Eliminate the "Blockage" Faults (Ice Blockage, Dirt Blockage, Oil Blockage) of the Refrigeration System in 5 Minutes

I. Three Types of "Blockage" Faults in the Refrigeration System:
Regarding the blockage of the refrigeration system, it can usually be divided into three major categories: ice blockage, dirt blockage (also known as contamination blockage), and oil blockage. Among them, dirt blockage and oil blockage are further divided into two types: complete blockage and slight blockage.
II. Analysis of the Causes of Blockage in the Refrigeration System:
Causes of Blockage:
Ice Blockage: Due to the moisture in the system exceeding the allowable value;
Dirt Blockage: Excessive impurities, such as the residual dirt in the system during the manufacturing of refrigeration equipment, the shedding of metal oxides in the pipeline, the powder of molecular sieves or silica gel, and the dirt accidentally entering during the maintenance process, etc., block the pipeline or the pipeline is deformed under pressure (severe blockage);
Oil Blockage: Excessive charging of refrigeration oil and the deterioration and accumulation of the oil in the bends of the pipeline, at the places with a smaller pipe diameter, or the refrigeration oil becoming viscous when cooled at the capillary tube, or the excessive adhesion of the refrigeration oil on the inner wall of the pipeline due to long-term use (oil blockage) cause the blockage of the system.
III. Fault Phenomena and Identification of Blockage Categories:
Common Characteristics: The condenser is not hot or not hot enough, the evaporator does not frost or only partially frosts, there is no airflow sound of the refrigerant flowing or the sound is very low, the low-pressure is on the low side or in a negative pressure state, while the high-pressure is on the high side (this is the difference from the situation of insufficient refrigerant); the working current is smaller than the normal value.
Individual Characteristics:
A. Ice Blockage: The phenomenon of "intermittent and repeated refrigeration or periodic non-refrigeration" occurs.
B. Dirt Blockage, Severe Blockage, Oil Blockage: Different from ice blockage, there will be no phenomenon of "intermittent and repeated refrigeration". Once blocked, the system cannot refrigerate or the refrigeration effect is poor.
Method to Determine Whether It is Dirt Blockage or Oil Blockage: In the system with capillary tube throttling, cut off the capillary tube at a position 0.5cm away from the drier-filter.
01. If there is no refrigerant ejected, cut open the other end of the drier-filter. If there is still no refrigerant ejected, it means that the refrigerant has completely leaked;
02. If there is a large amount of refrigeration oil mixed in the refrigerant ejected after cutting the capillary tube, it means that there is an oil blockage at the capillary tube.

03. If the refrigerant is ejected and there is not much oil, it can be determined that there is a dirt blockage fault at the capillary tube.
In the system with expansion valve throttling, first recover the refrigerant, then remove the filter screen at the inlet of the expansion valve and the solenoid valve, clean them with gasoline, dry them, and reinstall them. At the same time, replace the drier-filter. If the unit operates normally after the test, it is a dirt blockage; if it is still blocked, it is an oil blockage or a severe blockage.
The location of the oil blockage is generally at the sunken part of the bent pipeline and the pipeline under low temperature and low pressure (such as the evaporator and other parts). The location of the severe blockage is generally at the filter, solenoid valve, capillary tube, expansion valve, and the dead bends and deformed parts of the pipeline under pressure. Generally, there will be a frosting or condensation phenomenon at the blocked location.
C. Slight Blockage: It takes a long time for the evaporator to be fully frosted or it cannot be fully frosted. The condenser, drier-filter, and compressor are warmer than the normal temperature, the working current is larger, and the system can refrigerate, but the effect is poor.
Distinguishing Characteristics of Different Blockages:
01. The Specific Characteristics of Drier-filter Blockage: Condensation or frosting occurs at the capillary tube. This is because the filter plays a throttling role, and the capillary tube is equivalent to an evaporator - it absorbs heat and condenses.

