Freezer fridge defrosts when operated in a cold room

[Freesurfer]

I have a fridge/freezer unit in an off-grid solar powered cabin. The problem is that when the outside temperature drops and stays below below 8-9C or so during the colder season, the freezer compartment can't maintain its freezing temperatures, so the food inside defrosts and needs to be disposed off. There is no heating in the cabin during this period.

It is not a fault, the explanation is simple: The fridge only has one compressor cooling both compartments, and the thermostat only checks the temperature in the fridge compartment. When it gets cold, the compressor doesn't have to start as often (or at all) to maintain 4C in the fridge compartment. Which is fine for the fridge, but the same can't be said for the freezer. The the thermostat knob is cranked all the way to the coolest setting.

This is a common problem with all ordinary household fridges that are operated in places like a cold garage. In fact if you check the manual, it does state the temperature range it is designed for, so I can't really blame it.

However I didn't consider this issue when installing the fridge. So now I wonder, can someone think of a simple solution to the issue? One thing I have thought of is to modify it in such a way that the bulb inside always stays on and thus generates some heat that needs to be expelled from the fridge, thus forcing the compressor to run more often. But I have no idea what sort of wattage a common fridge can cope with. Installing too much will overwhelm the compressor and drain the battery bank. Install too little and it may not be enough to maintain sufficient cooling.

[Twoflower]

Have you checked, if the 4°C is actually maintained by the compressor? I could imagine that the cooling performance degraded or complete lost as the liquid/gas mixture in the cooling loop is too much condensed for the compressor to actually make the liquid evaporate in the inside of the fridge/freezer.

[Nusa]

For your existing fridge, look for "garage refrigerator kit", which basically is a heater for the refrigerator side for a cold weather environment. For off-grid, the increased energy requirements will be a factor, like you said. But any other approach might solve the freezer side at the expense of freezing the refrigerator side.

If these temperatures are only a night-time issue, and it warms up during the day, you may be able to add enough thermal mass in the freezer (e.g. frozen water in milk jugs) so the freezer will stay sufficiently cold without running over the night.

As for a permanent solution, I'd suggest buying a small chest freezer. Dodges the entire problem by not having a refrigerator side. Likely to be the cheapest solution as well, long term. You may be able to unplug the regular refrigerator entirely during cold weather.

[Gyro]

Yes, single compressor fridge freezers are fundamentally flawed when it comes to running at an ambient below the fridge thermostat setting. Separate fridge and freezer are of course the ultimate solution (checking the specs to ensure that they are suitable for "outbuilding" use.

One thing you could maybe try is buying a spare part freezer thermostat, fitting it in the freezer compartment and wiring it in place of (even in parallel with?) the fridge thermostat. I suspect that the fridge compartment will turn into an auxiliary freezer compartment, but it would probably solve your thawing problem. 

[NiHaoMike]

Simple solution is to add a thermostat to turn on the fridge light when the freezer is not cold enough and the compressor is not running. If it's incandescent, also fit a series diode to run it at half power. A SCR can be a clever way to do the part where it only turns on the light when the compressor is not running, by having the cathode connect to hot via the new thermostat, the gate to the existing thermostat via a diode and resistor, and the anode to the light.

I wonder if it might be possible to DIY an "ice motor" (kind of like a wax motor) to close off the vents to the fridge section and have the thermostat only operate based on the freezer temperature.

[tom66]

As for a permanent solution, I'd suggest buying a small chest freezer. Dodges the entire problem by not having a refrigerator side. Likely to be the cheapest solution as well, long term. You may be able to unplug the regular refrigerator entirely during cold weather.

Ditto this.  Our chest freezer is 'rated' for operation to -10C.  I suspect that it will operate just fine below that!   In the winter months where the garage was frequently around 0C, the power consumption for one month of operation was only 15kWh.  Or about 20 watts average consumption (probably 16% duty cycle.)   

[ejeffrey]

Chest freezers are also amazingly efficient due to thick walls and the top opening door, so they are a good choice for off grid applications.  Even if your batteries run out they have enough thermal mass and insulation to stay cold for a long time until the solar kicks in.

