thanks for the input. We ended up buying a pump relay from Dometic that could handle 1, 2, or three a/c units. It was expensive (over $300), but works.

Interestingly, the original relay (from 1974) passed power from the a/c units through to the pump, but the new unit required a separate source of a/c power. Fortunately we had an available "Spare" breaker that was easy to use. Definitely a step backwards, technologically.
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Old 12-01-2017, 08:57 AM   #12
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Interestingly, the original relay (from 1974) passed power from the a/c units through to the pump, but the new unit required a separate source of a/c power. Fortunately we had an available "Spare" breaker that was easy to use. Definitely a step backwards, technologically.
Maybe not. You are no longer dependent on the ac unit supplying enough power to run the pump. Thats a plus.
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