In another forum I visit…I answered a post http://www.boatered.com/forum/….._ID=130856 from a gentleman that was considering replacing his 12v standard plate system with a like system utilizing a Hold Over/Cold Plate in his factory (boat builder) built top loading box…The system he was considering is one of the package type systems offered today, and below is a copy of my post of considerations…(I had linked to my previous article here on Marine-AC)  http://marine-ac.com/2009/03/1…..igeration/

Let me say first that I'm not against holding plate systems but…Some of the points I'm trying to make in the article are…

Holding plates are a much different animal…In order to get the performance/temp desired, and holding time at that temp…Many factors come into play such as insulation, size of box vs size of plate, door seals, top or bottom loading, plate solution temp etc…

A holding plate systems main design purpose is to keep a given box at a desired temp for a period of time, without running the refrigeration unit to keep it there for that period of time…

Basically…The temp of the box while running the unit has little to do with how a holding plate system was intended to be used…and given two plates of the same size (area used in the box) a holding plate will not offer anywhere near the BTU of heat absorption that a standard plate will offer…

• Running…Plate for Plate, a holding plate needs to be much larger to do that same job of heat absorption.
• A typical 134a standard plate system will run that plate surface at -10 F.
• A 134a holding plate system can run the tubing inside the plate…and solution (liquid) at that same -10 F….But the solution is a limiting factor in some ways…
• 134a system plate liquid is typically mixed to change states from a liquid to a solid somewhere between 0 F. to 26 F. Depending on if the plate was meant for a freezer or refrigerator box…
• It is also a larger mass to change the temp of, so running it down to -10 as you might imagine takes more time & energy…and Likely never getting the surface of the plate quite down to -10 F.

If a holding plate/box is not designed/sized as such (To hold a desired box temp when off) it can be much less efficient than a standard plate system that can recover the box temp much faster and may provide for less overall run time in a 24 hr period.

As you see…It's hard to explain, but installing just any holding plate into a box because it will fit is almost never the answer to the most efficient or ideal box.

Holding plates can be over sized too, and thus undesirable if they keep the box too cold during that hold over period…Freezing lettuce etc…

What I'm saying is…A Hold over plate can and will continue cooling long after the t-stat has cycled the unit off if it has been run long enough to freeze the solution in the plate…and If it is enough BTU to compensate for the amount of heat leaking into the box…
If Not…Then you will need to run it longer to attain the desired temp in that box…
The thing is it will warm very rapidly back up to the point that the solution begins to thaw…and This is where the holding period is (during the thaw, or change of states of the solution) and the box temp during that period is related to all the factors I discussed.

If that holding period box temp is not what is desired…Then a holding plate has not gained you a thing…It has hindered things somewhat.

Am I making sense ?

The OP responded that I had…So I felt it might help here also…

Steve~

Read original blog post

Hello Steve,

I followed your advice last fall and had my existing unit repaired.  But since then, the boat has only been in mild weather.  I watched my thermometer in the evaporator cool down to the mid-teens, and then warm up to the mid to upper 20s and repeat the process over and over again.  But now we're in the Bahamas and it's rather toasty.  The compressor is running almost non-stop.  The temp in the evaporator is in the low to mid 20's.  Does that just sound like it's fighting the ambient or might there be too much or too little coolant in there?  I forget what you told me, is it supposed to only have around 4psi on the low side?  The unit is a Vitrifrigo ND35.

Thanks.

Kurt

Steve,

Sorry to hear Les has to act like that.  Since I made my suggestion that you hook up, I've learned a few things about him.  As you said, it's his forum, and that's fine.  But I can no longer recommend him to anyone and I refuse to purchance anything from him.  There are way too many other sources for such things.

As for your questions, I'm going to have to check on most of them.  I simply have a remote digital thermometer sitting in the evaporator.  So while not very scientific, it at least gives me an idea of what's going on.  It does frost up.  More on the bottom than the top, but it's there and it does freeze items.  It was in the upper teens last night, after the sun went down.  I'm starting to think what I need to do is get more cool air to the Vitrifrigo/Compressor itself.  It's about 5 feet away from the ice box and has plenty of room around it (like feet of room), but it does get warm out there in the forward port sponson.

Kurt

There actually is a pretty large hatch near the unit that is usually cracked open for a number of reasons.  I was just down in there and the temp isn't that bad yet today.  The repair last fall was to the filter, which had developed a leak.  I've got the low-side connection after the filter, but there is now a new connection before the filter.  Is that the high side?  I tried to test that and there was so much pressure I couldn't get my gauge on it.  I saw the needle over 100psi for sure while trying.  But after 3 attempts I gave up.  There were only 3 short bursts of leak from it while doing so, but that was enough to take the low side down to less that 2lbs.  I gave it a shot and the low is around 6 now (it sure doesn't take much!).

Does that tell you anything?

As you can tell, I know enough to be dangerous!

So the correct way to take the reading is to shut the system down for a bit and then connect?  But the system should be running after the connections are made to take the readings, right?