Effective operation of a retail outlet directly depends on the serviceability of cooling equipment. If the display case does not maintain the set mode, the products spoil, and sanitary inspections can result in a large fine. Adjustment of the display refrigerator is not just turning the thermostat knob, but a set of measures to set up the automation, check the refrigerant and calibrate the sensors.
Shop owners are often faced with a situation where the equipment hums, but does not freeze, or, conversely, turns vegetables into ice lumps. Temperature conditions must be stable, without sudden jumps, which are detrimental to most types of goods. In this article we will look at how to diagnose and configure the main components of the system.
Remember that intervention in the electrical circuit requires compliance with safety precautions. Before starting any work, you must disconnect the equipment from the network. Incorrect setting can lead to failure ⚠️ Attention: If you notice oil under the unit or hear gas hissing, self-adjustment is prohibited. You need to call a technician with equipment to refuel with freon. or failure of the compressor circuit tightness
⚠️ Attention: If you notice oil under the unit or hear gas hissing, independent adjustment is prohibited. You need to call a technician with equipment to refill with freon.
Diagnostics of current indicators and preparation
Before turning the adjustment screws, you need to understand the real state of affairs. A visual assessment by eye will not help here. You will need an external thermometer that fits inside the chamber. Standard thermostat Often shows data with an error, especially if the equipment has been in use for several years.
Place the control thermometer in the center of the work area, away from the walls and ventilation holes. Leave the equipment to operate as usual for 3-4 hours. This will allow the system to enter the operating cycle and show real values temperature gradient.
Record the readings at the moments when the compressor is turned on and off. The difference between these values shows the hysteresis system. If the spread is too large (more than 5-7 degrees), this is a signal of problems with heat transfer or a refrigerant leak.
Also check the integrity of the door seals. Even a microscopic gap will upset the balance, and no amount of electronic adjustment will help. Cold air is heavier than warm air, so it will constantly flow down, causing the unit to wear out.
Setting the thermostat and turbojet engine
The main control element in most models is thermostat (thermostat). In older models this is a mechanical device with a capillary tube, in new ones it is an electronic controller. The mechanical thermostat is adjusted by rotating the adjusting screw, often hidden under a seal or protective cap.
If your refrigerator is equipped with thermostatic valve (TRD), the situation becomes more complicated. The turbojet engine doses the supply of liquid refrigerant to the evaporator. Its setting affects the superheat of the vapor at the outlet of the evaporator. Incorrect adjustment of the turbojet engine leads either to “starvation” of the evaporator (lack of cold) or to water hammer in the compressor.
A special key is used to adjust the turbojet engine. Turning the stem clockwise increases the static pressure, raising the boiling point. Counterclockwise - lowers. This should be done in small steps, waiting for the cycle to stabilize for at least 20 minutes after each turn.
⚠️ Attention: The parameters of the turbojet engine depend on the type of refrigerant (R134a, R404A, R600a). Using settings intended for a different freon will cause damage to the compressor.
How to distinguish a mechanical thermostat from an electronic one?
The mechanical one has a scale with numbers (1-7) or snowflake patterns and clicks when switching. The electronic one is equipped with a display, buttons and shows the exact temperature in degrees Celsius. In mechanical models, adjustment is made with a screw, in electronic ones - through the settings menu.
Adjusting the defrost timer (Defrost)
Modern display cases operate in No Frost or static cooling mode with periodic defrosting. The defrost timer plays a key role here. It determines how often and for how long it will turn on Evaporator heating element to remove ice.
If the timer is set incorrectly, two scenarios are possible. If defrosting is too infrequent, the evaporator becomes overgrown with a “fur coat” that blocks the air flow. The cold stops flowing into the chamber, although the compressor hums continuously. If you defrost too frequently, you waste power and expose your food to heat stress.
A standard defrost cycle is usually set in the range of 6-8 hours of operation per 15-20 minutes of defrost. However, in summer, when indoor humidity is high, the intervals should be reduced. The setting is made either by mechanically turning the timer dial, or through a digital controller.
☑️ Checking the defrost system
It is important to check and defrost sensor. It should open the heating element circuit when the evaporator temperature reaches +10...+15°C. If the sensor is “stuck”, the heating element can heat constantly, which is dangerous due to fire or melting of plastic elements.
Calibration of electronic controllers
In professional equipment brands like Pole Cold, Carboma or River advanced controllers are often used (for example, Dixell, Eliwell). They allow you to set precise setpoint values. To enter the technical parameters menu, press and hold a specific key combination (often “Set” + “Down”).
In the menu you will find the parameters Set Point (target temperature) and Differential (differential). The differential is the temperature difference at which the compressor will turn on again after turning off. For example, with a setpoint of +4°C and a differential of 3°C, the compressor will turn off at +4°C and turn on at +7°C.
It is also worth paying attention to the delay parameter for turning on the compressor after defrosting. This prevents the engine from starting until the system pressure stabilizes. Typically this value is 3-6 minutes.
| Parameter | Description | Typical value | Units |
|---|---|---|---|
| St (Set Point) | Target temperature | +2...+6 | °C |
| Hy (Hysteresis) | On differential | 2...4 | °C |
| Id (Defrost Interval) | Interval between defrosts | 360 | min |
| Pd (Defrost Duration) | Duration of defrost | 20 | min |
Balancing air flows and loading
Even perfectly configured automation will not save if air circulation is disrupted. In shop windows, it is critically important not to block the ventilation grilles with goods. Air must circulate freely from the evaporator to the products and back. air curtain It is critical not to block the ventilation grilles with product. Air must circulate freely from the evaporator to the products and back.
There is the concept of “Load Line”. This is an imaginary limit above which goods cannot be raised. Exceeding this line destroys the air cushion, and cold air simply falls out into the sales area rather than cooling the products.
When adjusting, consider the type of product. Meat and fish require lower temperatures and stability than vegetables. Vegetables in sealed containers may suffocate or freeze if the cold setting is too aggressive.
⚠️ Attention: Do not place items directly on the bottom of the compartment or against the back wall. This blocks the exit of the drainage holes and disrupts the airflow, which leads to local areas of freezing.
Elimination of common malfunctions during adjustment
During the setup process, you may encounter situations that require repair rather than adjustment. For example, if the compressor runs around the clock, but the temperature does not drop below +10°C, most likely a problem has occurred. Adjusting the thermostat here is pointless - it simply does not allow the system to stop. freon leak. Adjusting the thermostat here is pointless - it simply does not allow the system to stop.
If the refrigerator often turns on and off (short cycle), check the thermostat contacts. They could burn or oxidize. Also, the cause may be an incorrectly set differential (too small).
Continuous formation of condensation on the glass or housing indicates problems with thermal insulation or operation in conditions of high humidity without appropriate adjustment of anti-condensation heaters.
To diagnose complex cases, use a multimeter. Check the resistance of the compressor windings and the integrity of the heating element circuit. The resistance standard of the heating element is usually from 200 to 400 Ohms, depending on the power.
Why did a whistle appear after adjustment?
A whistling sound after adjusting the turbojet engine or replacing the filter-drier may indicate the passage of the refrigerant through too narrow a cross-section or the presence of air in the system. Vacuuming and refilling are required.
How often do you need to adjust a display refrigerator?
Professional adjustment is required 1-2 times a year, usually