Causes of abnormal temperature/pressure of compressor suction and discharge.

First,why the compressor suction temperature is too high?

The compressor suction temperature is too high, which is mainly caused by the increase of suction superheat. Note that high suction temperature does not mean high suction pressure, because suction is superheated steam. Under normal circumstances, the compressor cylinder head should be half cold and half hot.

If the suction temperature is too high, the cylinder head will all heat up.

If the suction temperature is higher than normal, the exhaust temperature will also increase accordingly.

①The refrigerant charge in the system is insufficient, even if the expansion valve is opened to the maximum, the liquid supply will not change, so that the refrigerant vapor will overheat in the evaporator and the suction temperature will increase. Generally, there is a lack of refrigerant. Check the leakage point and add refrigerant to solve the problem.

②The opening of the expansion valve is too small, resulting in insufficient circulation of refrigerant in the system, less refrigerant dosage entering the evaporator, and high superheat, resulting in high suction temperature. Generally, it is necessary to control the resistance deviation of the temperature sensing bulb of the electronic expansion valve, or the copper tube at the temperature measuring position is blocked, so the temperature sensing bulb with the same resistance can be replaced.

③The filter screen of the electronic expansion valve is blocked, the liquid supply in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the suction temperature is increased. Excessive suction temperature caused by other reasons, such as poor heat insulation of return air pipeline or too long pipeline, can cause excessive suction temperature. Disassemble the pipeline, clean up the blocked position, redo the system, and then debug the equipment.

Second, why the compressor suction temperature is too low?

The low suction temperature is mainly caused by the low suction superheat caused by the large liquid supply of evaporator. The compressor suction temperature is too low for the following reasons:

①Too much refrigerant charge, for example, the multi-line will report that the exhaust temperature is too low for protection, which may be because it occupies part of the volume in the condenser and makes the condensation pressure increase, and the liquid entering the evaporator will increase accordingly. The liquid in the evaporator can not be completely gasified, which makes the gas sucked by the compressor contain liquid droplets. In this way, the temperature of the return air pipeline drops, but the evaporation temperature does not change because the pressure does not drop, and the superheat degree decreases. There is no significant improvement even if the expansion valve is turned down.

② The opening of electronic expansion valve is too large. Due to the loose binding of the temperature sensing element, the small contact area with the air return pipe, or the fact that the temperature sensing element is not wrapped with thermal insulation material and its wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate and close to the ambient temperature, which increases the opening of the expansion valve and leads to excessive liquid supply.

Third, the compressor exhaust temperature is not normal

The compressor discharge temperature can be read from the thermometer on the exhaust pipe. It is related to the adiabatic index, compression ratio and suction temperature of refrigerant. The main reasons for the increase in exhaust temperature are:

①The higher the suction temperature, the higher the exhaust temperature of refrigerant vapor after compression; As the condensation temperature rises, the condensation pressure will be higher, resulting in an increase in the exhaust temperature.

②The exhaust valve plate is shattered, high-pressure steam is repeatedly compressed and the temperature rises, the cylinder and cylinder head are hot, and the thermometer on the exhaust pipe also rises.

③The actual factors that affect the exhaust temperature rise are: low intermediate cooling efficiency, or excessive scale in the intercooler affects heat transfer, so the suction temperature of the later stage will inevitably be high, and the exhaust temperature will also rise.

④The air valve leaks and the piston ring leaks, which not only affects the exhaust temperature, but also changes the interstage pressure. As long as the compression ratio is higher than normal, the exhaust temperature will rise. In addition, water-cooled machines, lack of water or water will increase the exhaust temperature. Abnormal condensation pressure and reduced exhaust pressure.

Fourth, the exhaust pressure is high

The high exhaust pressure is mainly caused by the high condensation pressure, not the compressor itself. The exhaust pressure generally corresponds to the condensation temperature. Under normal circumstances, the discharge pressure of the compressor is very close to the condensation pressure. High exhaust pressure will increase the compression work and decrease the gas transmission coefficient, thus reducing the refrigeration efficiency.

Main reasons for high exhaust pressure:

★The flow of cooling water (or air) is small and the temperature is high;

★There is air in the system, which increases the condensation pressure;

★When the refrigerant charge is too much, the liquid occupies the effective condensation area;

★The condenser is in disrepair for a long time, and the fouling on the heat transfer surface is serious, which can also lead to the increase of condensation pressure. The existence of scale also has a great influence on condensation pressure.

Fifth, the exhaust pressure is too low

The low exhaust pressure is mainly caused by the small or even stopped refrigerant flow in the pipeline of refrigeration system. The exhaust pressure is too low, although the phenomenon is manifested in the high-pressure end, but the reason is mostly produced in the low-pressure end. The main reasons for the low exhaust pressure are the ice blockage or dirty blockage of the expansion valve and the blockage of the filter, which will reduce the suction and exhaust pressures.