Thermostat: Selection, Types, Function

Thermostats: Selection, Function and Design

The thermostat is one of the components that most often causes trouble in the domestic refrigerator. Due to the large number of different thermostat types, it is often difficult to obtain replacements. Various manufacturers are increasingly producing OEM series, for which replacements are usually not available at all or only at lunar prices. We have a wide range of models from various manufacturers such as Danfoss, Ranco, Atea, Mikrone, Alco, Prodigy in our delivery program. If you can not find a suitable model in the core range with us, please simply contact our customer service, which will advise you on the selection of a suitable alternative.

In this blog post, I would like to give you a brief overview of which aspects play a role in the selection of a suitable comparison thermostat. So you can choose yourself a successor model or a suitable service thermostat for your thermostat.

The following attributes are relevant for thermostats:

• Temperature switching values (Contact opening and Contact closing for Cold and Heat)
• Capillary tube Sensor length
• Contacts (Number, Position, Size)
• Automatic Defrosting Function (Constant Restart Temperature)

If you are looking for a suitable replacement for your thermostat, it is important that you find a thermostat with comparable properties to the thermostat you are already using. The overview and filter functions in our store will support you in the best possible way. Even though it is important that you find a thermostat that has as much as possible the same properties as the one originally installed, not everything has to be exactly the same as the original. As a rule, this is not even possible. For example, the capillary tube may be longer (the part that is too long then simply remains coiled - it must not be cut off!) and the switching values are slightly different. Other contact sizes can often be solved with other cable lugs, etc. The important thing is that the rough functional values match, so that your cooling unit promptly cools properly again.

Designs

By and large, all thermostats are used for temperature control, but there are two main types in refrigeration: the standard adjustable thermostat, respectively. Differential Thermostat for wall mounting (sheet metal console mounting) and the refrigerator thermostat or Service Thermostat . The ordinary thermostat (also known as a thermostatically controlled changeover switch) consists of a thin pipe filled with liquid, gas or steam, a temperature sensor and two contacts with which the temperature in the refrigerator is controlled and monitored. The refrigerator lighting is connected to a contact via a door switch. The other contact switches the compressor on or off according to the set temperature and the temperature inside the refrigerator. If the room temperature falls below the set value (warm on), the heating contact closes. If the room temperature rises above the setpoint (cold on), the cooling contact closes. There are many thermostats that look similar on the outside, but the appearance of the thermostats does not matter. But you can very well distinguish a differential thermostat from a service thermostat from the outside.

A mechanical Differential Thermostat for room temperature control has two separately adjustable scales on the front: on the left for setpoint (upper switching value) and on the right for differential setting (Hysteresis). On the left scale the upper switching value (upper switching value) is set and on the right - the difference. The switch-off value (lower switching point) corresponds to: value on the left (upper switching point ) minus difference.

An example: Value on the left "-5" °C, value on the right "4" °C - results in a switch-off value of -9 °C.

In the case of Differential Thermostats, the change in volume during the Temperature change is transmitted to a diaphragm and further to a snap-action switch of the capillary tube. The operation is clear and, above all, very simple, as the Temperature can be set by simply turning the knob.

A Service Thermostat or refrigerator thermostat is an ordinary Thermostat with fixed hysteresis. These are often used in refrigerators and freezers and are commercially available in countless variants. Service Thermostats are relatively inexpensive and can be easily found through our product database.

Error analysis

It is often unclear whether the thermostat is the cause of malfunctions in the refrigerator.

In the following cases you can be almost certain that there is a problem with the thermostat:

- the Refrigerator no longer cools

- the Refrigerator cools without interruption-> strong ice formation (Compressor does not switch off and runs constantly).

Reading the Switching values

It is often asked how to read the Temperatures on the thermostat-> they are defined as follows:

- Pos. warm on / off: +2°C / -5.5°C. / at lowest & set level

- Pos. cold on / off: -13.5°C / -25°C. / at highest set level

When a Thermostat works at minus temperatures, as in this case, it is imperative that the sensor is in firm contact with the evaporator plate. If this is not possible, the thermostat is not working properly. It would never switch off in this case and the compressor runs continuously..

Electronic Thermostats or Refrigeration controllers are used for room temperature control with defrost limit and to display the actual room temperature, which is often an advantage. More info on Refrigeration controllers can be found in a separate blog post.

Universal Replacement Models

In our store you can find some universal Thermostats available from stock, which can replace the majority of Refrigerator Thermostats in case of repair due to extra wide Temperature range and longer capillary tube. Here is a brief listing of them:

Thermostat RANCO K50-H1107000, VB107, max.+2/-3; min.+12,5/ ; L = 2000 mm

Thermostat RANCO K50-H1104001, VC101, max.-/-22,5; min. +2/- 5; L = 1200mm

Danfoss Service Thermostat 077B7003, Capillary tube 1.6 m for Refrigerators with automatic defrosting

Service Thermostat Danfoss 077B7001, Capillary Tube 1,3 m

Service Thermostat Danfoss 077B7002, Capillary Tube 1,3 m, Push button defrost

Only for Hobbyists:

https://frigopartners.com/room-thermostat-pbarigy-f2000-35-35-0c-l-1-5-m

This Differential Thermostat can be mounted externally and the sensor can be fixed in the room. When the housing is removed, the Thermostat is like all Ranco K.... Types and can be mounted inside the Refrigerator.