[Peabody]

One solution might be to set up an incandescent appliance bulb inside the bottom compartment, and have that powered by a relay or SSR outside, which in turn would be controlled by an Arduino with a temperature sensor attached.  The sensor would sense the air temperature in the garage, and turn on the relay with a duty cycle that depends on the garage temperature.  When it's very cold, the bulb might be on almost all the time.  At higher temps it would be on some of the time, and above, say, 50 degrees F, not on at all. Of course you would have to experiment to find the right algorithm, but something like this would give you roughly the right amount of heat needed to keep the frozen food frozen, but not have the compressor running all the time when it's warm outside.  I don't think the "garage kits" work that way.  An alternative would be to directly sense the temp in the freezer, but that might not work so well for defrost cycles or when you open the freezer door a lot.  If you measure the garage temp, then nothing actually connects to the fridge except the bulb holder and the leads going to it.  The relay, sensor and Arduino are all outside in a little box.

[MLXXXp]

Yes, single compressor fridge freezers are fundamentally flawed when it comes to running at an ambient below the fridge thermostat setting.

True for most, but not all.

I have an over 30 year old Inglis "System 2000" fridge/freezer with a single compressor. It has a microprocessor based electronic control system. There are separate temperature sensors for the fridge compartment and freezer compartment (and also one on the evaporator coil for defrost feedback).

It has a single fan in the evaporator assembly that, when on, blows into the freezer. There's a solenoid controlled air valve that controls whether or not air from the freezer can move through a channel from the freezer to the fridge (from the fan pressurizing the freezer).

The way it keeps both sections at the required temperatures is:

- If the freezer is okay but the fridge is too warm: Open the air valve and turn on the just the fan (not the compressor) to cool the fridge from the cold in the freezer.

- If the freezer is too warm and the fridge is also too warm: Open the air valve and run the compressor and turn on the fan to cool both sections (like a common fridge/freezer).

- If the fridge is okay but the freezer is too warm. (The OP's situation): Close the air valve and run the compressor and fan to only cool the freezer.

(There's also a case where the compressor is running but the fan is off, for a short time after defrost, to cool the hot evaporator down before blowing into the freezer.)

The controller also reads the fridge door operated light switch, which allows it to turn off the fan when the fridge door is open, so it's not forcing cold air out. According to the manual, it also uses the count and duration of door opens to help decide when to run a defrost cycle.

Unfortunately, I'm not sure how this helps the OP. Maybe, in a way similar to my fridge, a thermostat circuit could be added that senses the freezer temperature and tricks the fridge sensor into thinking it's too warm when the freezer is.

[amyk]

Relocate the thermostat sensing bulb to the freezer compartment and recalibrate it to the new temperature range, or change it to a control suitable for freezer use. Alternatively, if the length of tubing permits, and it's not already there, relocate it to the warmest part of the refrigerator.

[james_s]

I've had this same problem with the fridge at our cabin, if there's a cold snap and I've left ice cream in the freezer it melts. I've temporarily solved the problem by placing an incandescent nightlight inside the fridge on an extension cord over the coldest season but this is not totally ideal. I've been meaning to build a circuit to turn on the fridge light if the freezer gets too warm.

[Peabody]

One of these:

https://www.adafruit.com/product/1782

along with an Arduino, a relay, and a wall wart.  The relay could be one of these:

https://www.digikey.com/en/products/detail/omron-automation-and-safety/G3MC-202P-DC5/1789941

[Siwastaja]

Just get a proper dual compressor fridge/freezer, or even better, separate fridge and freezer. Installing heater to a fridge to let the flawed design "work" in an environment where it's not designed to work sounds like a horrible waste of energy.

Used freezers go in second hand internet services whatever you have there for a few dozen bucks.

[james_s]

The heater in this case need only produce a trivial amount of heat, it's more efficient than heating the room and it prevents the fridge from getting too cold and freezing things even if it's below freezing in the room. I don't know about the OP's case but in mine, the cabin is like a time capsule with all the original vintage appliances installed in 1973 so replacing the fridge is not something I'd want to do. It's true that a modern fridge would consume less power but the fridge is the only thing we leave on when nobody is there and the power it uses is not enough to exceed the base charge for having the electrical service connected.

[Peabody]

I've had this same problem with the fridge at our cabin, if there's a cold snap and I've left ice cream in the freezer it melts. I've temporarily solved the problem by placing an incandescent nightlight inside the fridge on an extension cord over the coldest season but this is not totally ideal. I've been meaning to build a circuit to turn on the fridge light if the freezer gets too warm.

Have you given any thought about how the circuit should work?  As I understand it, the "garage kit" offered by manufacturers supplies heat all the time.  That's no good.

It might be as simple as having the nightlight controlled by the added freezer thermostat.  But I'm not sure if there would be hysteresis issues.  And should the amount of heat generated vary with the ambient temperature?  What about defrost cycles?

It would be nice if we had the definitive, most efficient, circuit for the EEVblog garage kit, requiring no modifications to the fridge.  And of course, costing no more than $25.

