Author Topic: Isotherm Refrigerator Cycles On/Off and Won't Cool  (Read 1073 times)

Rick McClain

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Isotherm Refrigerator Cycles On/Off and Won't Cool
« on: June 19, 2016, 01:20:21 PM »
Hi,
   My 12vdc Isotherm Refrigerator with Danfoss controller starts, runs for a minute or two, then shuts off, and restarts immediately, but won't cool at all. I don't know if this is important, but before I shut it down recently for a haul out, it was running almost constantly and cooling to 15 to 20 degrees in the middle of the compartment.
     There seems to be a sensor that is shutting it down, but I can't locate it and don't know why it would since the cooling water is flowing well and neither the pump or compressor gets hot to the touch, and both seem to be running.
     The unit is cooled with the fresh water in my tanks, and I can hear the water being returned to the tank. I've also removed the sacrificial zinc and allowed water to run out there, just to make sure the flow is good. I've removed all the wires entering the controller and re-inserted each one to clean them. The unit is getting 12.8v at the controller from my house bank that reads 12.96v while the unit runs, and it draws about 6.5 amps as both the compressor and water pump start up each time, but draws very little while it is running, not changing until it shuts down, then immediately restarts. There is some kind of 4 wire switch between the compressor and the pump, and since I had a spare, I put the new one in, but it made no difference. I've removed the thermostat from the circuitry, and that made no difference either.
    I think I almost forgot to mention the most important facts. A pressure/vacuum gauge installed on the low side reads 90 lb. when the unit is running, drops to 83 lb. when it shuts off and will not accept any refrigerant. Being a photographer, not a refrigeration specialist, I don't know what that is indicating, but it certainly seems wrong. It won't draw a vacuum at all.
      I've run out of ideas for a cure and am hoping some unlucky sole on the forum has had the same problem and can help me out with a solution.
      Thanks, Rick McClain on CSY44 Island Time.
« Last Edit: June 19, 2016, 02:12:23 PM by Rick McClain »
Most of what I've learned, I learned not through brilliance, but through persistence.

Chip

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Re: Isotherm Refrigerator Cycles On/Off and Won't Cool
« Reply #1 on: July 09, 2016, 09:31:03 AM »
The Danfoss controllers have a connection for an LED that blinks with an error code. The problem you are having sounds like a "motor stalled" alarm. This is a misnomer because the actual problem is a failure of the control board. I found that the hard start board was better than the regular board but subsequently switched that out for the newest generation because it is supposed to draw less power. There are online suppliers like rparts that can supply the board. Some also have the instruction sheet as a pdf which shows how to hook up an LED if your system doesn't have one.

Rick McClain

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Re: Isotherm Refrigerator Cycles On/Off and Won't Cool
« Reply #2 on: September 12, 2016, 10:55:11 AM »
     Chip was absolutely correct. It did, indeed, turn out to be the controller, not the more expensive compressor. Thank You! If it had been the compressor, not only is it much more expensive, but I'd have had to lease a slip so a repairman could work on the boat, and hired the repairman to come and replace the unit, then draw the vacuum and replace the refrigerant. I'm sure it would have run over $1000, maybe $1500 or more. Way expensive. As it was, all I needed to do was purchase a controller for about $150, unplug the old one and plug the new one in.
       I say only $150. If this same electronics had been in some toy at Walmart, it would have probably only cost about $25-$30.  ;D
Most of what I've learned, I learned not through brilliance, but through persistence.