Temperature settings?

At what temperature should my freezer be set? What about the refrigerator?

Seems like I remember hearing the standard settings are 0[sup]o[/sup]F and 40[sup]o[/sup]F, respectively. Anyway, I’m pretty sure about the 40, not quite as sure about the 0.

Depends on where your fridge and freezer are! In my wife’s biochem lab they refer to them as the 4C, the -10C, and the -80C.
(This is in Canada, but even the students from the US instantly know what is being talked about.)

So 4 degrees Celsius is your fridge, -10 Celsius is a commercial freezer. Unless you want stuff to stay fresh for months and months (like, say toxic bacteria), you don’t really need a -80 C freezer.

Let’s start with the obvious: the temperature in the refrigerator is not uniform. So, for the refrigerator section I will have 0C or even a bit less at the coldest point. While water drops might freeze, other liquids or larger water containers will not. This is only a corner of the fridge and the rest is gradually warmer by a few degrees.

Some people have said -10C for the freezer and that would be sufficient for an old crappy refrigerator but -20C is more like it if you want to keep food frozen for any length of time.

It has always been my understanding that, for a regular 'ol refrigerator, the evaporator coil is only in the freezer, and the “coldness” simply “leaks” out into the refrigerator section (which makes sense). Yet our refrigerator has a temperature control for both the freezer and the refrigerator section. I’m curious: With only one evaporator (with refrigerant that only boils at the freezer temperature), how do you independently control the freezer and refrigerator temperatures? Does the controller for the refrigerator simply control a flapper valve that will allow more/less cold air to be transferred from the freezer compartment into the refrigerator section?

the answer is you can’t but this is no big deal. As you say, the temperature control is in the refrigerator section and the compressor runs enough to keep the right temperature there. Note that if the room is very cold, the compressor will run very little and will not keep the freezer section cold enough. You should not put such a refrigerator in a room that is colder than about 18C. Note also that as room temperature increase, the compressor runs more and the temperature in the freezer decreases.

Say the refrigerant is boiling at -25C in the evaporator coil… well you cannot get the freezer any colder no matter how much you run the compressor. So once the compressor is running enough (say 15 - 20%), running it more is not going to make a huge difference.

If the refrigerator is in a very cold room and the freezer is not keeping the temperature down, you can put some source of heat in the lower section (a small lightbulb will do) and this will make the compressor run more.

I hope this clarifies it.

oh, to clarify further, I was talking about your old, basic refrigerator.

Note that frost free refrigerators do not have the evaporator coil inside the compartment but they circulate air so the air can be separately directed to freezer and refrigerator depending on needs.

Also, some high end refrigreators may have two separate compressors.

A better refrigerator should keep at least -20C or -25C in the freezer.

CrafterMan - Yes. It is common practice for res. refrigerators to have one evap coil for the freezer, and simply divert a portion of the cold air to the refrigerator area. The freezer control changes the thermostat setting in the freezer, cycling the compressor and fan on and off when different temps are reached. The refrigerator control usually adjusts a damper type devide to divert more or less cold air. The thing to understand is that if you change the freezer temp, it will change the 'fridge temp. IF you change the 'fridge temp, it won’t affect the freezer temp at all, although it could change the time in the dead band area.

Common practice in the US for temps is 2 to 7 C (35-45F) in the 'fridge section, and -18 to -23 C (0 to -10 F) in the freezer section. Stand alone freezers are usually about - 29 C (-20 F). Those are at least common design point. People operate them however they like.

That’s what I figured - the set point adjustment for the refrigerator section refrigerator is simply a damper device to divert more/less of the cold air to the refrigerator section. (In other words, the refrigerator section doesn’t really have a true set point adjustment & closed-loop controller; it’s dependent n the freezer.) Thanks for the response.