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Old 16-07-2017, 18:37   #1
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Refrigeration and Freezing

I have a Iso-Therm SP system with a Danfoss 50F compressor. The condenser is the SP type, which is has a tubing wrapped in a coil inside a thru-hull. The motion of the boat causes the seawater in the thru-hull to transfer the heat from the condenser tubing.

I have two boxes side-by-side for refrigeration in the galley--one is a top loader, the freezer, and the other a front loading refrigerator. Up to now, they system has been adequate: the freezer freezes things solid and the refrigerator hovers between 38-42F.

My problem: the freezer still keeps things frozen, but the refrigerator is in the upper 50's. As near as I can tell, I do not have a spill-over system whereby there is an opening between the freezer and the refrigerator for the colder air to circulate from the freezer to the refrigerator. Is it possible for one compressor to have two evaporators with a Y-valve in between? How does one compressor with (as far as I know) one evaporator do two boxes that are not connected by an opening to transfer the cold air?

Some might suspect low refrigerant, but on adding some, the compressor runs hot, as in real hot.
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Old 16-07-2017, 19:57   #2
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Re: Refrigeration and Freezing

As long as the condensor is big enough, that compressor can handle two evaporators.

At least Technautics' CoolBlue can, doesn't need water cooling either, much easier to maintain out in the boonies, great ongoing support from Rich as well.
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Old 16-07-2017, 20:36   #3
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Re: Refrigeration and Freezing

Refrigeration - Evaporator vs. Holding Plate
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Old 17-07-2017, 05:25   #4
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Re: Refrigeration and Freezing

Do you know the normal temperature in your freezer side? That would be a good reference point to start from . If that temperature has risen then the temperature in your fridge side will rise as well.
If so you may not be getting proper condensing from your sink drain condenser . For proper condenser performance you need to have water flow over the condenser and the condenser coils must be clean . The placement of the condenser in the drain make it very susceptible to fowling from grease build up over time . Take a good look at it and make sure that has not happened .

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Old 09-02-2019, 08:37   #5
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Re: Refrigeration and Freezing

Moody, Some spillover systems use the box divider's lower heat conductance and thermostat settings to control refrigerator area temperature. The difficulty with this method is when climate conditions change like colder weather compressor runs less often producing less bleed over into refrigerator box. To lower refrigerator temp set thermostat colder.

Compressor is very hot is a general term and these compressors without air cooling do run hot, it is best to operate them at less than 130 degrees F. Adding or tampering with refrigerant is a mistake without further investigation by amperage draw or operating frost covered areas.

I would guess the added of refrigerant was excessive for a cap tube system that holds three ounces by weight of refrigerant.
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Old 09-02-2019, 12:31   #6
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Re: Refrigeration and Freezing

Quote:
Originally Posted by Moody46CC View Post
I have a Iso-Therm SP system with a Danfoss 50F compressor. The condenser is the SP type, which is has a tubing wrapped in a coil inside a thru-hull. The motion of the boat causes the seawater in the thru-hull to transfer the heat from the condenser tubing.



I have two boxes side-by-side for refrigeration in the galley--one is a top loader, the freezer, and the other a front loading refrigerator. Up to now, they system has been adequate: the freezer freezes things solid and the refrigerator hovers between 38-42F.



My problem: the freezer still keeps things frozen, but the refrigerator is in the upper 50's. As near as I can tell, I do not have a spill-over system whereby there is an opening between the freezer and the refrigerator for the colder air to circulate from the freezer to the refrigerator. Is it possible for one compressor to have two evaporators with a Y-valve in between? How does one compressor with (as far as I know) one evaporator do two boxes that are not connected by an opening to transfer the cold air?



Some might suspect low refrigerant, but on adding some, the compressor runs hot, as in real hot.


First you need to determine if you have two evaporators, I suspect you do not cause they are pretty easy to spot.
Then if I were you I would cut a hole in the separator and install a small ball bearing computer fan and couple it to an inexpensive thermostat to turn it on and off.
My spill over temp was difficult to control until I did this, now it maintains 36f consistently, I set the thermostat fan temp on at 37 and off at 34.

Total cost was less than $20.
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Old 09-02-2019, 12:34   #7
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Re: Refrigeration and Freezing

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Originally Posted by john61ct View Post
As long as the condensor is big enough, that compressor can handle two evaporators.

At least Technautics' CoolBlue can, doesn't need water cooling either, much easier to maintain out in the boonies, great ongoing support from Rich as well.


Number of evaporators are irrelevant within a realistic number, size is what is relevant.
I think even if you oversized the evaporators or had too many, it would just mean that you would get little to no additional cooling from the additional ones.
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Old 09-02-2019, 13:48   #8
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Re: Refrigeration and Freezing

It is reasonable to believe that Isotherm does not use Expansion valves that allow use of mutable or eutectic plates. The first thing I would recommend is to avoid ideas of modification and follow Cold Ed marines suggestion of cleaning the SP condenser. Next verify refrigerant charge is correct. The correct refrigerant charge of SP system is around three ounces, 1/4 ounce is too much or 1/2 ounce over charge could cause loss of performance. If compressor temperature is exceeding 150 degrees F There may be five or more ounces in this system.

Non Destructive Testing should come before taking a shot gun theories approach.
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