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The refrigeration system has a failure, and the operating status of the system is generally understood by looking, listening, and touching. When the operating pressure and temperature of the system exceed the normal range, in addition to the deterioration of indoor and outdoor temperatures, there must be problems, which is an important basis for judging the source of the fault.
1. Detection of pressure and temperature of refrigeration system
Pressure of the refrigeration system: the refrigeration system can be divided into two parts, high and low pressure during operation. The high-pressure section is called the high-pressure pressure from the compressor discharge port to the throttle valve. The suction port pressure of the compressor is called the suction pressure, and the suction pressure is close to the evaporation pressure. The difference between the two is the flow resistance of the pipeline.
For convenience, the evaporating pressure and condensing pressure of the refrigeration system are detected at the suction and exhaust ports of the compressor. That is usually called the suction and discharge pressure of the compressor. The purpose of detecting the suction and exhaust pressures of the refrigeration system is to obtain the evaporation temperature and the condensation temperature of the refrigeration system, so as to obtain the operating condition of the refrigeration system.
Temperature in the refrigeration system: The temperature in the refrigeration system involves a wide range, including evaporation temperature, suction temperature, condensation temperature, exhaust temperature, etc. What determines the operating conditions of the refrigeration system are the evaporation temperature and the condensation temperature.
Evaporation temperature: refers to the temperature at which the liquid refrigerant boils and vaporizes in the evaporator. Example: The evaporating temperature of the air conditioning unit is 5 ~ 7 degrees as the optimal evaporating temperature of the air conditioning unit, that is, the design evaporating temperature of the air conditioning unit is between 5 ~ 7 degrees. If it is not between 5 ~ 7 degrees, you should find out the reason.
And the evaporation temperature cannot be directly detected, only the evaporation temperature can be obtained by detecting the corresponding evaporation pressure, by referring to the refrigerant saturation temperature pressure comparison table. A comparison table of the saturation temperature and pressure of commonly used refrigerants is freely available in our refrigeration encyclopedia public account, and the necessary partners can be obtained for free in the public account menu.
Condensation temperature: the temperature at which the superheated vapor of the refrigerant condenses into a liquid after releasing heat in the condenser. The condensing temperature cannot be directly detected, only by detecting its corresponding condensing pressure, and then by referring to the refrigerant saturation temperature and pressure comparison table. Condensation temperature is high, and its condensing pressure is relatively high, and they correspond to each other. Condensing temperature is too high, the load of the unit is heavy, and the motor is overloaded, which is unfavorable for operation. Its cooling capacity decreases accordingly and power consumption rises, and it should be avoided as much as possible.
Exhaust temperature: refers to the temperature of the compressor exhaust (including the temperature of the exhaust port). There must be a temperature measuring device to detect the temperature of the exhaust gas. Generally, small computers are not set up. The temporary measurement can be detected with a semiconductor point thermometer, but the error is large. The exhaust temperature is affected by the suction temperature and the condensation temperature. When the suction temperature or the condensation temperature increases, the exhaust temperature also increases accordingly. Therefore, the suction temperature and the condensation temperature must be controlled to stabilize the exhaust temperature.
Suction temperature: refers to the gas temperature of the compressor suction connection. A temperature measurement device is required to detect the suction temperature. Generally, small units do not have a temperature measurement device, and are generally estimated by hand touch during maintenance and debugging. The suction temperature of the air-conditioning unit generally needs to be controlled at about 15 degrees. Exceeding this value has a certain effect on the cooling effect.
Second, the influence of suction pressure change refrigeration system
Factors of low suction pressure: The suction pressure is lower than normal. The factors include insufficient cooling capacity, small cooling load, small expansion valve opening, low condensing pressure (referring to capillary system), and unsmooth filters.
Factors of high suction pressure: The suction pressure is higher than normal. The factors include excessive refrigerant, large cooling load, large opening of expansion valve, high condensing pressure (capillary system) and poor compressor efficiency.
Third, the impact of exhaust (condensation) pressure changes on the refrigeration system
Factors of high exhaust pressure: When the exhaust pressure is higher than the normal value, there are generally small cooling medium flow or high cooling medium temperature, excessive refrigerant charge, large cooling load, and large expansion opening.
