Refrigeration System Failures: Handling System Blockages and Water Infiltration

2024-12-27

I. Three Types of "Blockage" Faults in Refrigeration Systems

Regarding the blockage of refrigeration systems, it can usually be divided into three major categories: ice blockage, dirt blockage (also known as fouling blockage), and oil blockage. Among them, dirt blockage and oil blockage can be further divided into two types: complete blockage and slight blockage.

Analysis of the Causes of Refrigeration System Blockage

Causes of Blockage:

Ice Blockage: Due to the moisture in the system exceeding the allowable value.
Dirt Blockage: Excessive impurities, such as residual dirt in the system during the manufacturing of refrigeration equipment, detachment of metal oxides in the pipeline, molecular sieve or silica gel powder, and dirt accidentally entering during the maintenance process, etc., which block the pipeline or cause the pipeline to be deformed under pressure (bad blockage).
Oil Blockage: Excessive filling and deterioration of refrigeration oil accumulate in the bends of the pipeline, where the pipe diameter is small, or the refrigeration oil becomes viscous when cooled at the capillary tube, or too much refrigeration oil adheres to the inner wall of the pipeline due to long-term use (oil blockage), resulting in system blockage.

Identification of Fault Phenomena and Blockage Categories

Common Characteristics: The condenser is not hot or not hot enough, the evaporator does not frost or only frosts partially, there is no sound of refrigerant flowing or the sound is small, the low-pressure pressure is low or in a negative pressure state, while the high-pressure is high (this is the difference from insufficient refrigerant); the working current is smaller than the normal value.
Individual Characteristics:

A. Ice Blockage: The phenomenon of "intermittent and repetitive refrigeration or periodic non-refrigeration" occurs.
B. Dirt Blockage, Bad Blockage, Oil Blockage: Different from ice blockage, there will be no "intermittent and repetitive refrigeration" phenomenon. Once blocked, it cannot refrigerate or the refrigeration effect is poor.

Methods for Judging Dirt Blockage and Oil Blockage

In a system using capillary tube throttling, cut off the capillary tube at a position 0.5 cm close to the drying filter.

01. If no refrigerant is ejected, cut open the other end of the drying filter. If there is still no refrigerant ejected, it means that the refrigerant has leaked completely.
1. If there is a large amount of refrigeration oil mixed in the refrigerant ejected after the capillary tube is cut, it indicates oil blockage at the capillary tube.
1. If refrigerant is ejected and there is not much oil, it can be determined that a dirt blockage fault occurs at the capillary tube.

In a system using an expansion valve for throttling, first recover the refrigerant, then remove the filter screen and solenoid valve at the inlet of the expansion valve, clean them with gasoline and dry them before reinstalling. At the same time, replace the drying filter. If the test run is normal, it is dirt blockage; if it is still blocked, it is oil blockage or bad blockage.

The location of oil blockage is generally at the sagging part of the pipeline bend and the low-temperature and low-pressure pipeline (such as the evaporator, etc.). The location of bad blockage is generally at the filter, solenoid valve, capillary tube, expansion valve, and the dead bend and deformed part of the pipeline under pressure. Generally, there will be frosting or dew condensation at the blocked part.

C. Slight Blockage: It takes a long time for the evaporator to be fully frosted or it cannot be fully frosted. The condenser, drying filter, and compressor are at a higher temperature than normal, the working current is relatively large, and it can refrigerate, but the effect is poor.

Distinguishing Characteristics of Different Blockages

1. The unique characteristic of drying filter blockage: Condensation or frosting occurs on the capillary tube. This is because the filter plays a throttling role, and the capillary tube is equivalent to an evaporator - absorbing heat and causing condensation.
1. The important distinguishing characteristics between excessive refrigerant and refrigerant with air:
- a. The upper part of the high-pressure pipe and the condenser is extremely hot, while the lower part is obviously not hot.
- b. Ice beads sometimes appear at the outlet of the capillary tube.
- c. The evaporator has periodic frosting.
- d. When the refrigeration system is running, the pointer of the high-pressure gauge connected to the high-pressure side swings slightly larger and is unstable; at the same time, the pointer of the pressure gauge swings faster, and the swing frequency is the same as that of the piston movement.
- e. The outdoor unit vibrates more than the normal unit because air is incompressible. If the above symptoms occur, it can be judged that there is air in the system.

