Refrigeration basics: electronic expansion valve, four-way valve, solenoid valve

1、Electronic expansion valve

Electronic expansion valve is a kind of precision control element, mainly composed of coil part and valve body part. The coil part includes stator and rotor, in which the stator generates a magnetic field, the rotor rotates under the action of the magnetic field, which drives the valve needle to move up and down, realizing the adjustment of refrigerant flow. The valve part mainly includes stainless steel shell, magnet rotor, nut, screw shaft, needle valve, body and connecting tube, etc., of which the needle valve is designed as a cone, in order to accurately control the opening of the valve port. In order to prevent refrigerant leakage, the electronic expansion valve is also equipped with bellows, which is used to isolate the moving part of the spool from the refrigerant.

The operating principle of the electronic expansion valve is based on an electromagnetic or stepper motor drive. The controller receives signals from temperature and pressure sensors, and after calculation, outputs a pulse width modulation (PWM) signal to the stepper motor or electromagnetic coil, which drives the valve needle up and down, thus changing the size of the valve opening, and realizing the precise control of the amount of refrigerant entering the evaporator.

Normal electronic expansion valve: after plugging in the “click” sound. If there is no sound, or in refrigeration expansion valve in the compressor work after the beginning of frost, it should be detected whether the coil and power supply is normal (12V pulse power). If the voltage is normal, the computer board is normal, if there is no sound in the expansion valve at this time, the expansion valve is bad, this time the first measurement of the electronic expansion valve coil DC resistance, if normal, it may be the valve body dirty blocking, available high-pressure gas blowing.

In addition, the electronic expansion valve should be reset when the power is off, then you can listen to the sound or feel whether the vibration to determine whether the valve needle is a problem. In the shutdown state, the valve spool is generally in the maximum degree of opening, then disconnect the coil lead, and then boot operation, if the refrigerant can not be passed at this time, you can determine the valve needle stuck. Under normal circumstances, touch the ends of the electronic expansion valve, the inlet is warm, the outlet is cool.

2, four-way valve

Four-way valve is an indispensable part of the refrigeration and air conditioning system, mainly used in heat pump air conditioners to change the direction of flow of refrigerant, to achieve the switch between refrigeration and heating mode. It consists of two parts: the electromagnetic guide valve and the main valve, which control the flow direction of refrigerant through the energization and de-energization of the electromagnetic coil, so as to achieve the function switching in different modes. The four-way valve mainly consists of: electromagnetic guide valve; main valve; guiding capillary tube and other components.

String gas diagnosis method - “touch”: whether it is refrigeration or heating mode, string gas is the cold suction pipe is not cold, the hot exhaust pipe is not hot. Available temperature testing instruments for suction (rated refrigeration mode 5 ~ 15 ℃), exhaust (rated refrigeration mode 60 ~ 90 ℃) of the temperature difference; if the error is not obvious that the four-way valve string gas, if there is no temperature measuring instruments, you can use your hand to “touch” method to identify.

Card dead diagnostic method - “listen”: at work, gently rotate the coil, listen to whether there is a “squeak” electromagnetic noise indicates that the solenoid coil is basically not a problem, if there is no obvious commutation suction when changing direction, “boing boing”, “boing boing”, “boing boing”, “boing boing”, “boing boing”. “Boing Boing” sound, indicating that the four-way valve may be stuck. Can be a small stick gently tapping, observe whether it can be restored.

Coil diagnostic method - “test”: usually four-way valve solenoid coil supply voltage is 220V AC power supply, you can first measure the coil voltage on both sides of the normal, and then use a multimeter solenoid coil resistance value is normal.

3, solenoid valve

Solenoid valve is a cold storage, air conditioning, water heating and other refrigeration equipment inside the very important parts, solenoid valves in the refrigeration system plays a role in controlling the fluid on and off, the common failure is not open or shut down, solenoid valves common faults are shown below.