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Old 12-03-2017, 04:35   #1
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Freezer won't stay cold

This freezer is driving me nuts. I recently bought a catamaran with a non working freezer, it only had an evaporator in it but all the seals were good. I had a refrigeration company install a Danfoss db50 compressor and Evco controller and new probe. The installer expressed concern that the plate was probably too small to get to minus 19(Celsius) but should get around zero. It got to minus 4 but after a short time would drift up to + 12 to 14. They installed a fan inside but that did nothing. Another tech regassed it and I've had the resisters changed 3 times. I've cancelled the defrost settings but nothing seems to stop the freezer drifting back to about 14 C. It's not low voltage as I'm on shore power so the batteries are all good. Surprisingly all I need to do is open the lid and the compressor will kick in and the temp goes back down. If I turn the power off and on it restarts and goes down as well. Can anyone suggests why this freezer won't stay down around zero or less. I accept it may not get all the way to minus 19 but I'd like it to stay around zero our less. Any thoughts would be greatly appreciated. Thanks
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Old 12-03-2017, 06:42   #2
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Re: Freezer won't stay cold

Hi Brad
First thing , what are your ambient temperatures ? And how well is the space you have the condensing unit (compressor) ventilated ? The first thing you may want to do is get more airflow across the condenser . Also make sure it is clean and unobstructed .
Next thing you want to check is where you have the sensor , opening the lid indicates and having the unit run indicates it may be in a poor position . Does your controller have two temperature sensing leads or one ? You may also want to try and bypass the controller completely by removing its connections from the controller on the C, T, terminals and placing a simple jumper wire across those connections . This will remove the thermostat from the equation and just allow the compressor to run steady . The controller is the small black box that is attached to the compressor.

See how that goes and let us know .

Regards John
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Old 12-03-2017, 06:53   #3
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Re: Freezer won't stay cold

Hi Brad,

You say "when you open the lid" the compressor starts up again.

This sounds like a thermostat problem, doesn't it?

My big fridge had the thermostat chopped out by the previous owner (sunsail) so I put in a 12 volt timer that dies many sequences per day.

You could do my test if its the thermostat by putting the purple wire off the compressor. (Mine is purple, dunno about yours).

Then either replace the thermostat or go onto a time based method.

Could a corroded thermostat connection be the cause? As in clean it up and see?
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Old 12-03-2017, 07:11   #4
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Re: Freezer won't stay cold

It sounds like the Evco controller is your problem. I would recommend disconnecting Evco thermostat to test the compressor and evaporator's performance. A thermostats purpose on a Danfoss BD 50 powered system is to open and close a very low one to five milliamp circuit inside the Danfoss electronic module. By disconnecting wires C and T on Danfoss module and placing Terminals C and T together with a jumper wire compressor will run all the time when power is turned on. It is also important to know if there is a wire connected to module P terminal? Best to not have wire on P terminal.

With nothing to stop compressor turn power ON to refrigerator and let system run for 4 hours or more to see how cold the box will get. Now turn power off and see how long it takes for box temperature to rise to about 5 degrees above desired normal box temperatures.

True efficiency of the BD50 compressor and other system components is when compressor runs less than 50% of the time when compressor speed is set as low as possible and still maintains desired box operating temperature.

If it is confirmed evaporator lacks in thermo heat conductivity in this test Fan forced air of 15 to 25 cfm blown across evaporator will improve its performance.
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Old 12-03-2017, 09:57   #5
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Re: Freezer won't stay cold

I cut out a portion of an old Closed Foam, camping "ensolite" pad. I just place it underneath the top opening. Helps lots with efficiency.
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Old 12-03-2017, 14:40   #6
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Re: Freezer won't stay cold

Thank you all for the responses. If I bypass the thermostat by jumping the C+T terminals how do I stop the compressor from running 24 hours a day while I'm not on the boat. I won't be on shore power all the time. I'll definitely give it a try just wondering what to do next if it is the thermostat. In answer to the other questions, I placed an extra fan to blow directly over the compressor but it didn't change anything, the ambient temperature in the boat is pretty good (I'm in Melbourne and its not that hot) and the insulation and lid seems pretty good. Thanks again for the advice I'll let you know how I go.
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Old 12-03-2017, 15:14   #7
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Re: Freezer won't stay cold

Excellent you are half way there . Seems you have good airflow around your condenser. Putting a jumper across the c and t is just for a test , just to confirm that the thermostat is the issue . Now once it proves that your thermostat is the problem then you would want to get a new one asap. Nobody wants to be a human thermostat . Maybe consider a mechanical one designed for a system that should be controlled with evaporator temperatures , not box temperatures . You can get them spicfically for a freezer . They will have the appropriate compressor delay built in (hysteresis).

