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Old 21-07-2019, 01:49   #1
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Fridge cycling frequently for very short periods

Our Isotherm self contained 90 litre fridge is constantly switching on and off. It runs for a few seconds then turns off then a few minutes later does the same thing. Occasionally it runs for a little longer. It is still keeping reasonably cold temperature but around 8 degrees instead of its usual 3 - 5 degrees.

Any suggestions? 8 degrees is way too warm for beer

TwT
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Old 21-07-2019, 06:32   #2
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Re: Fridge cycling frequently for very short periods

When my Seafrost unit acted that way it was moisture in the refrigerant. Changing out the filter/dryer, vacuuming the system to dry it out and recharge fixed it.
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Old 21-07-2019, 06:51   #3
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Re: Fridge cycling frequently for very short periods

Check that the heat exchanger on the back of your fridge is getting sufficient fresh air. If warm air gets trapped there the pump will run nearly continuously.
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Old 21-07-2019, 06:51   #4
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Re: Fridge cycling frequently for very short periods

Is it air cooled? 12/24VDc? if so, you might try disconnecting the fan for a minute to see if its overloading the module, when they fail they draw too many amps and the unit cycles off and resets.
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Old 21-07-2019, 07:34   #5
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Re: Fridge cycling frequently for very short periods

Have you checked Isotherms on line "Smart Energy Control Instruction and use Manual" ?
Dip switches may be set incorrectly.

Temperature probes may be incorrectly located stopping compressor too quickly.

Does the same condition exist when manual over ride switch is in manual position?

Moisture in refrigerant is unlikely if no one has tampered with refrigerant loop.

To isolate refrigeration away from an electrical control problem Connecting Danfoss control modules C and T together will run compress continuously and drop temperature to zero if it is a control problem and not a refrigerant problem.
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Old 21-07-2019, 08:48   #6
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Re: Fridge cycling frequently for very short periods

I agree with the response that you should isolate the problem. Jump out temp control and if unit runs properly, replace control. No sense opening a sealed refrigeration unit if not necessary.
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Old 21-07-2019, 09:01   #7
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Re: Fridge cycling frequently for very short periods

Check voltage at fridge. Short cycling like this is often caused by low voltage during compresspr start surge.
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Old 21-07-2019, 09:05   #8
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Re: Fridge cycling frequently for very short periods

I had a similar experience with Frigoboat. Voltage drop at compressor entry was the reason. Cleaning and re-connecting helped. The hint came from the distributor Coastal Climate Control after I sent them a short video I took with my phone showing the actual problem.
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Old 21-07-2019, 09:15   #9
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Re: Fridge cycling frequently for very short periods

Quote:
Originally Posted by belizesailor View Post
Check voltage at fridge. Short cycling like this is often caused by low voltage during compresspr start surge.

I've found with a low voltage problem the compressor will kick off on overload . It will not cool the fridge but instead will not start. Short cycling will also cause the overload to cut of power to compressor and again it will not cool down the fridge. Probably bad control.
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Old 21-07-2019, 09:34   #10
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Re: Fridge cycling frequently for very short periods

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Originally Posted by icemate View Post
I've found with a low voltage problem the compressor will kick off on overload . It will not cool the fridge but instead will not start. Short cycling will also cause the overload to cut of power to compressor and again it will not cool down the fridge. Probably bad control.
Bypassing all Isotherm's control over BD compressor as I recommended is first step. Should that not allow compressor to run next step would be to bypass all wiring from a fully charged battery direct to Danfoss module.
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Old 21-07-2019, 09:58   #11
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Re: Fridge cycling frequently for very short periods

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Originally Posted by icemate View Post
I've found with a low voltage problem the compressor will kick off on overload . It will not cool the fridge but instead will not start. Short cycling will also cause the overload to cut of power to compressor and again it will not cool down the fridge. Probably bad control.
Logical. However, boat is not stationary and if the cause is lose contact or old wire falling apart it is possible that fridge starts to cool and once boat moves the voltage drop comes and goes.
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Old 21-07-2019, 10:20   #12
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Re: Fridge cycling frequently for very short periods

also one more small point: minor intermittent voltage drop become more apparent into battery bunk discharge cycle when batteries are weaker and not able to compensate as when the bunk is charged or when under power.
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Old 21-07-2019, 14:51   #13
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Re: Fridge cycling frequently for very short periods

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Originally Posted by belizesailor View Post
Check voltage at fridge. Short cycling like this is often caused by low voltage during compresspr start surge.
I would not be surprised if this is your problem. Low voltage burns up more gear than high, ever did. Low voltage causes an over heat, thermal couple shuts it down, couple minutes it cools some, closes circuit, and it starts over again. Insure that you have a minimum of 12 - 12.2 volts, most dc compressors need 12.4- 12.6 to operate efficiently. Be sure and check that voltage on start up and first 15 seconds of running. You may have a burned or corroded connection, no load it will show proper voltage, but looses it under load. Hope this helped.... CaptVR
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Old 21-07-2019, 16:48   #14
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Re: Fridge cycling frequently for very short periods

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I would not be surprised if this is your problem. Low voltage burns up more gear than high, ever did. Low voltage causes an over heat, thermal couple shuts it down, couple minutes it cools some, closes circuit, and it starts over again. Insure that you have a minimum of 12 - 12.2 volts, most dc compressors need 12.4- 12.6 to operate efficiently. Be sure and check that voltage on start up and first 15 seconds of running. You may have a burned or corroded connection, no load it will show proper voltage, but looses it under load. Hope this helped.... CaptVR
I wondered when the question of checking voltage using a voltmeter would come up. The compressors Boot up sequence is much the same as the one in your computer. In the Danfoss BD compressor the Boot up on compressor start instantly in milliseconds tests six safety circuits, Voltage, fan amperage, current draw, motor armature acceleration, electronic module temperature and purity of electrical current. These safety circuits are the reason BD compressor's do not fail like other hermetically sealed compressors.

You would not find a Boot up problems on your computer with a voltmeter so do not waste time and money using it on BD compressors.
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Old 21-07-2019, 20:03   #15
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Re: Fridge cycling frequently for very short periods

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Originally Posted by Richard Kollmann View Post
I wondered when the question of checking voltage using a voltmeter would come up. The compressors Boot up sequence is much the same as the one in your computer. In the Danfoss BD compressor the Boot up on compressor start instantly in milliseconds tests six safety circuits, Voltage, fan amperage, current draw, motor armature acceleration, electronic module temperature and purity of electrical current. These safety circuits are the reason BD compressor's do not fail like other hermetically sealed compressors.

You would not find a Boot up problems on your computer with a voltmeter so do not waste time and money using it on BD compressors.
Perhaps you should look up Danfoss site. They specifically say that low voltage is a major problem, did not give a reason for low voltage. And sport, the only way to check it is with a quality VOM. They also will give you resistant loads for the three wires going to the compressor. Again you need a VOM, Do a little checking before you make quotes to what is correct diagnostics. You have two items, check your voltage, both static and running, if you got 12v then your controller is probably bad. There compressors are damn close to bullet proof, not so with the compressors controllers.
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