Talk:Refrigerators on Shabbos

See the discussion of old refrigerators on the main page.

Refrigerators Today

Today, manufacturers are introducing new electronic systems into the refrigerator.

Auto Defrost When warm air comes into contact with a cold surface it will condense and stick to the surface- much like a window pane in winter. In freezing temperatures the frost will accumulate and turn into a thick layer of ice. Inside the freezer walls, manufacturers install a heating coil –like the coils found in a toaster oven- that burns red-hot and melts any frost buildup. (The small amount of excess water is drained into a tray underneath the refrigerator where it evaporates).

There are three methods used to turn on the defrost coil:

'Method 1'- Defrost Timers In older refrigerators (1980), the defrost coil is activated with an internal timer.

'Method 2'- Adaptive Defrost Instead of activating the defrost on a timer, a computer calculates the compressor run time only, and then turns it on every few hours for a short period. This is a real problem to use on Shabbos. If the refrigerator door is opened, hot air that enters causes the temperature to rise and the compressor needs to run longer to keep the food cool. Longer compressor run time means the defrost cycle activates sooner than it would have. According to many poskim this is a serious concern. Causing the heating coil to ignite is d’oraysa- a biblical prohibition. The defrost coil is a gacheles shel mateches, which is classified as igniting a flame - havarah.

Method 3- Electromagnetic Sensors These are usually embedded inside the door and undetectable. They count how many times the door is opened and closed. The door sensors count the number of times a refrigerator door is opened and closed and activate the coil after a certain number of times. The reason they use this method is that the more the door is opened the more warm air is let in causing ice buildup. So for an example, after 20 times of warm air entering the refrigerator, they estimate, the freezer needs a defrost cycle. Here, opening the door constitutes a direct action of igniting the defrost after a certain amount of times the door is opened even if unintentional.

Damper and Fan In sectioned refrigerator/freezer models, cold air generated by the compressor is channeled only into the freezer. Located beneath the freezer panels, is an electronic air vent called the damper. When the thermostat feels the temperature in the refrigerator is too warm the damper opens, allowing cold air to flow from the freezer into the refrigerator. The air is then dispersed around the refrigerator section by a fan. The fan is directly affected by opening the door and the damper is affected by the thermostat. At one point buttons could be easily taped down. Today, in many refrigerators these electronics are triggered by electromagnetic sensors located in the door panel. Taping the buttons will no longer prevent the sensors from activating the damper and fan on Shabbos.

Electronics, Microprocessors and Messaging

An electric circuit simply powers machines with electricity. However, an electronic circuit can interpret a signal or an instruction, and perform a task to suit the circumstance.

Modern refrigerators use a combination of electronic and electrical circuitry. A refrigerator has auto defrost, compressor, damper vent and fan, and digital thermostat. The electronics decide when to activate each of these. For example, when the temperature is set via the control panel or dial inside the refrigerators, the instructions are interpreted by microprocessors. When the electronic circuit has interpreted these commands, it sends signals to the electrical circuit to operate the compressor, defrost or other systems, to keep systems at optimum performance levels and the food temperatures stable.

So each time the door is opened the microprocessor makes many changes to the calculations so that it can adjust the systems accordingly: How often to turn on the compressor, when to open the damper vent, how wide to open it, when to turn on the defrost, etc. Every change in calculation creates a new electronic switch in the circuitry.

In Eretz Yisrael, most poskim today forbid using a refrigerator on Shabbat without some type of Shabbos mode switch. More recently refrigerators are being made with approval from Kashrut organizations that ensure these systems are not tampered with on Shabbos.