Fault determination of four-way valve reversal (air blow) in air conditioning system

Among the four-way valves returned in the air-conditioning market, the vast majority are marked with poor reversal or gas leakage. Performance tests are carried out on these returned products, except that when the four-way valve is removed, the piston and main slide valve are burnt out and accidents Except for the bruise and deformation that cannot be analyzed, the rest meet the performance specifications of the four-way valve, and the direction change is normal. Therefore, there is a certain misjudgment phenomenon, and this misjudgment has caused considerable quality loss to the business unit. The following air-conditioning maintenance will start with the operation principle and structural characteristics of the four-way valve, analyze the causes of poor reversing (air leakage) in the market and the correct judgment method, in order to help air-conditioning after-sales service.

The structural characteristics of a four-way valve

1 Intermediate flow

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

2 The relationship between pressure difference and flow

The basic condition for the reversing of the four-way valve is that the pressure difference between the two 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-way valve will not change direction. The lower operating pressure difference required for reversing is ensured by the system flow rate (as shown in the figure above). When the pressure difference between the left and right piston chambers (F1-F2) is greater than the frictional resistance f, the four-way valve starts to change direction. When the main spool valve moves to the middle position, the three-way valve E, S, and C are connected to each other, compressing A part of the refrigerant discharged from the machine will flow from the four-way valve D to the S port (compressor return port) directly through the E and C ports, 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 drop greatly. The four-way valve has a large enough reversing pressure difference to make the main slide valve in place; if the compressor is discharged When the refrigerant flow is insufficient, the high and low pressure difference will be greatly reduced due to the intermediate flow loss of the four-way valve. When the high and low pressure difference is less than the lower operating pressure difference required for the four-way valve to switch, the main valve will stop. In the middle position, a string of gas is formed.

Two Shanghai Decoration Design Company tells you the possible causes of insufficient refrigerant flow

1 External leakage of the air-conditioning system causes insufficient refrigerant circulation in the system;

2 When the weather is very cold, the amount of refrigerant evaporation is not enough;、

3 The four-way valve is not well matched with the system, that is, the selected four-way valve has a large intermediate flow rate and low system capacity;

4 Air conditioner reversing time. The general system design is that the four-way valve changes direction after the compressor stops for a certain period of time. At this time, the high and low pressure tends to balance, and it stops when the direction changes to the middle position. That is, the four-way valve does not change direction and the main slide valve stops at the middle position. The next time it is started, 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.