Exclusion Methods

(1) Ice Blockage:
- A. Heating and Evacuation Method (also known as Exhaust Baking Method):
  While evacuating the system, heat and raise the temperature of components such as the compressor, condenser, drying filter, and evaporator. It is best to use a vacuum pump with a flow rate of 2 - 4L/s for evacuation, so that the evacuation effect is better. The evacuation time is generally about 4 hours.
- B. Fluorine-Nitrogen Gas Flushing Method (also known as Fluorine-Nitrogen Gas Dehydration Method):
  After evacuating the system, charge the system with a certain pressure of refrigerant or dry nitrogen, then start the compressor for 5 - 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. Secondary Drying Filter Water Absorption Method:
  In the connection between the conventional drying filter and the capillary tube, weld and pull out the liquid outlet end of the capillary tube and the inlet end of the evaporator, then insert it into the inlet end of another added drying filter and weld it well, and then weld the outlet end of the drying filter to the inlet end of the evaporator.
  This has a better water absorption effect than a conventional single drying filter and can completely eliminate ice blockage faults. However, it may slightly affect the pressure on the low-pressure side of the original system. Therefore, it can only be adopted when overhauling or replacing an evaporator with internal leakage. If the pressure on the low-pressure side decreases due to the addition of a drying filter, affecting the refrigeration effect, the length of the capillary tube can be appropriately shortened to eliminate the impact.
(2) Dirt Blockage:
Dirt blockage mostly occurs in components such as the capillary tube (or expansion valve), drying filter, and liquid outlet valve. The drying filter should be replaced after being blocked. The expansion valve can be disassembled and cleaned if it is blocked. If it is inconvenient to replace the capillary tube, it can be flushed with nitrogen gas at a pressure of about 1MPa. The nitrogen gas should be flushed from the opposite direction of the refrigerant flow (that is, enter from the return pipe end, and then be discharged from the condenser outlet or the capillary tube. During the flushing process, cover the exhaust port with your hand, release and block it from time to time to increase the impact force on the capillary tube.
(3) Oil Blockage:
First, weld open the pipeline and bake each welding joint with a neutral flame. Melt and pull out the welding joints of the low-pressure suction pipe, the process pipe, and the drying filter respectively. Then start the compressor, and then bake the high-pressure exhaust pipe and the condenser with a low-temperature flame (starting from the end connected to the compressor) to use the high-pressure gas discharged by the compressor to discharge the vaporized refrigeration oil until all the remaining oil in the condenser is removed. For the oil blockage of the evaporator, the evaporator can be removed together with the low-pressure side and the capillary tube, and then the low-pressure pipe is connected to the nitrogen cylinder. Use pressurized nitrogen to flush while baking the low-pressure pipe, the evaporator, and the capillary tube to clean the remaining oil.
If the evaporator cannot be removed, the low-pressure pipe near the compressor end can also be welded off, the compressor is started, and at the same time, the low-pressure pipe opening is blocked by hand. When it feels that it cannot be blocked, suddenly release the hand to allow the oil to be discharged together with the gas. Repeat this injection several times.

II. Practical Maintenance Cases of Refrigeration System Water Ingress

Let's first look at how to handle a small amount of water in a practical refrigeration system.

Refrigeration System Failures: Handling System Blockages and Water Infiltration1735308558078

Refrigeration System Failures: Handling System Blockages and Water Infiltration1735308558069

First of all, if the water content is incorrect, it is not necessary to completely release all the refrigerant in the system, as this will greatly increase the maintenance cost. At this time, we only need to add a drying filter in the system (the liquid pipe after the condenser or the low-pressure side: the reason is that we can recover the refrigerant to the condenser, so that when modifying the system, it is not necessary to release all the refrigerant in the system). Absorb the water in the system through the drying filter. The following is a picture of a practical maintenance case:

Materials and Tools Required for Modification

Color-Changing Silica Gel:
Color-changing silica gel will change color when it encounters water.
Detachable Drying Filter:
Add the drying filter to the refrigeration system according to the following steps:
After completion, start the machine and run it. The frequency of replacing the color-changing silica gel in the early stage can be more frequent, for example, replace it once every 1 - 2 hours. After the water in the refrigeration system is basically absorbed, the unit can be allowed to run normally for several days, and then come back to replace the color-changing silica gel. If it is found that the silica gel has not changed color, it indicates that the water in the refrigeration system has been completely absorbed.