A refrigerated display case is a critical element in the trade of perishable goods, since the safety of products depends on the correctness of its operation and customer safety. Errors in setting the thermostat can lead to damage to expensive goods or, conversely, to excessive energy consumption and over-drying of food. Understanding the principles of operation of cooling equipment allows the operator or store owner to maintain an ideal microclimate inside the chamber.
Many users are faced with the fact that the values displayed on the display do not coincide with the actual temperature inside the chamber, which causes confusion and requires intervention. This is due to the inertia of the system, the location of the sensors and the characteristics of air flow circulation. In this article we will look at how to properly calibrate equipment, take into account external factors and set up modes for various groups of products.
Modern models, such as Polar or Carboma, are equipped with complex electronic control units that require careful attention. However, even simple mechanical thermostats require periodic checking and adjustment. Proper tuning is the key to a long service life of the compressor and stable quality of the products sold.
Principles of operation and types of thermoregulation
It is fundamentally important to distinguish between the two main types of temperature control, since the algorithm of actions for them is radically different. Budget models often use a mechanical thermostat that responds to changes in refrigerant pressure or the expansion of a special liquid in a capillary tube. Electronic controllers, in turn, read data from temperature sensors (thermoresistors) and control the compressor with high accuracy up to a degree.
The electronic system allows you to set not only the on and off temperature, but also regulate the speed of fans, defrost timers and an open door alarm. Digital controller is the brain of the display case, which processes hundreds of readings per second. The mechanics work on the principle of simply opening the contacts when a certain point is reached, which often leads to wider temperature fluctuations inside the chamber.
⚠️ Attention: When working with mechanical thermostats, avoid sharp rotation of the handle. The rotation should be smooth, with an interval of 10-15 minutes between changes, so that the system has time to react and stabilize the pressure in the circuit.
The location of the temperature sensor also plays a key role. In cabinets with dynamic cooling (with a fan), the sensor is usually located in the air suction area to monitor the temperature of the returning flow. In static models it can be built into the wall or located next to the evaporator. Understanding where exactly your display case “feels” will help you avoid mistakes when setting up.
Optimal temperature conditions for various products
There is no single “ideal” temperature for all products, since biochemical processes in meat, dairy and vegetables proceed at different speeds. For example, fresh meat requires lower temperatures to suppress the growth of bacteria, while fruits, when strongly refrigerated, lose their taste and texture. Freezing certain types of products in a regular display case are unacceptable if it is not intended for this.
Dairy products are characterized by a narrow range, going beyond which leads to rapid souring or, conversely, crystallization of the structure. Vegetables and fruits require not only a certain heat, but also high humidity, so their storage in display cases with intense airflow should be limited in time or protected with special films.
The following is a table of recommended modes that should be followed to ensure maximum safety:
| Product type | Recommended temperature (°C) | Permissible deviation | Shelf life (max) |
|---|---|---|---|
| Fresh meat (chilled) | from -1 to +2 | ±1°C | 3-5 days |
| Dairy products | from +2 to +6 | ±1.5°C | 5-7 days |
| Vegetables and fruits | from +4 to +8 | ±2°C | 7-10 days |
| Confectionery | from +2 to +8 | ±2°C | 3-5 days |
| Chilled fish | from -2 to +1 | ±0.5°C | 2-3 day |
The coldest zone is usually located at the back wall and at the bottom of the chamber, closer to the evaporator air ducts. Place the most sensitive goods exactly where it is colder, and less sensitive ones in the foreground.
Step-by-step instructions: setting up the electronic controller
Setting up an electronic storefront begins with unlocking the control panel, since most models have protection against accidental changes to parameters. This usually requires pressing and holding a specific key combination for 3-5 seconds. Often this is a button with a picture of a lock or simultaneously pressing the up and down arrows.
☑️ Basic controller setup
After entering the menu, you need to find the parameter responsible for the temperature setpoint (often indicated as SET or St). The value is changed using the navigation arrows. After making changes, be sure to confirm them, otherwise after a few seconds the system will return to the previous values. It is also worth checking the hysteresis parameter (d or Hys), which determines the temperature difference between turning on and off the compressor.
If the display case is equipped with a night mode function, set the timers for its activation. This will reduce energy consumption during non-working hours, reducing the intensity of the fans, but maintaining the coolness. Do not forget that in night mode the temperature can fluctuate within a wider range, so adding fresh products at this time is not recommended.
