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Old 08-23-2015, 05:05 PM   #1
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Replacing 2 Marine air units with Webasto 16Ks

Bought two Webasto 16k RC H/A air conditioners, installing where 2 mermaid marine air unit are located. Re using the single 1000gph pump for seawater. I want to run the pump off of one or the other or both AC units. The pump relay from Webasto is over $250. and being a tightwad I want to see what other free thinkers say about the install and pump set up. I bought the new AC units for $2318. shipped free from IMarineusa

Thank you,
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Old 08-23-2015, 05:16 PM   #2
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Was there a relay from the old system, and could you continue to use it.
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Old 08-23-2015, 05:25 PM   #3
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2300 is pretty good for 2.
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Old 08-23-2015, 05:34 PM   #4
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No can't reuse the old controls and pump relay.

I am experienced with electrical systems and relays. I used to test and repair automotive computers and circuit boards. I just hate to pay that much for a couple of relays and a circuit I can build.
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Old 08-23-2015, 05:51 PM   #5
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Well, an electric junction box, and few relays, a terminal strip, and a few cable glands should do the trick. But I'd bet you'd end up with $50-$75 in parts before you were done, plus a big chunk of your time. I think it comes down to how you want to value and spend your time.
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Old 08-23-2015, 05:54 PM   #6
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That's a good price. Bought 3 of their 12k units last fall for around $3k from Imarine. Used the old pump controller for mine.

Think you need to either leave the pump on all the time or have each unit control it. Would seem pretty simple to wire one relay to do that. Take the pump circuit from one controller and run both wires through the normally closed contacts on the relay. Take the pump circuit wires from from the other controller and attach them to the normally open contacts and the relay coil. AC unit one comes on and power goes through the normally closed pair of contacts to the pump. AC unit two comes on and energizes the relay and powers the pump. Seems pretty simple to me, just maintain polarity continuity when wiring the relay.

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Old 08-23-2015, 06:04 PM   #7
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You might also call around to some of the bigger marine AC dealers and see if anyone has a used unit lying around. $50 might buy you a fully functioning relay bank.
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Old 08-23-2015, 07:30 PM   #8
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The fresh water pump for my a/c units come on when the breaker for the a/c is turned on and runs continuously. The a/c units cycle on and off with their own t-stats. Not sure this how I would have wired it myself but came that way and works fine.
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Old 08-23-2015, 08:39 PM   #9
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The fresh water pump for my a/c units come on when the breaker for the a/c is turned on and runs continuously. The a/c units cycle on and off with their own t-stats. Not sure this how I would have wired it myself but came that way and works fine.
Some are wired that way and some owners prefer it that way.

Others use a relay and triggers from the units...so when all the compressors shut down, so will the pump.

I prefer it with the pump shutting down.... as you can set the thermostats...and when the day warms or cools below your set...the system shuts down all the way.
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Old 08-23-2015, 09:36 PM   #10
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For years the raw water pump for marine A/Cs ran full time whether the compressors were on or not. And in many cases you just turned on/off the breaker for the pump to control it.

That is the cheapest, least complicated way to wire it.
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Old 08-24-2015, 08:11 AM   #11
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For years the raw water pump for marine A/Cs ran full time whether the compressors were on or not. And in many cases you just turned on/off the breaker for the pump to control it.

That is the cheapest, least complicated way to wire it.
Yup, that's what I did - nice and simple, less to go wrong. If you go with triggers, I suggest you fit a bypass switch. That way you can run the pump without the a/c's (maintenance etc) or when a trigger fails.
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Old 08-24-2015, 08:22 AM   #12
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All good advise! Thanks to all for another round of helpful information with out drama or BS

What a great forum for owners!
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Old 08-24-2015, 10:29 AM   #13
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Same issue. Bought two AC relays, controlled by the pump output of each A/C unit. Either relay when energized will run the pump. Mounted them in a plastic utility box and mounted a terminal strip on top to connect to pump power and the pump outputs from the A/C units. Probably less than $50. Could have added a switch to run the pump manually.
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Old 08-24-2015, 10:53 AM   #14
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Hi Bob, Thanks for the reply. Would one 5 pin relay have worked as well? Curious as to why two. Or do you have them wired to cancel each other?
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Old 08-24-2015, 12:21 PM   #15
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Hi Bob, Thanks for the reply. Would one 5 pin relay have worked as well? Curious as to why two. Or do you have them wired to cancel each other?
You need two relays. You cannot wired the two pump outputs from the two A/C units together, they may come come off different legs of the shore power and if the breaker was off on one unit you would be feeding it power from the other unit. One relay for each pump output. Either relay to run the common pump.
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Old 08-24-2015, 01:05 PM   #16
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BobH, thanks for the reply. Do you have a wiring diagram you could share? I am trying to understand how two relays, assume 4 pin ISO. Are used with out cancelling one another to break the circuit from the first unit on when the second is operated.
Thanks
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Old 08-24-2015, 01:10 PM   #17
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I'll look for a diagram, but it is really simple. Each relay will power the pump. At times they may both be energized, there is no reason for one to break the connection to the other one. This is of course assuming that the pump is driven by a separate power source. The pump outputs from the A/C units only energize the relays.
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Old 08-24-2015, 01:21 PM   #18
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Sorry, no diagram, I just put it together on the fly. Two 120 VAC relays with one NO contact on each. The coils are powered by the pump outputs on the A/C units. The two NO contacts are wired in parallel and supply power to the pump.
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Old 08-24-2015, 03:10 PM   #19
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Thanks Bob! Got it! I just had to draw it out and think for a moment. Lot going on today. Thank you for your help!
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Old 08-24-2015, 08:17 PM   #20
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do the coils heat soak when the pump shuts off at the same time as the compressor? Im thinking in terms of the solder or braze junction expanding and cracking.

With as much green sludge growing in my groco every couple of days I wouldnt mind easing up on the continuous duty.
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