Factors of low exhaust pressure: The exhaust pressure is lower than normal. The factors include low compressor efficiency, insufficient refrigerant quantity, small cooling load, small expansion valve opening, and unsmooth filter, including expansion valve filter and cooling medium The temperature is low.
4. Relationship between suction temperature and exhaust temperature
Actually, the exhaust temperature of the system is closely related to the intake temperature. As the intake temperature rises, the exhaust temperature also rises relatively, and vice versa. Knowing their relationship, you can master and control them well, and make the refrigeration system run better.
Fifth, the impact of compression and condensation unit temperature changes on the refrigeration system
Influence of exhaust temperature: In summer, the exhaust temperature of the compressor is relatively high and cannot be touched by hands. According to national standards, the exhaust temperature of the R22 refrigeration system should not exceed 150 degrees. Exceeding this temperature line is abnormal.
Exhaust gas temperature is too high: it is caused by the compressor suction temperature is too high, or the condensation temperature is too high, must pay attention. The exhaust temperature is too low, and the exhaust pipe is not touched by hand, which means that the intake temperature is particularly low, and the compressor may run on a wet stroke or in an operating state with relatively little working fluid. The wet stroke of the compressor is easy to damage the valve structure; the operation of the refrigerant in rare cases will affect the cooling of the motor windings and accelerate the aging of the insulating material.
The effect and reason of the high temperature of the cabinet: The surface temperature of the cabinet exceeds the normal range, mainly because the suction temperature of the refrigeration system is too high (above 15 degrees). Excessively hot steam enters the compressor and absorbs the heat in the casing, making the temperature of the steam higher, thereby increasing the temperature of the casing. The temperature of the superheated steam rises very high, and the temperature of the casing also rises very high, which is unfavorable for the cooling of the oil. This will affect the lubrication of moving parts, accelerate wear, and seriously cause the bearing to hold the shaft (bite). It will also cause the exhaust temperature to rise.
The effect and reason of the low temperature of the casing: the surface temperature of the casing is lower than the normal range, the reason is that the suction temperature is too low (below 15 degrees). It is beneficial to the cooling of refrigeration oil and motor windings, but the cooling capacity has decreased. When the suction temperature is particularly low, most of the casing will be condensed, and there is a danger of liquid blow. This is a fatal blow to the compressor, and special attention should be paid. At the same time, a large amount of refrigerant is dissolved in the refrigeration oil, which is not conducive to the lubrication of moving parts.
The temperature of the capillary tube: Under normal circumstances, the capillary tube is cold with dew, and there is a sound of liquid flowing. Under abnormal conditions:
1. The surface is very cold and dew condensation, but the flowing sound is loud, the reason is that the refrigerant is insufficient;
2. The surface is neither cold nor dew, and no flowing sound can be heard. The reason is clogged filter or capillary.
The temperature of the evaporator: under normal circumstances, the outer surface of the evaporator is very cold, and its condensed water droplets continue to drop. The temperature of the inlet and outlet winds is relatively large, usually 12 to 14 degrees. , There is not much dew, or no condensation, you can hear the sound of refrigerant flowing very loudly, and the temperature difference between the inlet and outlet air is small. The reason is that the amount of refrigerant is insufficient, or the opening degree of the expansion valve is small.
Ambient temperature requirements of outdoor unit: According to national standards, the outdoor unit is at an ambient temperature below 35 degrees Celsius, the air conditioning unit should ensure normal operation, and can reach the cooling capacity marked on the product nameplate and other indicators. When the ambient temperature is in the range of 35 ~ 43 degrees, the air conditioning unit can run, but it cannot guarantee the cooling capacity marked by its chrome brand. It is already running at full load. This is because the condensation temperature, pressure, and exhaust temperature are quite high. If the heat of the indoor unit is large, the electronic control protector may act, cut off the power, and stop running. When the outdoor temperature exceeds 43 degrees, the air conditioning unit is in overload operation, which will cause the action of the electronic control protection device, cut off the power, and stop the operation.
Indoor air-conditioning temperature requirements: indoor normal constant temperature value should not exceed 30 degrees as well. If operating at temperatures exceeding 30 degrees Celsius, the air conditioning unit may be operating under overload conditions, the condensation temperature and exhaust temperature of the refrigeration system will rise, it may also cause the electrical protector to act, cut off the power supply, and the operating life of the air conditioning unit unfavorable.
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