air con anodes?

Nick_H

Nick_H

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I'm trying to do some preventative checks and maintenance prior to the summer trip, and it occurred to me that the air-con has a raw water cooling loop, and the compressor units must have heat exchangers, but I've never changed any anodes. Do they have them? It's a Dometic Cruisair system.
 
Nick_H said:
I'm trying to do some preventative checks and maintenance prior to the summer trip, and it occurred to me that the air-con has a raw water cooling loop, and the compressor units must have heat exchangers, but I've never changed any anodes. Do they have them? It's a Dometic Cruisair system.
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Strangely perhaps, there never seem to be any anodes on Dometic gear. My chillers don't have them afaik. The install manual says you can fit your own, in a T in the seawater circuit, but it is an odd comment because if you don't electrically connect it to the heat exchanger it won't be of any use. I've ignored it in 10 yrs+ of dometic chillers and never had a problem. These days I freshwater flush for 1/2 the year
 
I thought of it because I recently changed the anodes on the gyro heat exchanger, which need doing every 6 months as they fizz away before a year is up, so it does seem a bit strange that the air con doesn't have any. Still, I've not had any issues related to corrosion on the aircon, so I guess I'll just carry on as before.
 
Yup
Remember there is one in the genset heat ex too. Pencil anode, small thing. It's at the top of the vertical tube (kitchen roll liner size) that forms the heat ex, and annoyingly as the water level drops after you've used the genset the anode is left high and dry, while the lower part of your heat ex corrodes away! If you're thinking of preventative maintenance you are due a new heat exchanger soon - I reckon they last 7-8 years
 
If the heat exchanger has been made with Cupro Nickel tubing then it will suffer little from electrolytic corrosion, so won't need anodes. Sadly many cheaper makes use brass or copper, which will react adversely to other immersed metals in the marine environment hence the need for zincs to protect them.
 
There's a bit more than tube metal issues most marine are Cupro Nikel as superheat6K infers
Real issue is the impeller / pumps .
Self contained smaller may have nylon ,but bigger chiller /fan coil /centralised -will have a heavey duty pump with a bronze /brass impeller -which may need some form of anode .
Frigomar has an annual anode on the sea water in side near the pump .

Mase ( " mace"? ) generators -they are unique being air cooled .
The sea water does not touch the engine or the windings -it simply goes through a heat exchanger that looks like a car rad with a fan to blow cool air arround inside the box .
There is an anode on this ,but cheap if you forget and it corrodes away ( relatively to corroded engine / windings with direct cooled ) To change out .
As JFM infers for extended lay up ie winter of prolonged inactivity flush out the sea water .i used on a Fisher Panda Direct cooled auto antifreeze ( rust inhibitor qualities ) .depends on the seacock design -how easy it is to put it in and turning a blind eye to the enviroment at flush out .
Or just accept the anode works on the Mase radiator -so it's fine to leave in seawater like your stern gear .
New zinc as and when ?
 
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superheat6k said:
If the heat exchanger has been made with Cupro Nickel tubing then it will suffer little from electrolytic corrosion, so won't need anodes. Sadly many cheaper makes use brass or copper, which will react adversely to other immersed metals in the marine environment hence the need for zincs to protect them.
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Thanks Trevor, that's useful info, I'll do some digging.

On a related point, I also want to buy a spare raw water pump for the aircon to keep on board in case the existing one fails. I've identified that they are rebranded Oberdorfer pumps (with lots of boat added tax of course). It's an Oberdorfer model 104M, M stands for marine, but there are so many variants I'm not sure which one to go for. I can identify which motor I need and what capacity, but not sure if I need 416, 316 passivated, or Monel shaft, and also whether I need standard rubber seal or upgraded Viton or Teflon seal. It makes a big difference to the cost.

Anyone know what is normally required for continuous use sea water pumps?
 
Nick_H said:
Thanks Trevor, that's useful info, I'll do some digging.

On a related point, I also want to buy a spare raw water pump for the aircon to keep on board in case the existing one fails. I've identified that they are rebranded Oberdorfer pumps (with lots of boat added tax of course). It's an Oberdorfer model 104M, M stands for marine, but there are so many variants I'm not sure which one to go for. I can identify which motor I need and what capacity, but not sure if I need 416, 316 passivated, or Monel shaft, and also whether I need standard rubber seal or upgraded Viton or Teflon seal. It makes a big difference to the cost.

Anyone know what is normally required for continuous use sea water pumps?
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Is there an ID plate that shows the variant you have? After the model number there's usually letters/numbers that relate to the exact model variant.
 
I have the Crusair model P1500BXT, which seems to be unavailable now, but did retail around £1,000, and the Dometic replacements seem to be about the same. I can find lots of performance spec on it, but nothing about shaft and seal materials

As I say it's a re-badged Oberdorfer, which are available for £250-£600 depending on variant. I'm trying to work out if I need the extra cost of the 316 or Monel shaft, or upgraded seals. My guess is the standard seals will be OK, as the upgraded are for chemicals, solvents or high temperatures, but I'm not sure about shaft material for permanent immersion in saltwater.
 
aquapower said:
This is the spec sheet for that pump with all numbers listed.

www.oberdorferpumps.com/specificationsheets/1170
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Yes, I'd found that, thanks. What I can't work out is which materials are used on the current Crusair branded pump, so that I can replicate it on the Oberdorfer branded replacement. I wondered if there was an acknowledged best practice of which material to use for the shafts on these pumps for constant sea water use.
 
Excellent, thanks aquapower. I can't find that particular model for sale, it may be discontinued, but I have been able to identify it has a 316 shaft, which answers that question, so I can now find the correct pump from the current model range.
 
Viton and Teflon are trade names for seals made with PTFE as the critical ingredient. These will be self lubricating, whereas rubber won't be. If you are a high usage user then go for Viton of Teflon seals.
 
They corrode thru from inside so can catch you by surprise. They look ok ish from outside unless already weeping. It is at far left of genset as you look at the front, if yours is the 17.5kva which I think it is, and you have to remove the second front panel (with 10mm socket) to see it

A big failure would spoil a holiday. A more likely failure mode is that they weep, so you can bodge it for a few weeks. The 8 years thing is pretty accurate though, so you might want to buy a spare from ARE. Not big and not expensive. You'll surely need it end of this season
 
jfm said:
They corrode thru from inside so can catch you by surprise. They look ok ish from outside unless already weeping. It is at far left of genset as you look at the front, if yours is the 17.5kva which I think it is, and you have to remove the second front panel (with 10mm socket) to see it

A big failure would spoil a holiday. A more likely failure mode is that they weep, so you can bodge it for a few weeks. The 8 years thing is pretty accurate though, so you might want to buy a spare from ARE. Not big and not expensive. You'll surely need it end of this season
Click to expand...

Thanks for that
I will definitely have one as a spare for next year - if not sooner.
The boat is now getting to that age where these kind of things are needed to have as spares anyway.
We have a "lockup" in Spain where I used to keep spares but now I've started transferring kit onto the boat - just in case.
As you say, without a genset - we would be "stuffed" if we were planning to anchor for any length of time.
I'll get the manuals out and have a look at the part you are referring to.
Thanks for letting this thread drift.
 
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