4-way Reversing Valve fault identification and cause analysis

One. Structure and use of four-way valve

The four-way valve consists of three parts:

• pilot valve
• main valve
• solenoid coil

The solenoid coil can be removed. The pilot valve and the main valve are welded together.

A brief introduction to the working principle of the four-way valve:

When the electromagnetic coil is in a power-off state, as shown in the figure below: the pilot slide valve ② moves to the right under the drive of the compression spring ③, and the high-pressure gas enters the capillary tube ① and then enters the piston cavity ⑤. On the other hand, the gas in the piston cavity ④ is discharged. There is a pressure difference, the piston and the main slide valve ⑥ move to the right, so that the E and S pipes are connected, and the D and C pipes are connected, thus forming a refrigeration cycle as shown in the figure.

When the solenoid coil is energized, as shown in the figure below, the pilot spool valve ② overcomes the tension of the compression spring ③ and moves to the left under the action of the magnetic force generated by the solenoid coil. Due to the pressure difference between the two ends of the piston, the piston and the main slide valve ⑥ move to the left, so that the S and C pipes are connected, and the D and E pipes are connected, thus forming a heating cycle.

Two, four-way valve reversing fault identification

1. Intermediate flow: It is not difficult to find from the structure of the four-way valve. When the main slide valve is in the middle position, as shown in the figure below, the three pipes E, S and C are connected with each other, and there is a certain intermediate flow. At this time, the compressor is high pressure. The refrigerant in the tube can flow directly back to the low pressure tube. The purpose of designing the intermediate flow is that when the main spool valve is in the middle position, it can relieve the pressure and prevent the air-conditioning system from being damaged by high pressure.

2. The relationship between pressure difference and flow rate: The basic condition for the reversing of the four-way valve is that the pressure difference at both ends of the piston (that is, the pressure difference between the exhaust pipe and the suction pipe) (F1-F2) must be greater than the frictional resistance f, otherwise, the four The through valve will not reverse direction. The minimum operating pressure difference required for reversing is guaranteed by the system flow. When the pressure difference (F1-F2) between the left and right piston chambers is greater than the frictional resistance f, the four-way valve starts to change direction. When the main slide valve moves to the middle position, the E, S, and C pipes of the four-way valve are connected to each other, compressing Part of the refrigerant discharged from the compressor will flow directly from the four-way valve D through the E and C connections to the S connection (compressor air return port), forming an instantaneous gas flow state.

At this time, if the refrigerant flow rate discharged by the compressor is much greater than the intermediate flow loss of the four-way valve, the high and low pressure difference will not decrease greatly, and the four-way valve has a large enough reversing pressure difference to make the main spool valve in place; if the compressor discharges When the refrigerant flow of the four-way valve is insufficient, the high and low pressure difference will be greatly reduced due to the loss of the intermediate flow of the four-way valve. In the middle position, a string of gas is formed.

Three. Possible reasons for insufficient refrigerant flow

1. External leakage occurs in the air-conditioning system, resulting in insufficient refrigerant circulation in the system;
2. When the weather is very cold, the refrigerant evaporation is not enough;
3. The four-way valve is not well matched with the system, and the selected four-way valve has a large intermediate flow and a small system capacity;
4. Air conditioner reversing time. Generally, the system is designed so that the four-way valve does not change direction until the compressor is stopped for a certain period of time. At this time, the high and low pressure tend to balance, and the reversing stops at the middle position, that is, the four-way valve is not reversed in place, and the main spool valve stops at the middle position. At the next startup, the flow is insufficient due to the effect of the intermediate flow;
5. When the compressor starts, the flow is insufficient, and the inverter is more obvious.

Four, the possible reasons for the poor commutation of the four-way valve

1. The coil is disconnected or the voltage does not meet the coil regulations, causing the spool of the pilot valve to fail;

2. Due to external reasons, the pilot valve part is deformed, causing the valve core to fail to move;

3. Due to external reasons, the capillary tube of the pilot valve is deformed, the flow is insufficient, and the pressure difference required for reversing cannot be formed and cannot be actuated;

4. Due to external reasons, the main valve body is deformed, and the piston part is stuck and cannot move;

5. The debris in the system enters the four-way valve and blocks the piston or the main spool valve and cannot move;

6. When the piping is brazed, the temperature of the main valve body exceeds 120°C, and the internal parts are thermally deformed and cannot move;

7. There is an external leakage of refrigerant in the air-conditioning system, the amount of refrigerant circulation is insufficient, and the pressure difference required for commutation cannot be established and cannot be operated;

8. The refrigerant circulation volume of the compressor cannot meet the necessary flow of the four-way valve reversing;

9. When the speed frequency of the inverter compressor is low, the necessary flow required for commutation cannot be guaranteed;

10. The scroll compressor causes hydraulic shock to the system, causing the piston of the four-way valve to be damaged and unable to operate.

Five, four-way valve string gas judgment

The method of distinguishing the gas flow: touch the lower three pipes of the four-way valve by hand, if all of them are hot, it means that the four-way valve is not in place, and it is in the middle gas flow state. A small piece of magnet can also be used. When the direction is reversed, the small magnet does not move with it, which also means that the gas is trapped. A certain amount of refrigerant is charged into the system, and the direction can be reversed in place.

There are many factors that cause the four-way valve to not change direction. During maintenance, it is often manifested as no cooling or no heating. The elimination methods are as follows:

(1) First check whether the refrigerant in the system is sufficient (it is not comprehensive to judge whether the pressure of the system is sufficient);

(2) Check the system for refrigerant loss caused by external leakage;

(3) Check whether the four-way valve body and capillary tube are damaged or deformed;

(4) Judging whether the coil is turned on and off is normal, and whether the voltage is within the allowable range of use;

(5) Judging whether the pilot valve is active or not, there is a “tower, tower, tower” spool slamming sound when the coil is turned on or off, indicating that the pilot valve operates normally. At this time, it is best to energize only the four-way valve in order to listen to the sound.

(6) The pilot valve acts normally and the main valve body does not act, indicating that the minimum operating pressure difference required for the four-way valve reversing has not been established. Sufficient refrigerant can be charged into the system to make it commutate normally.

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