Working Principle and Fault Handling of Electronic Expansion Valve

1、 Working principle of electronic expansion valve

In the variable frequency air conditioning refrigeration system, the opening size of the electronic expansion valve is accurately controlled based on changes in microprocessor circuit program, compressor operating frequency, operating current, refrigeration system operating pressure value, and sensor sensing temperature value, and the optimal refrigerant flow rate is adjusted to ensure the optimal operation of the air conditioning.

The common end of the electronic expansion valve and 2, 3, 4, 5, and normal are all 44 Ω. The common terminal is connected to 12V, and the remaining 4 are connected to the CPU control circuit. When the power is cut off, the electronic expansion valve should be reset. At this time, the problem with the valve core can be determined by hearing a "click" sound and feeling whether it is vibrating. Attention! This is an example of a coil from a certain manufacturer. The wire colors from other manufacturers may be inconsistent, but the common end is uniformly located at the very edge. A multimeter needs to be used on site to search for the common end.

In the shutdown state, the valve core is generally at its maximum opening. If the coil plug is unplugged and the refrigerant cannot pass through, it can be determined that the valve core is stuck. Under normal circumstances, there is a "clicking" sound when starting or stopping the refrigeration system. When touching the two ends of the electronic expansion valve, the inlet is warm and the outlet is cold.

2、 Common faults of electronic expansion valves

Fault phenomenon 1: The valve of the electronic expansion valve is in a fully closed state.

Analysis and maintenance: Normally, the electronic expansion valve is in the open position before being energized. When the valve body leaves the factory, the valve opening is 480 pulses, but due to the rotor being fixed through a threaded structure, the position of the rotor may change during transportation due to vibration, ultimately causing the valve to be in a fully closed state. When encountering this fault, a reset operation can be performed after powering on to ensure that the valve body is in an open state, so that the size of the needle valve opening can be controlled by a stepper motor to adjust the flow rate of the expansion valve.

Fault phenomenon 2: After starting up, there is noise inside the electronic expansion valve.

Analysis and maintenance: If the noise is too loud, it indicates that the internal components are stuck and need to be replaced as a whole to solve the problem. It is worth mentioning that if there is a "click" sound inside the valve body when the power is turned on, it is a normal phenomenon. After the air conditioning is powered on, the electronic control board will send a fully open or fully closed pulse to the electronic expansion valve. At this time, when the rotor of the electronic expansion valve turns to its maximum opening, it collides with the limit device and emits a "clicking" friction sound. When the air conditioning system is filled with refrigerant, the resistance to rotor rotation increases, and the transmission mode of sound changes, the action sound of the electronic expansion valve will become very small.

Fault symptom 3: The electronic expansion valve does not operate.

Analysis and maintenance: When connecting the power supply, first listen for a "clicking" sound inside the valve body. If not, check whether the valve body is fully inserted into the coil, whether the connection between the coil and the circuit board is normal, and whether the coil power supply voltage meets the requirements (12V ± 1.2V). If all the above checks are normal, check if the valve body can be fully opened. If not, it indicates that the valve body is damaged and needs to be replaced. If the valve body can be fully opened, check whether the pulse number of fully closed valve is greater than 480pps. If it is less than 480pps, check the driving mechanism.

Fault phenomenon 4: The electronic expansion valve is stuck.

Analysis and maintenance: This fault is due to debris entering and accumulating inside the electronic expansion valve during the flow of refrigerant. If debris is embedded in the valve body, it will increase the friction force of the rotor rotation, causing jamming. Usually, only an overall replacement can solve the problem.

Common impurities include foreign objects in pipelines, welding oxides, etc., indicating that faults are often caused by human factors. To prevent this fault from occurring, during maintenance, one is to strengthen the cleanliness of the pipeline, the other is to adopt welding protection, generally using the method of injecting chlorine gas to reduce oxides, and the third is to install filters with a mesh size of 100 or more at both ends of the valve body.