Rapid temperature change test chamberReason 1: Ice blockage

【 Cause 】: If the refrigerant contains a high amount of water, it may freeze at the throttle of the thermal expansion valve when the evaporation temperature drops below 0 ℃, causing 'ice blockage'. Possible reasons for ice blockage include: 1) Insufficient vacuum pumping time of the system, which failed to completely remove the moisture in the pipeline. 2) Excessive moisture in the refrigerant or lubricating oil added to the system.

【 Location 】: Ice blockage usually occurs at the throttle hole of the expansion valve, as this is the location with the smallest temperature and aperture in the entire system. Observing the color of the test paper on the sight glass can determine whether there is too much water in the refrigerant.

【 Solution 】: Replace the dry filter and remove the moisture in the system pipeline; If necessary, it is necessary to evacuate and refill the refrigerant.

Reason 2: Dirty blockage

【 Cause 】: Impurities exist in the system.

The sources of impurities in the refrigeration system include: oxide film that is not completely removed during copper pipe welding, metal shavings generated by compressor wear and tear, and substances produced by chemical reactions of refrigeration oil.

【 Location 】: Generally, dirty blockage occurs at the dry filter, where impurities in the system are intercepted by the filter, causing dirty blockage; It may also occur at the throttle hole of the expansion valve. After a dirty blockage occurs, the evaporation pressure of the system decreases, the return air temperature increases, the degree of superheat increases, and it is difficult for the system to return oil.

[Solution]: For blockages that occur at the drying filter, the drying filter needs to be replaced. If there is dirt or blockage at the flow port of the expansion valve, the split type expansion valve can remove the flow port component and clean it carefully; The integral expansion valve needs to be replaced.

Rapid temperature change test chamberReason 3: Leakage of filling medium in the temperature sensing package

【 Cause 】: If the filling medium inside the temperature sensing bag leaks, the power to open the expansion valve above the diaphragm will be lost, causing the expansion valve to partially or completely close and the system low pressure to be very low. The usual causes include:

1) The capillary tube of the temperature sensing package is broken.

The capillary rupture causes the filling medium inside the temperature sensing package to leak, resulting in the inability to transmit the correct signal to the actuator of the thermal expansion valve. The possible locations of fracture include the connection between the temperature sensing bulb and the capillary tube in the capillary tube, as well as the welding point between the capillary tube and the valve body cover.

2) Temperature sensing package and capillary corrosion.

If there are a large number of highly corrosive substances in the application environment, they can all damage the passivation layer on the surface of stainless steel, thereby accelerating the corrosion of the metal. At the same time, there are a large number of solid particles in the atmospheric environment, which may also cause pitting corrosion on the metal surface under the solid particles when they interact with sulfur dioxide and water. In addition, the corrosion rate is also related to relative humidity and temperature.

3) Damage to the capillary tube of the temperature sensing package.

Sharp objects scraping, cutting, squeezing, or burning the capillary tube can cause the filling medium inside the temperature sensing package to leak or block the capillary tube, affecting the transmission of overheating signals to the upper chamber of the diaphragm, thereby causing the expansion valve to malfunction.

[Solution]

In this situation, it is necessary to replace the expansion valve. Therefore, it is particularly required to avoid contact between the capillary tube and sharp objects during installation and use, to prevent damage and burns, and to use protective materials to protect the capillary tube. For point corrosion phenomena, protective layers and corrosion inhibitors can be used to control the concentration of corrosive gases and solid particles in the atmospheric environment.

Rapid temperature change test chamberReason 4: The installation position of the temperature sensor is incorrect.

It is recommended to install the temperature sensor horizontally on the return pipe near the evaporator outlet. During installation, the temperature sensing package needs to be fixed with an installation strap, and the surface of the return pipe should be derusted. If it is a steel pipe, the surface should be derusted and coated with silver paint to ensure good contact between the temperature sensing package and the return pipe.

Reason 5: The temperature sensor failed to accurately sense the temperature.

The temperature at the temperature sensing bulb is affected by other factors. Perceived temperature lag and difficulty in heat transfer caused by dirt.

Reason 6: Migration of filling medium (with MOP function)

For expansion valves with MOP function, the amount of filling medium filled at the temperature sensing bulb and valve head is relatively small. If the temperature of the valve head is lower than that of the temperature sensing bulb, the filling medium will also migrate from the temperature sensing bulb to the valve head, resulting in the expansion valve not working properly. The process of migration of the filling medium is related to temperature difference and time.

[Solution]: During transportation, storage, installation, debugging, and use, the temperature of the temperature sensing package should always be kept lower than that of the temperature sensing element. If the migration of the filling medium has occurred, the filling medium can be returned to the temperature sensing chamber by cooling the temperature sensing chamber (recommended) or heating the valve head. This process is affected by temperature differences and time.

Rapid temperature change test chamberReason 7: The valve core is stuck

【 Cause 】: The refrigerant in the system contains a high amount of water or corrosive substances, causing severe corrosion inside the expansion valve, resulting in the valve core being unable to move and the expansion valve being unable to adjust.

[Solution]: Replace the expansion valve and drying filter to remove moisture and other impurities from the system.

Reason 8: The capacity of the selected expansion valve is too small, and the superheat adjustment is improper.

: There is a phenomenon of liquid return; Low superheat; Inhalation temperature and pressure fluctuations.

【 Cause 】:

1) The valve core of the thermal expansion valve is stuck.

2) External balance tube blockage. The sensed pressure cannot be quickly transmitted to below the diaphragm, resulting in a small closing force and a large opening of the valve port. Source of this article: Refrigeration Encyclopedia official account

3) Installation issue with temperature sensing package. Incorrect installation position and method, or poor contact and insulation, may all cause excessive liquid supply.

4) The selected expansion valve has excessive cooling capacity.

5) Improper adjustment of superheat degree of thermal expansion valve