[james_s]

Well my plan was to just switch on the light based on room temperature, right now I've just manually plugged it in and left it on all the time over the coldest part of winter which is less than ideal, but beats melted ice cream.

[Peabody]

As I described in reply #7, I was thinking of sensing room temperature too, but switching the heating element on and off, with the duty cycle determined by the room temperature, so as to provide only the heat that's needed.

I think there may also be an issue with extreme cold, where you don't want the compressor to turn on at all, but need heat in the lower compartment to keep the beer from freezing.  So you might need to run the main refrigerator power plug through a second relay to turn it completely off if it gets cold enough.  I don't think an attached garage would get that cold, but we should consider what to do when we get an arctic blast like last year.

[thm_w]

The way it keeps both sections at the required temperatures is:
- If the freezer is okay but the fridge is too warm: Open the air valve and turn on the just the fan (not the compressor) to cool the fridge from the cold in the freezer.
- If the freezer is too warm and the fridge is also too warm: Open the air valve and run the compressor and turn on the fan to cool both sections (like a common fridge/freezer).
- If the fridge is okay but the freezer is too warm. (The OP's situation): Close the air valve and run the compressor and fan to only cool the freezer.

But this is how most modern fridges operate, right. How else would you achieve dual temperature control?

They still say to not use them at low temperatures, eg LG: "Install this appliance in an area where the temperature is between 55 °F (13 °C) and 110 °F (43 °C)."

[MLXXXp]

But this is how most modern fridges operate, right. How else would you achieve dual temperature control?

My fridge is a freezer on top type. Maybe modern bottom freezer fridges have fancy electronic control. However, it looks to me that standard, average priced, top freezer models have either mechanical or electronic control for the fridge but if they have a separate control for the freezer, it's just a knob that mechanically varies size of the channel for air flow from the freezer section to the fridge section.

[thm_w]

My fridge is a freezer on top type. Maybe modern bottom freezer fridges have fancy electronic control. However, it looks to me that standard, average priced, top freezer models have either mechanical or electronic control for the fridge but if they have a separate control for the freezer, it's just a knob that mechanically varies size of the channel for air flow from the freezer section to the fridge section.

Yes I see what you mean now, I've only ever used bottom freezer type and it looks like they are at least a few hundred dollars more expensive. Part of what would pay for the electronic controls.

[james_s]

My fridge is a freezer on top type. Maybe modern bottom freezer fridges have fancy electronic control. However, it looks to me that standard, average priced, top freezer models have either mechanical or electronic control for the fridge but if they have a separate control for the freezer, it's just a knob that mechanically varies size of the channel for air flow from the freezer section to the fridge section.

That's the way the vast majority of domestic refrigerators have worked for decades. In the fridge there is either one or two controls, one is an electromechanical thermostat that controls the compressor based on the temperature in the fridge. The other knob, if present, moves a shutter mechanism to adjust the amount of air that flows down from the freezer into the fridge to adjust the balance between them. Some even fancier fridges have a slider on one or more of the produce drawers that work similarly, controlling a shutter that allows cold air from a duct to feed directly into the drawer.

[Peabody]

For future reference.  I have a Whirlpool freezer-on-top refrigerator vintage 1979 (barely broken in), and the thermostat crapped out on me recently.  Nobody local stocks the replacement, so it had to be ordered, and I needed to keep things cold over a weekend.  So I disconnected the two wires from the thermostat, and connected them together.  That turned on the fridge, but it would be always on.  So I plugged the main power plug into one of those 24-hour timers that let you turn things on and off at various times in 15 minute increments.  It wasn't as good as a working thermostat, but worked well enough to save my food for three days.

Anyway, it seems there are a number of ways of rigging things up to work in a garage that would be a lot better than installing an always-on garage kit.  I still prefer an Arduino-controlled PWM appliance bulb in the lower compartment, with duty cycle determined by the ambient temperature.  I'm planning on downsizing into a condo soon, and if the new place already has a refrigerator I may convert this old Whirlpool into a garage refrigerator, and see if I can get a circuit working.

[james_s]

I suggested my friend do the same thing last year when the thermostat in his chest freezer failed. It ran like that on a timer for about a month before he replaced the freezer. It was pretty beat up and tired looking so he had been planning on replacing it anyway.

Last year the PTC starter on my mom's refrigerator compressor failed so I rigged up a pushbutton for the start winding and plugged it into a power strip. I showed her how to turn on the power strip then immediately press the button to start the compressor and then shut off the power strip once it stops. That worked for several days to keep the food from spoiling until a replacement part arrived.