⚠️ Attention: Controller interfaces Dixell, Carel and Evco may differ. Always check the data sheet of a specific model before changing factory parameters, especially those related to the type of refrigerant or compressor power.
Calibrating readings and working with errors
A situation often arises when the display shows +4°C, and an independent thermometer shows +7°C. In this case, calibration or correction of readings is necessary. Most modern controllers have an "offset" or "calibration" parameter (often denoted as oF or Cal). By making changes to this parameter, you shift the entire reading scale.
For accurate calibration, use only a verified reference thermometer. Place it in the center of the chamber, in a glass of water (to simulate the heat capacity of the product), and leave it for several hours until the readings stabilize. Only after this make adjustments to the controller settings. Sharp jumps in readings may indicate a malfunction of the sensor itself.
What to do if the sensor is faulty?
If, when you tap the sensor or change the temperature in the chamber, the readings on the display do not change or show absurd values (for example, -99 or +99), most likely the thermistor has failed. Its resistance can be checked with a multimeter: at room temperature it should be about 10 kOhm (for most models).
Remember that the sensor can “drift” over time, that is, change its readings nonlinearly. Regularly, once every six months, checking display display readings using an external device is the best prevention of damage to goods. If the error exceeds the permissible standards even after calibration, the sensor must be replaced.
Environmental factors and their influence on temperature conditions
A refrigerated display case is not an isolated system; it actively interacts with the environment. The temperature in the sales area, the presence of drafts from air conditioners or open doors, direct sunlight - all this directly affects the operation of the equipment. If the room is hot, the compressor has to work harder, which can lead to a temporary increase in the temperature inside the chamber.
Ventilation The condenser also plays a critical role. If the radiator grille is clogged with dust or is pushed close to the wall, heat transfer is impaired. This leads to an increase in condensation pressure and a decrease in cooling efficiency. In such conditions, even the correctly adjusted temperature will not be maintained stably.
Air humidity is also important. If the air in the display case is too dry, the products will air out faster, and less frost may form on the evaporator, which will change heat transfer. At high humidity, the air ducts may freeze, which will block the access of cold air to the products.
Typical errors and methods for eliminating them
One of the most common errors is tightly loading the display case to the top, blocking the air ducts. Air circulation is disrupted, the cold does not reach the upper shelves, and the sensor located below gives false readings that it is “cold”. As a result, the product at the top deteriorates, and the compressor may freeze.
Another mistake is setting the temperature “by eye” without taking into account the heat flow from the freshly loaded product. If you load the display case with warm products, the temperature will rise sharply. Do not immediately turn the regulator to minimum: this will lead to freezing of the evaporator. It is better to wait until the system itself reaches the mode, or reduce the setpoint slightly.
- 🔴 Overflow: Loading above the “maximum load” line (MAX LOAD LINE) disrupts circulation.
- 🔴 No defrosting: Ignoring the defrost mode leads to the formation of an ice coat.
- 🔴 Incorrect placement: Installing the display cabinet closer than 30 cm to walls or heat sources.
Regular maintenance, including cleaning the condenser, checking door seals and monitoring the operation of fans, will help avoid most problems. If the display case no longer holds the temperature, check to see if an ice plug has formed in the drainage system, which is interfering with the flow of melt water.
How often should the display case be defrosted?
Most modern display cases have automatic defrosting, which is activated by a timer or compressor time counter. However, if you notice a layer of frost more than 3-5 mm thick on the back wall or a decrease in cooling efficiency, you must perform manual defrosting. On average, complete defrosting with washing is recommended to be carried out once every 3-6 months, depending on the humidity in the room and the intensity of use.
Why does the display case hum after setting the temperature?
Increased noise may be due to the fact that the compressor began to work more intensively due to a decrease in the temperature settings. Vibrations of the cabinet can also be a source of noise if the display case is not level. Check the leveling feet (feet) to ensure that the equipment is level. If the fan is humming, there may be ice frozen on its blades or the bearings need lubrication.
Can the display case be used as a freezer?
Absolutely not. The design of refrigerated display cases (insulation thickness, refrigerant type, compressor power, oil type) is not designed for temperatures below -5..-10°C. An attempt to set such a temperature will lead to failure of the compressor, since the oil will thicken and stop lubricating the rubbing parts, and the refrigerant will not be able to circulate effectively.