The Solutions of Common Low Pressure for Chillers 2019-07-26

There are many factors that cause low-pressure failure of cold water (freezer) machines, and we only list some of them today. It can be roughly divided into the following categories (from easy to difficult sequence) system leakage, system blockage, and evaporator blockage.

Important: The "Reset button" on the pressure controller must be pressed after each fault point has been processed. Common low pressure fault analysis and processing are also applicable to other types of refrigeration units. (The pressure reset button is a small red button on the white plastic box on the left hand side of the control box, the screw type freezer, the pressure controller is located outside the control box, on the left hand side, is a green plastic box)

Fault 1: The system has leaked

There are leak points in the connection pipe of the refrigeration system, such as welding problems, corrosion problems caused by the environment, fractures caused by mechanical vibration, human factors, etc.

Handling: This type of problem is relatively simple to handle. First, use leak detection fluid (soap water, or detergent to water) or halogen leak detector to find the leak point. When the leak point is found, weld it with welding equipment and do it. After the necessary vacuum treatment, the equipment can be resumed after the refrigerant is charged according to the amount specified by the manufacturer.

Fault 2: System blockage

There are four reasons for the blockage of the refrigeration system:

a, blockage of debris;

b, ice block;

c, the solenoid valve is broken;

d, the expansion valve is broken.

1. Blockage of debris:

Because the refrigeration system has strict requirements in all aspects of production and manufacturing, it is necessary to ensure that each link is cleaned. However, most of the cold water (freezing) machine manufacturers are purchasing parts and assembling them. This will inevitably lead to some systems that are not pure. In severe cases, the system will block. (Generally, blockages occur in filters or expansion valves. At the entrance) Therefore, manufacturers of cold water (freezer) machines have installed "filters" in the refrigeration system to filter out impurities in the system. When the impurities in the piping of the refrigeration system accumulate to a certain extent, the filter will be clogged, affecting the throughput of the refrigerant in the system, and a low-voltage fault will occur in severe cases.

Identification: If the filter is clogged due to dirty system, it will only cause the cooling capacity of the device to drop, or even you will not be affected. When the "filter" is slightly blocked, there is a temperature difference between the inlet and outlet of the "filter", and the inlet and outlet can be felt by hand. In severe cases, condensation or frosting may occur in the filter. If condensation or frosting of the filter is encountered (the condensation does not occur when the machine is running, the condensation is not counted).

Handling: Replace the filter of the same model.

2. ice block:

Ice blockage is essentially the presence of moisture in the system piping. The moisture in the system runs with the refrigerant to the throttle valve (expansion valve) after throttling expansion, forming a low temperature and low pressure at the outlet of the throttle valve, when the evaporation temperature (section) When the outlet temperature of the flow valve is below the freezing point, the moisture in the refrigerant will form ice cubes here, which blocks the throttle valve (expansion valve) from forming a low pressure fault. The ice block occurs at the outlet of the throttle valve (expansion valve).

Disposal: First use a detachable filter with “calcium chloride” (a strong water-absorbing material) to thoroughly filter the moisture in the system and replace it with a disposable filter of the same model. .

3. Solenoid valve:

Solenoid valve is an indispensable accessory in the refrigeration system. It has the function of protecting the safety of the system. (When the compressor stops working, the refrigerant is cut off, and the refrigerant is not allowed to continue to flow to the evaporator. If the compressor has a large amount of refrigerant in the evaporator, When the compressor is started again next time, it is easy to cause the compressor valve to catch liquid and damage the compressor). When the solenoid valve is damaged, the circulation of the refrigerant is blocked, resulting in a low voltage failure. At present, most manufacturers have omitted the solenoid valve in order to reduce the cost, but this also left a hidden danger to the equipment.

Identification: Solenoid valve is better judged, and the solenoid valve is broken in two cases:

1.The solenoid valve coil is burnt and the hair film cannot be opened. The solenoid valve coil can be measured by a multimeter to determine whether the solenoid valve is burnt;

2.The solenoid valve body itself is broken, causing the membrane inside the valve to not open. When there is a temperature difference between the inlet and outlet of the solenoid valve, it indicates that the solenoid valve is defective.

4.Damage to the expansion valve:

The expansion valve is one of the four major components of the refrigeration system and is an indispensable component. After the condensed low-temperature high-pressure refrigerant flows through the expansion valve, it is throttled by the expansion valve, and expands and evaporates at the outlet of the expansion valve to form a low-temperature and low-pressure gas-liquid mixed refrigerant, thereby taking away heat in the system to form a refrigeration process.

The expansion valve has a mechanical expansion valve and an electronic expansion valve. Mechanical expansion valves are affected by the environment during use. Some environments have corrosive gases that corrode liquids, causing the expansion valves to corrode. Most of them are gas leaks in the temperature sensing package of the expansion valve (corrosion of the connecting tube connecting the temperature sensing package and the valve body) ). Although the electronic expansion valve has the advantages of large temperature control range and high precision that the mechanical expansion valve cannot exceed, it has an independent control system, which also increases the failure rate invisibly.

Handling: In case of expansion valve damage, only replacement.

Fault 3: The heat exchange capacity of the evaporator is seriously insufficient

There are two reasons for the insufficient heat exchange of the evaporator: a, insufficient water flow in the evaporator, b, foreign matter blockage in the evaporator (or fouling on the surface of the evaporator tube in the evaporator, or insufficient heat generation due to crystallization)

1. Insufficient water flow in the evaporator:

The main factors causing this phenomenon are water pump failure or foreign matter entering the pump impeller, or air leakage in the water inlet pipe (more difficult to check, need to be carefully analyzed) to cause insufficient water flow.

Disposal: Replace the pump, or disassemble the pump to clear the foreign matter in the impeller to eliminate the fault.

2. The evaporator is blocked or fouled:

To determine if the evaporator is clogged or the evaporation tube is fouling, first remove the pump problem and make sure that the pump and inlet lines are normal. The evaporator blockage or structure has a common and very obvious feature (only for medium temperature units): when the equipment is normal, the compressor surface will not have a large amount of condensed water or frost or ice. When you see a large amount of condensed water or frost and ice on the surface of the compressor, it can be basically determined that the evaporator is clogged.

Disposal: If the evaporator is clogged or the evaporation tube is fouled, the evaporator should be disassembled, and the evaporation tube should be discharged with a high-pressure water gun or soaked with a special liquid.

Note: Some evaporators are chemical liquids, such as the refrigerator of aluminum oxidation (anodizing) processing plant. The vaporizer contains the sulfuric acid solution. When certain conditions are met, the sulfuric acid will crystallize and block. The evaporator, if it is a pure sulfuric acid crystal blockage, can be dissolved by circulating it in the evaporator with hot water above 50 degrees. Others are used in electroplating plants, such as acid galvanizing. Some acid galvanizing liquids contain “potassium chloride”. When the liquid containing “potassium chloride” passes through the surface of the evaporator tube of the evaporator, the surface temperature of the evaporation tube is very low (less than the saturation temperature), which may result in “ Potassium chloride "precipitates crystals. After the accumulation of these crystals, the evaporation tube is covered with a thick layer of "potassium chloride" clothes, which causes the evaporator to lose heat exchange capacity. Slightness is manifested by a decrease in cooling capacity and a low-voltage failure in severe cases. (This is the case when the purchase is not correct)

Some of these problems can be handled by customers themselves. When it comes to professional knowledge, you still need to ask professionals to deal with them. Do not blindly repair, so as not to cause unnecessary economic losses.

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