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What are the common faults and diagnostic methods for electronic expansion valves and four-way valves

November 16,2023

I. Four-way Valve

The four-way valve, also known as an electromagnetic four-way reversing valve, is an important component of air conditioning systems that mainly switches between cooling and heating. The following methods can be used for diagnosing gas bypassing in the four-way valve:

"Touch": In both cooling and heating modes, gas bypassing occurs when the suction pipe that should be cold isn't cold and the discharge pipe that should be hot isn't hot. The temperature difference between suction (5-15°C in rated cooling mode) and discharge pipes (60-90°C in rated cooling mode) can be measured with a temperature testing instrument. If the error is not obvious, it may indicate that the four-way valve is bypassing. If there is no temperature measuring instrument, the diagnosis can be made by touching with hands.

"Listening": When the coil is working, rotate it gently and listen for any "squeaking" electromagnetic noise, which indicates that the electromagnetic coil is generally fine. If there is no obvious switching sound during the reversing process, it may indicate that the four-way valve is stuck. It can be lightly tapped with a wooden stick to observe if it can recover.

Coil diagnosis method - "Measure": The voltage supplied to the electromagnetic coil of the four-way valve is usually AC 220V power. First, measure whether the voltage at both ends of the coil is normal, and then use a multimeter to measure the resistance value of the electromagnetic coil to determine if it is normal.

未命名

HONGSEN HVAC SPF Electronic Expansion Valve

II. Electronic expansion valve

The  electronic expansion valve  is a throttling element that can enter the refrigerant flow of the refrigeration system according to a preset program. In some cases where the load changes dramatically or the operating conditions vary widely, traditional throttling elements (such as capillary tubes, thermal expansion valves, etc.) cannot meet the requirements of comfort and energy efficiency. The electronic expansion valve combined with compressor capacity modulation technology has been increasingly widely used. Current research on electronic expansion valves roughly includes three aspects: application research, flow characteristics, control strategies, and algorithms.

A normal electronic expansion valve produces a "clicking" sound when plugged in. If there is no sound or the valve begins to frost after the compressor starts working during refrigeration, its coil and power supply should be checked (12V pulse). If the voltage is normal, it indicates that the computer board is normal. If there is no sound inside the expansion valve at this time, it may be a faulty valve. First, measure the DC resistance of the electronic expansion valve's coil. If it is normal, it may be dirt blocking the valve body, which can be cleaned using high-pressure gas.

In addition, when the power is turned off, the electronic expansion valve should reset. The valve needle can be checked for problems by listening for sound or feeling vibration. When the air conditioner is turned off, the valve core is generally in the fully open position. At this time, disconnect the coil lead and run the machine. If the refrigerant cannot pass through, it can be judged that the valve needle is stuck. Under normal circumstances, touch the two ends of the electronic expansion valve with your hand, and the inlet is warm while the outlet is cold.

Common Faults of Electronic Expansion Valve

The valve of the electronic expansion valve is fully closed. Analysis and repair: Normally, before the electronic expansion valve is powered on, the needle valve is in the open position. The valve opening degree is 480 pulses when it leaves the factory. However, due to the vibration during transportation, the position of the rotor may change, causing the valve to be fully closed. In the event of this fault, perform a reset operation after powering on to ensure that the valve body is in an open state. Only then can the flow rate be adjusted by controlling the size of the needle valve opening with a stepper motor based on the pulses sent by the electronic control board.

There is noise inside the electronic expansion valve after it starts up. Analysis and repair: If the noise is too loud, it indicates that the internal components are stuck and need to be replaced entirely. It is worth noting that if there is a "clicking" sound inside the valve body when the power is turned on, this is normal. After the air conditioner is powered on, the electronic control panel will send a pulse for the electronic expansion valve to fully open or close. At this time, when the rotor of the electronic expansion valve rotates to the maximum opening degree, it collides with the limit device, making a "clicking" frictional sound. When the air conditioning system is filled with refrigerant, the resistance to rotor movement increases, and the way sound is transmitted changes, making the sound of the electronic expansion valve's operation much quieter.

The electronic expansion valve does not move. Analysis and repair: When the power is turned on, first listen for any "clicking" sound inside the valve body. If there is none, check whether the valve body is completely inserted into the coil, whether the coil is properly connected to the circuit board, and whether the coil power supply voltage meets the requirements (12V±1.2V). If all of the above checks are normal, check whether the valve body can be fully opened. If it cannot, it means that the valve body is faulty and needs to be replaced. If the valve body can be fully opened, check whether the number of pulses for full closure is less than 480pps. If so, check the driving mechanism.

The electronic expansion valve is stuck. Analysis and repair: This fault is caused by foreign objects entering the electronic expansion valve during refrigerant flow and accumulating inside the valve body. When debris is embedded in the valve body, it increases the frictional force of the rotor movement, causing the valve to be stuck. Usually, only a complete replacement can solve this problem. Common debris includes foreign objects in the pipeline and welding oxides, which are mostly caused by human factors. To prevent this fault, you should increase pipeline cleanliness during maintenance, use welding protection, and generally inject chlorine gas to reduce oxides. Also, 100-mesh or higher filters should be installed at both ends of the valve body. When welding the electronic expansion valve, immerse the entire valve body in water and use nitrogen gas for protection during welding. To prevent the nitrogen gas from being heated to high-temperature gas and damaging the electronic expansion valve by passing through the valve stem, nitrogen gas must be filled simultaneously from the inlet and outlet of the expansion valve.


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