Refrigeration and air conditioning electronic expansion valve troubleshooting methods

1. Basic operating principles of refrigeration and air conditioning systems

First, the air conditioning compressor obtains power from the electric power system, compresses the low-temperature, low-pressure gaseous refrigerant into high-temperature, high-pressure gaseous refrigerant, and discharges it. Then these gases enter the condenser through sealed pipes, condense into medium-temperature, high-pressure liquid refrigerant, and flow into the dryer. It is dried, filtered, and then throttled and decompressed by the electronic expansion valve, it becomes low-temperature, low-pressure mist refrigerant and enters the evaporator. After absorbing a large amount of heat in the evaporator, it evaporates into low-temperature, low-pressure gaseous refrigerant and re-enters the compressor to start the next cycle. The entire working process is carried out over and over again to achieve the purpose of reducing the air temperature around the evaporator. At the same time, the evaporator fan serves as a ventilation device, blowing low-temperature air into the room to achieve the cooling effect, allowing indoor personnel to have a comfortable and refreshing environment, and keeping the equipment in a good operating environment.

2. Electronic expansion valve control principle Refrigeration systems generally use EXV electronic expansion valves to throttle medium-temperature and high-pressure liquid refrigerants and reduce their pressure to low-temperature and low-pressure mist refrigerants. The electronic expansion valve adjusts the evaporator liquid supply according to a preset program. Electronic expansion valves are divided into electromagnetic expansion valves and electric expansion valves. From the perspective of control implementation, electronic expansion valves are composed of three parts: controller, actuator and sensor. It adapts to the development requirements of refrigeration mechatronics, has excellent characteristics that thermal expansion valves cannot match, and provides conditions for intelligent control of refrigeration systems. The driving method of the EXV electronic expansion valve is that the controller calculates the parameters collected by the sensor and issues adjustment instructions to the drive board. The drive board outputs an electrical signal to the electronic expansion valve to drive the action of the electronic expansion valve. When shutting down, the main compressor will run for 10 seconds after the electronic expansion valve is completely closed; within 10 seconds of starting the main compressor, the electronic expansion valve will maintain the minimum opening. When the unit is running, the EXV electronic expansion valve will adjust the opening according to the set suction superheat value. The EXV electronic expansion valve will be prioritized by the operating status of the unit. 3. Analysis of the five major fault causes of electronic expansion valve 3.1 Temperature sensor failure. The layout of the temperature sensors is shown in the figure below, where T1 is the evaporator circulating water outlet temperature sensor, T2 is the evaporator circulating water return water temperature sensor, and T6 is the evaporator refrigerant inlet temperature sensor. Temperature sensor short circuit, open circuit and sensor resistance drift will cause abnormal adjustment of the electronic expansion valve.