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Old 21-07-2014, 01:34   #1
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How to test a fridge?

I have the wireless temp monitor - very great device!


The temperature in the cold compartment does not go below 12 deg Celsius, freezer is 0.. -1. There is ice outside the freezer, but only half of surface.
Which is not enough - food goes bad.

The compressor looks working normally around 50% of the time, starts and stops.

I am thinking about bad thermostat, how to test it? Thinking to put a digital thermostat with two wired temp sensors.

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Old 22-07-2014, 13:47   #2
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Re: How to test a fridge?

You are correct a 50% compressor duty cycle and box does not reach desired box temperatures would indicate less than desirable performance. What happens if thermostat is set at full cold for a full day? If compressor still cycles off at 50% or in less time and desired box temperature is not reached, thermostat is your problem. If full cold setting of thermostat extends compressor running time and compressor keeps running all the time and does not cycle there is a problem with refrigeration unit performance.

Is this an Isotherm unit with a through hull condenser? If so, Does it have a Isotherm ASU module mounted on Danfoss electronic control module?

Is there air space around evaporator chamber or is it tight against top and box side walls?

Is the small aluminum long thermostat temperature sense tube touching cold evaporator anywhere other than where it is supposed to at the end? It would be a mistake to install an electronic thermostat as was suggested.
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Old 29-07-2014, 04:45   #3
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Re: How to test a fridge?

Pardon, the tech details:

Danfoss BD50F compressor
101N0210 electronic controller (connected to temp sensor on the compressor and analog temp regulator in the box).

I have shorted the thermostat connection - the compressor is running 100%. Let's see - if the temp will drop - then I change the thermostat. If not - refilling the compressor with 134a freon, then taking it for repair...
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Old 29-07-2014, 06:31   #4
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Re: How to test a fridge?

Quote:
Originally Posted by SVI View Post
Pardon, the tech details:

Danfoss BD50F compressor
101N0210 electronic controller (connected to temp sensor on the compressor and analog temp regulator in the box).

I have shorted the thermostat connection - the compressor is running 100%. Let's see - if the temp will drop - then I change the thermostat. If not - refilling the compressor with 134a freon, then taking it for repair...
If you want to eliminate thermostat circuit completely on an Isotherm unit place bypass connection between C and T terminals on 101N0210 module. This will cause compressor to continue to run but at 2,000 Rpm.

Warning. if you or anyone tampers with refrigerant before confirming with several tests that refrigerant is the problem you will feel the pain. Messing with refrigerant on a very small system is like shooting yourself in the foot, costly and pain lasts for a long time with several doctor calls.
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Old 29-07-2014, 06:34   #5
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Re: How to test a fridge?

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Old 29-07-2014, 07:11   #6
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Re: How to test a fridge?

Quote:
Originally Posted by Richard Kollmann View Post
If you want to eliminate thermostat circuit completely on an Isotherm unit place bypass connection between C and T terminals on 101N0210 module. This will cause compressor to continue to run but at 2,000 Rpm.
This is what I just did. No change in temp. My compressor has a resistor to run at 3500rpm.

Quote:
Warning. if you or anyone tampers with refrigerant before confirming with several tests that refrigerant is the problem you will feel the pain. Messing with refrigerant on a very small system is like shooting yourself in the foot, costly and pain lasts for a long time with several doctor calls.
The online manual at one of the web forums says add the refrigerant up to the point the compressor consume 5 amp and the return line does not freeze. If too much refrigerant - do 5 sec bursts by releasing the valve.
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Old 29-07-2014, 09:24   #7
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Re: How to test a fridge?

Quote:
Originally Posted by SVI View Post
This is what I just did. No change in temp. My compressor has a resistor to run at 3500rpm.



The online manual at one of the web forums says add the refrigerant up to the point the compressor consume 5 amp and the return line does not freeze. If too much refrigerant - do 5 sec bursts by releasing the valve.

You started this thread by saying compressor cycles at a 50% duty time. At 3500 Rpm and too much refrigerant amperage would need to reach way more than 9 amps before module detected an overload.

When you bypassed C and T terminals there was no speed resistor and if you let compressor keep running yes it will run much longer without a resistor but it will eliminate thermostat as the cause of compressor cycling before desired box temperature is reached..

If this is what manual said it is DEAD WRONG ["The online manual at one of the web forums says add the refrigerant up to the point the compressor consume 5 amp and the return line does not freeze. If too much refrigerant - do 5 sec bursts by releasing the valve."] If no one has tampered with refrigerant you suddenly do not have too much. If there is not enough or no refrigerant at all compressor will run anyway.

I ask you a question about condenser cooling before, have you cleaned the condenser air, water or through hull recently? This is important as poor condenser cooling increases refrigerant volume, high pressure, and system current draw. What code signal are you receiving from trouble shooting LED.
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Old 29-07-2014, 09:58   #8
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Re: How to test a fridge?

Judging from the photo of the box opening, it appears that your box is inadequately insulated.
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Old 29-07-2014, 11:27   #9
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Re: How to test a fridge?

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Judging from the photo of the box opening, it appears that your box is inadequately insulated.
It is a factory box from Fountaine Pajot. These guys know how to build boats.
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Old 29-07-2014, 11:30   #10
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Re: How to test a fridge?

Quote:
I ask you a question about condenser cooling before, have you cleaned the condenser air, water or through hull recently? This is important as poor condenser cooling increases refrigerant volume, high pressure, and system current draw. What code signal are you receiving from trouble shooting LED.
It is air-cooled. Ambient temp is 26-30 C (air-conditioned).
My thought is has no enough 134a, I am going to add some and see the results. If too much added - easy to release some.
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Old 29-07-2014, 11:55   #11
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Re: How to test a fridge?

Quote:
Originally Posted by Terra Nova View Post
Judging from the photo of the box opening, it appears that your box is inadequately insulated.
Looks to me like 4-5" of insulation in a free box whose sides are not against the hull or machinery room. How much do you consider adequate?

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Old 29-07-2014, 13:13   #12
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Re: How to test a fridge?

Quote:
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It is a factory box from Fountaine Pajot. These guys know how to build boats.
That could be. But do they know how to build a reefer/freezer? Sounds like not.

Hard to tell from 1 photo, but it looks like only 2-3" of insulation? And not much of a lid gasket at all. Any UV or vapor barrier?
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Old 29-07-2014, 14:53   #13
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Re: How to test a fridge?

UV barrier? How do you suppose UV is getting to it? Does anyone have a UV barrier in their box?

This is really only a reefer - the freezer component is just what is enclosed in the small evaporator box.

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Old 29-07-2014, 17:36   #14
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Re: How to test a fridge?

Meant IR, infrared.
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Old 29-07-2014, 21:14   #15
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Re: How to test a fridge?

OK, does anyone have a specifically unique IR barrier in their box? IR is heat - that is the purpose of the insulation itself. Any specific barrier, like a foil, would be part of the insulation properties.

So one only needs to be concerned with the overall insulation value - not with any specific IR barrier. For example, a 1" vacuum panel is a better IR barrier than 3" of foam. Thin foil itself adds little value.

The vapor barrier is a valid point. However, the OP's box is more amenable to being just fine without a vapor barrier than most due to its location and build.

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