Originally Posted by SV THIRD DAY
Insert primal scream here, as my 2-sentences left reply/question disappeared when I touched the screen
again after the admiral interrupted me 15 minutes earlier. I'll try again:
I hereby expose my refrigeration
lack-of-chops by wondering why it is that plate temperature matters at all, so long as the box stays the temperature you want/food stays frozen to the degree you desire.
In my previous life, I had a Frigoboat system which worked perfectly until it didn't work at all. It had two Carel electronic thermostats, both measuring box temperatures, and had 2° hysteresis, each.
The freezer thermo controlled the compressor, and the reefer thermo controlled the spillover fan. Both worked entirely perfectly, returning the box to the appropriate low temperature the moment the higher level had been exceeded. Indeed, unless the box was warm loaded, once it got to the desired temperature, it stayed in that range entirely reliably. I have no idea, and had no interest in learning
, what the evaporator plate temperature was during any of this. And, indeed, why it should be of interest to anyone is beyond me.
Enter, now, the replacement Sea Frost system which has a smart controller known as ET(T - apparently to distinguish itself from the other ET, with the expanding neck, which apparently was also smart). The plate temperature's cut-off point is relatively simple to set, but its actual temperature is buried deep in an arcane bunch of steps, further enhancing the thought that it is of interest only to refrigeration
geeks and not to actual users; the box temperature is what I see on the controller. Interestingly, despite the freezer's hysteresis being 6°, the box range - when it's mostly empty - works out to be right about 2°, just what I'd want.
My March Pump, which is located ~ 2' below the water line, fibrillates often, for reasons I'm not at all able to fathom; in a foul harbor, it's usually the intake line becoming packed with gunge, requiring a very convoluted sequence of disconnection and reaming in a contortionist position. Under way, there is no apparent reason, as the line is clear; the last couple of times it has been a matter of bleeding the pump at its output. It's again stuffed/howling (March Pumps are magnetically driven, need to be fully wet, and make nasty pre-failure noises if they aren't full of water), but as the engine
room was very hot, aside from gingerly clambering over the engine to reach the switch on the compressor box to turn it off, I've not resolved this particular stoppage/failure/whatever. As a side note, I can't begin to tell you how angry I am that a water system was included, instead of the immensely effective (it's all I had to dump heat in the Frigoboat system) keel cooler
. But I digress...
As there have been several instances over the last few days as we cruised from Fort Pierce to Charleston that the pump has been turned off until I can get to it again, I can tell you that the system is able to cycle even though the condenser is in a hot engine room and no water is helping to cool. And, I've seen the cutoff at 7° (box temp probe) a few times, even though it's usually much higher.
I started with a 10° cutoff, and moved down to 7° and then 5°, because...
The box is entirely full. The bottom 1/4 or so is water bottles both for space reduction and a thermal flywheel. The rest is, as desired for coldest to not-quite-as-cold, either up against the evaporator plates, in the middle, or up against the spillover divider.
Despite being right against the evaporator plates, hamburgers are firm but not hard frozen. Bread never gets frozen, anywhere. The hamburger buns come out very cold but not the least bit stiff. Having twice lowered the plate shutoff temperature (a 5°F difference) has not seemed to change matters.
Aside from the intense annoyance at having to rely on a pump which fails me as much as it helps, and plate temperatures (assuming that the probe is correct in its reporting to the computer) being in a range which should produce a box temperature well below freezing, of what use is the temperature of the evaporator plate? If the box isn't cold enough, run the compressor longer, until it IS cold enough.
Or at least it seems that way to me. In my Frigoboat system, with its box-only probe, I had it at 8-10° and it worked a treat, despite nobody, whether Carel or Frigoboat or me, having a clue as to what temperature the evaporator was.
Is there a reason I should care???
(My problems with this system are an entirely different matter and no amount of hair pulling by many competent folk, Rich included, have been able to make it behave any differently, nor explained why it shouldn't work perfectly.)