Author Topic: How do I lower the temperature in my freezer....  (Read 5522 times)

denogail

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How do I lower the temperature in my freezer....
« on: November 04, 2013, 07:01:46 am »
OK...here is what I have.  I built my own box with 5 inches of good R value foam all around.  The freezer (dedicated) is about 3.5 cubic feet.  I have 2 Adler Barbours stacked one on top of the other (large evaporators), each with it's own thermostat control and compressor.  I remove the bottom plate of the top vertical evaporator so I could load frozen stuff straight through to the bottom evaporator.  I have had this system working now for 7 years, and stuff does stay frozen, but the temperature runs at about 22 degrees F.  Nothing goes bad at this temperature, and we are out in the Bahamas for 6 months.

The question is: How can I make the temperature lower.  Would changing the resistor value in the thermostat, thus making the compressor run faster lower the temp?  But, I seem to have read somewhere, that the Danfross compressor should not run more then a 50% duty cycle...true or false?  Right now, I believe my duty cycle is around 25%, so I think I could afford to run the compressor at a  higher speed.  What do you think, and what resistance value should I use in the thermostat?

BTW...the top evaporator runs much more then the bottom, due to the coldness sinking, holding the bottom evaporator off.  But the bottom does turn on once in a while.  When this does happen, the temperature in the box drops to around 0 degrees F and slowly warms up to 20 or so degrees.

Again, all works well, and the fish and lobster stay frozen, but I would like to get it alittle colder.  Thank you for your reading time.

Dennis

Richard

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Re: How do I lower the temperature in my freezer....
« Reply #1 on: November 05, 2013, 04:53:58 pm »
Two systems one box location of evaporators confusing without pictures.

Want to get this freezer colder, compressor runs only 25% of the time. Will increasing compressor speed get box colder.?------Answer: probably not by increasing compressor. Only by compressor running time by lowering thermostat will make box get colder.

Compressor running time controls box temperatures. Reducing compressor speed improves daily amp-hrs of energy consumed. Increasing speed will shorting running time only and it is already not running enough.

If thermostat when set full cold will not get compressor to run long enough you may not have a freezer thermostat.

denogail

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Re: How do I lower the temperature in my freezer....
« Reply #2 on: November 06, 2013, 06:58:49 am »
Thank you Richard for your reply.  As far as to evaporators in one box..let me try to explain again.  These are the large evaporators by Adler Barbour (now Dometic).  The first vertical evaporator mounted on the back wall down at the bottom of the box.  The second evaporator, I removed the thin metal bottome plate of the second vertical evaporator by drilling out the pop rivits and then mounted this evaporator on the back wall on top of the first.

Now you mentioned a freezer thermostat...is there such a think?  Where can I get 2...?

Is it possible to put an extra piece of insulator between the sensing bulb and the evaporator on the side?  Would this trick the existing thermostat to think that the evaporator is not getting cold enough to turn off, and run longer?

Thank you  DenO
« Last Edit: November 06, 2013, 07:01:55 am by denogail »

Richard

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Re: How do I lower the temperature in my freezer....
« Reply #3 on: November 06, 2013, 10:38:30 am »
Your present Adler Barbour thermostats are most likely Danfoss standard refrigerator Evaporator thermostats. They sell anywhere from $15 to $60 depending on where you buy them. Best to buy the Service pack it comes without the outer plastic cover and is cheaper.
Danfoss Refrigerator thermostats cycle between +7 and +36 degrees F depending on knob setting while Freezer thermostats cycle between -2 and +18 degrees F.

To be more efficient these Icebox units cycle on evaporator temperatures and not box temperatures. Controlling evaporator temperatures results in a warmer box temperature so temperatures are not defined on control knob just numbers from one to ten.

Because you have two separate units working in the same box I would run only one compressor to set that thermostat. Then with first compressor off run second and set it to desired box temperature This may be the only way to balance both systems to together as dial settings will always be different do to position of evaporators.

To recalibrate thermostats it is possible to lower box temperatures by reducing thermostats temperature sensing tube contact with evaporator. Adler Barbour recommends correct refrigerator calibration with 5 inches of tube clamped to evaporator try reducing that to 2 inches to achieve freezer temps.


denogail

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Re: How do I lower the temperature in my freezer....
« Reply #4 on: November 06, 2013, 05:48:24 pm »
Once again, Richard, thank you for your input....always ask the pros which you are!

I will reduce the sensing tube contact down to 2 inches or so.  One final question, please...is it true that the compressor cannot or should not run more then a 50% duty due to the possibility of premature failure?

Thanks again...very much...DenO

Richard

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Re: How do I lower the temperature in my freezer....
« Reply #5 on: November 07, 2013, 07:12:04 am »
When the BD 50 compressor is installed in an air cooler condensing unit like the Adler Barbour it is not limited in daily running time hours. One warning from Danfoss is if compressor is running at 3500 rpm control module should have a small fan blowing air on its metal heat-sink.

I have referred to 50% compressor duty cycle in two applications: When selecting the correct size compressor I want 50% more capacity growth if planed use climate conditions change. The other times I use the 50% duty cycle or less in setting compressor speed for lowest daily power consumption.



denogail

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Re: How do I lower the temperature in my freezer....
« Reply #6 on: November 09, 2013, 06:50:51 am »
Good morning Richard...anyways...morning is here.  In looking at the wiring diagram for the standard tstat, I see that only two wires of the 4 are used for the standard tstat.  This means that the tstat itself is a simple switch, depending of course where the knob is set to turn on and off.  In tracing the yellow and green wire back to the compressor control module, it appears to me that the tstat switch when it gives the command to turn on the compressor,  is simply suppling a ground signal to the brown wire as it goes into the compressor control module plus a resistive value for speed.

Question...please....is it possible to control both compressors/evaporators with a single tstat.  The reason you ask....is I have noticed over the years that this system has been running is that: When the bottom evaporator does turn on (and doesn't happen to often...because the top evaporator works more dropping the "coldness" down to the bottom of the box, holding the bottom evaporator off) the temperature in box drops down to around 0 degrees F.

So, do you think it is possile to take either tstat, disconnect the wires from one and tie the yellow and greens wires together, respectively to control both evaporators/compressors with one tstat?

Thank you again...DenO

Richard

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Re: How do I lower the temperature in my freezer....
« Reply #7 on: November 09, 2013, 03:02:32 pm »
Present Danfoss thermostat circuit is a two wire switch operating a one to five milliamp microprocessor inside control module. If you tamper with this circuit you might damage one or both units control modules.

I gave you a solution of balancing one system’s thermostat at a time with the other turned off. This is how dual systems in one box are normally controlled.

If you want one system to start both compressors then you will need an added relay controlled by the primary compressor’s small plus + and F terminals and closing yellow and green thermostat circuit on other thermostats wiring.

denogail

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Re: How do I lower the temperature in my freezer....
« Reply #8 on: November 10, 2013, 07:09:57 am »
Thank you Richard for the info on the small + and the F wires running a small relay to provide a  closure to the yellow and green wires on the other tstat for an ON signal.

I will do this...however..just one last question and I think I know the answer to this...but when in doubt, one should ask the expert...Should I use the top evaporator/tstat as the master or the slave or the bottom evaporator/tstat.  As I mentioned in an earlier post, the top evaporator/tstat cycles much more then the bottom, and the coldness that that produces sinks down to hold the bottom off.

Thank you again for your time...

DenO

Richard

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Re: How do I lower the temperature in my freezer....
« Reply #9 on: November 10, 2013, 07:41:49 am »
If Complete Box is a Freezer then use top evaporator system as master control.