1. Shut down. Insert the probe of the digital thermometer into the insulation layer at the return port of the evaporator (corresponding to the position of the temperature sensing bulb). Connect the pressure gauge to the tee of the compressor low pressure valve.
2. Turn on. Let the compressor run for more than 15 minutes to enter a stable operation state, so that the pressure indicator and temperature display reach stable values.
3. Adjustment. When adjusting the flow rate, it needs to be carried out in the normal operation of the refrigeration system, and it must be operated slowly and adjusted gradually. The judgment basis for adjusting the size of the liquid supply flow is as follows:
A. If the expansion valve body is completely frosted, it indicates that the flow rate is too small and large, and it should be increased;
B. If there is no change in the shape of the frosting when it is enlarged, the orifice of the expansion valve may be partially blocked and should be cleaned;
C. If the expansion valve body only has frost on the outlet side, it indicates that the flow rate is too large and should be adjusted down;
D. If the outlet side and lower part of the expansion valve body are frosted obliquely at 45°C, the inlet side should not be frosted, indicating that the adjustment is accurate and appropriate;
E. If only the inlet side of the expansion valve body is frosted, it indicates that the filter screen at the inlet of the valve body is blocked and should be cleaned;
F. If the expansion valve body is completely frost-free, it indicates that there is no flow. It is possible that the refrigerant has leaked out or the stop valve in the pipeline has not been opened or the capillary of the expansion valve temperature probe is leaking or the expansion valve orifice is blocked or the valve body inlet is filtered. The net part is blocked and should be cleaned.
Under normal circumstances, the expansion valve is very quiet when it is working. If there is a more obvious "silk" sound, it means that the refrigerant in the system is insufficient.
4. Temperature measurement. Use a thermometer to measure the difference between the temperature of the return air pipe and the evaporation temperature (that is, the actual superheat) and check the standard superheat (between 5-8°C) to determine whether the adjustment is appropriate. Use the suction pressure of the compressor as the saturation pressure in the evaporator, and look up the table to get the approximate evaporating temperature. Use a thermometer to measure the temperature of the return air pipe to see if it is within the normal range of 5-8°C compared with the evaporation temperature. The suction pressure value and the return pipe temperature must be read at the same time, otherwise the actual superheat calculated will be inaccurate.
Do not use rapid adjustment with large fluctuations during adjustment, so that the refrigeration system can run unstable and the effect of adjustment cannot be grasped. The loose gear type uses a small gear to drive a large gear, and the number of adjustment turns is relatively large, generally 2-4 turns; the pressure lever type has a relatively small number of adjustable turns, which is adjusted 1/4 turn each time; Adjust 1/2, 1/3, 1/4 circle.
Adjusting the expansion valve must be done carefully and patiently, and adjusting the pressure must take a time course. Every time the expansion valve is adjusted, it usually takes 15-30 minutes to stabilize the adjustment pressure of the expansion valve on the suction pressure gauge. In addition to observing the changes in the low-pressure pressure value, it is also necessary to observe the frosting at the expansion valve body, the evaporator coil and the compressor suction pipe to determine whether the adjustment is appropriate.
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