Regards John
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Old 13-03-2017, 02:49   #8
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Re: Freezer won't stay cold

Have you checked there is actually any insulation surrounding your fridge/freezer/cold box?

Sounds daft but sadly most boat building companies will spend thousands on fancy lights, fully integrated entertainment systems then install a fridge without any insulation.

I discovered this was the case in my boat when I investigated why our fridge seemed to be running all the time. Basically the cold box was a simple plastic "bucket" with a cold plate at one end and a compressor underneath.

As retrofitting any insulation outside was going to involve a complete galley refit I thought inside the box for a change and lined the fridge with 10mm of closed cell foam (camping mat) all round and including under the lid. Then added a further 15mm of dense corrugated card covered in thick aluminium foil under the compartment to reduce the heat load entering from the compressor below. Since then I have also added an additional cooling fan to aid the air circulation below.

The result is my compressor now runs for 15mins to cool the interior down to -4ºC then sits twiddling its thumbs for 75mins. Massive reduction in the amp/hrs and fresh chicken for 3 days.

Worth having a look before you blame the compressor

Cheers and cold beers

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Old 13-03-2017, 03:41   #9
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Re: Freezer won't stay cold

Quote:
Originally Posted by MarkJ View Post
Hi Brad,

You say "when you open the lid" the compressor starts up again.

This sounds like a thermostat problem, doesn't it?
My thoughts exactly.
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Old 13-03-2017, 05:46   #10
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Re: Freezer won't stay cold

I learned a trick years ago when having cooling problems with RV refrigerators. Because of all the jostling and weird angles that they are subjected to, the coolant that circulates around the unit will develop air pockets restricting the flow. We would simply empty the fridge and pull the unit out and flip it over on its top. After letting it sit for a few hours, flip it back over and reinstall. This tended to do the trick. If not, it only cost a couple bags of ice and a few hours time to try it out.
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Old 13-03-2017, 06:48   #11
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Re: Freezer won't stay cold

Quote:
Originally Posted by bradandnatalie View Post
how do I stop the compressor from running 24 hours a day while I'm not on the boat. I won't be on shore power all the time.
I shall reiterate the excellent knowledge spewed forth but obviously unread, from my last post...


You can buy a 12 volt timer that turns on and off 16 times per day.
I use that to regulate my big fridge that basically only has drinks in it. Coming up to 5pm when Sundowners are called, all the beer is cold.
But when the batteries are low, 1am till 8am its only on 5 minutes per 2 hours...
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Old 13-03-2017, 07:09   #12
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Re: Freezer won't stay cold

Quote:
Originally Posted by bradandnatalie View Post
Thank you all for the responses. If I bypass the thermostat by jumping the C+T terminals how do I stop the compressor from running 24 hours a day while I'm not on the boat. I won't be on shore power all the time. I'll definitely give it a try just wondering what to do next if it is the thermostat. In answer to the other questions, I placed an extra fan to blow directly over the compressor but it didn't change anything, the ambient temperature in the boat is pretty good (I'm in Melbourne and its not that hot) and the insulation and lid seems pretty good. Thanks again for the advice I'll let you know how I go.
The ONE TIME TEST I defined was to answer your earlier questions about compressor control module or thermostat controlling cycling, Question about evaporator Btu capacity and Question about box insulation's rate of heat gain.

A good equilibrium temperature of -27 C (-16 F) can be reached between refrigeration system and box heat gain is generally expectable if compressor runs several hours without it cycling off by a thermostat.

At the end of the above performance test the compressor was to be turned off with power circuit breaker. Recording time when compressor stopped and again when box temperature increased to a few degrees above a point where desired box temperature is achieved this is a reasonable reference to insulation’s present R value.
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Old 13-03-2017, 10:39   #13
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Re: Freezer won't stay cold

Hi, I have done a lot of refrig. work and Mark has the right idea. It sounds like a thermostat problem. You can hot wire it to check the problem but you DON'T want to leave it that way, you will burn up your new comp. Get a new thermostat to replace it so it will cycle properly.
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Old 13-03-2017, 13:54   #14
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Re: Freezer won't stay cold

If the thermostat idea does nothing then it could be moisture in the system. If it was open for a while then a separate dryer should be Installed.
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Old 13-03-2017, 14:02   #15
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Re: Freezer won't stay cold

Quote:
Originally Posted by bradandnatalie View Post
Thank you all for the responses. If I bypass the thermostat by jumping the C+T terminals how do I stop the compressor from running 24 hours a day while I'm not on the boat. I won't be on shore power all the time. I'll definitely give it a try just wondering what to do next if it is the thermostat.
Replace the thermostat?
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