02. The Important Distinguishing Characteristics between the Presence of Air in the Refrigerant and Excessive Refrigerant:
a. The upper part of the high-pressure pipe and the condenser is very hot to the touch, while the lower part is obviously not hot.
b. Ice beads sometimes appear at the outlet of the capillary tube.
c. The evaporator shows periodic frosting.

d. When the refrigeration system is operating, the pointer of the high-pressure gauge connected to the high-pressure side swings left and right with a slightly large amplitude and is unstable; at the same time, the pointer of the pressure gauge swings quickly, and the swing is in the same frequency as the movement of the piston.
e. The vibration of the outdoor unit is larger than that of a normal unit because air is incompressible. If there are the above symptoms, it can be determined that there is air in the system.
IV. Elimination Methods
(1) Ice Blockage:
A. Heating and Evacuation Method (also known as Exhaust Baking Method):
While evacuating the system, heat up components such as the compressor, condenser, drier-filter, and evaporator. It is best to use a vacuum pump with a flow rate of 2 to 4L/second for evacuation, which can achieve a better evacuation effect. The evacuation time is generally about 4 hours.
B. Fluorine-nitrogen Flushing Method (also known as Fluorine-nitrogen Dehydration Method):
After evacuating the system, charge the system with a certain pressure of refrigerant or dry nitrogen, then start the compressor for 5 to 10 minutes, and then release the fluorine or nitrogen that has absorbed part of the moisture in the system. Repeat this process two or three times to remove the moisture.
C. Water Absorption Method with a Second Drier-filter:
In the connection between the conventional drier-filter and the capillary tube, weld open and pull out the liquid outlet end of the capillary tube at the inlet end of the evaporator, then insert it into the inlet end of another added drier-filter and weld it well. Then, weld the outlet end of the drier-filter to the inlet end of the evaporator.
This method has a better water absorption effect than the conventional single drier-filter and can completely eliminate the ice blockage fault. However, it may have a slight impact on the pressure of the low-pressure side of the original system, so it can only be used when it is necessary for a major overhaul or the replacement of an internally leaking evaporator. If the pressure of the low-pressure side decreases due to the addition of the drier-filter, which affects the refrigeration effect, the length of the capillary tube can be appropriately shortened to eliminate the impact.
(2) Dirt Blockage:
Dirt blockage mostly occurs at the capillary tube (or expansion valve), drier-filter, liquid outlet valve, and other parts. The drier-filter should be replaced after it is blocked. The expansion valve can be disassembled and cleaned if it is blocked. When it is inconvenient to replace the capillary tube, nitrogen with a pressure of about 1MPa can be used for flushing. The nitrogen should be flushed in the opposite direction of the refrigerant flow (that is, enter from the return air pipe end and then be released from the outlet of the condenser or from the capillary tube. During the flushing process, press and release the exhaust port with your hand to increase the impact force on the capillary tube.
(3) Oil Blockage:
First, weld open the pipeline, bake each welding point with a neutral flame, and pull out the welding joints of the low-pressure suction pipe, the process pipe, and the drier-filter after melting them. Then start the compressor, and use a low-temperature flame to bake the high-pressure exhaust pipe and the condenser (starting from the end connected to the compressor). Use the high-pressure gas discharged by the compressor to discharge the refrigeration oil vaporized by baking until all the residual oil in the condenser is removed. For the oil blockage of the evaporator, the evaporator can be removed together with the low-pressure pipe and the capillary tube. Then connect the low-pressure pipe to the nitrogen cylinder, and flush and bake the low-pressure pipe, the evaporator, and the capillary tube with pressurized nitrogen to wash away the residual oil.
If the evaporator cannot be removed, the low-pressure pipe at the end close to the compressor can also be welded off. Start the compressor and block the low-pressure pipe orifice with your hand at the same time. When you feel that you can't block it anymore, suddenly remove your hand to let the oil be discharged together with the gas. Repeat this spraying process several times.