How to repair r134a refrigerator refrigerant?

The refrigerant HFC-134a, namely tetrachloroethane, belongs to halogenated hydrocarbons, but does not contain fluorine and bromine, so the ozone depletion potential is zero. The main refrigerants currently used in household refrigerators are R12 (CFC-12), R134 (HFC-134a), HC-600a, etc. The application technology of replacing R12 with HFC-134a refrigerant is becoming more and more mature. The cabinet structure, main components, refrigeration system, and electrical system of this type of refrigerator are basically the same, so the common fault characteristics and maintenance technology have many similarities or similarities, but there are also some differences, mainly caused by the characteristics of the refrigerant The related materials and maintenance methods are different. The following introduces some of the problems that should be paid attention to when repairing this type of refrigerator.

1. HFC-134a compressor

Compared with CFC-12 compressor, HFC-134a compressor needs to increase by 10 ~15% of the cylinder volume to ensure the same cooling capacity. The condensing pressure is higher and the pressure ratio is greater. In order to obtain the same cooling capacity, some changes were made to the structure and materials of the compressor. The more efficient motor is used to adapt to the harsher system working environment. Other parts and CFC-12 can be used in common, but the content of moisture and impurities is strict **, and the cleanliness requirements are higher. In use, the noise of HFC-134a compressor is slightly larger than that of CFC-12 compressor.

2. Refrigeration oil

Since HFC-134a is insoluble in traditional mineral oil and alkylbenzene oil, new ester lubricants are required. Grease lubricants have extremely strong water absorption. The highly hydrolyzable lipid oil reacts with water to form acid, which will corrode the refrigeration tube and even the compressor. The acid and the lipid oil will decompose and deteriorate, forming a vicious circle. Compressor refrigerating oil must be compatible with the refrigerant, and have good lubricity, airtightness, low temperature fluidity and chemical stability. Since HFC-134a compressors generally use fats or polyglycol (PAG) oils with better compatibility with them, they are different from the mineral oils used in CFC-12 compressors and cannot be replaced with each other, otherwise they will not only not meet the lubrication of the compressor. It is required, and it may freeze and block the refrigeration system. Do not mix them. When repairing and evacuation, the vacuum pump must be replaced with a lipid-based refrigerating oil vacuum pump. If an old vacuum pump is used or a scrapped CFC-12 refrigerator compressor is used to repair and reform the evacuation equipment (refrigerating oil is mineral oil), it must be thoroughly cleaned with lipid oil , And replaced with grease oil, and at the same time replace the connecting hoses, joints and sealing rings. The HFC-134a refrigerant does not contain chlorine atoms, and the halogen leak detector should be changed to an electronic leak detector during leak detection. If you use soapy water to detect low pressure, it should be done after the shutdown pressure is balanced. When cleaning the pipes of the refrigeration system, they should be cleaned with non-chlorine cleaners.

3. Dry filter

Practice has proved that the corrosion caused by moisture is more serious than the hazard of ice blockage. Therefore, HFC-134a refrigerators have very high requirements for the water content control of the refrigeration system. In addition to the strict drying and dehydration with special processes during manufacture, the refrigeration system is equipped with dryers and filters, and molecular sieves are used to absorb the remaining residual moisture. The filter drier consists of two parts: a dryer and a filter: one is to filter out debris and dust in the refrigeration system. In order to prevent clogging of the capillary tube and damage to the compressor; the second is to absorb the residual moisture in the refrigeration system to prevent ice blockage and avoid the corrosion of the refrigeration system by the formation of acids. The filter drier is generally installed in the liquid pipeline between the condenser outlet and the capillary inlet. For the CFC-12 system, choosing 4A molecular sieve, namely XH-5 type, can absorb water well. For the HFC-134a system, an XH-7 (maximum diameter of 3A) dry filter with strong water absorption, a slightly larger volume, and a molecular diameter between HFC-134a and water is required. Due to the different materials used for the two, the weights are also different (XH-5 type generally puts molecular sieve 5g, XH-7 type generally puts 10g), and they cannot be substituted for each other during maintenance.

4. Maintenance operation time

The moisture control of the refrigeration system is a very important and complex task, which can neither be visually inspected nor simple methods. The measurement can only be carried out in accordance with the strictest operating procedures, and special attention should be paid to HFC-134a refrigerators that require high water content control in the refrigeration system. The analysis method of hearing and hand touch can be used for maintenance. Once it is determined that the drying filter is blocked or the compressor is faulty, after opening the refrigeration system, the disconnected pipe orifice should be sealed in time to make the break and weld quickly. It is required that the exposure time of all pipeline components should be as short as possible (about 15 minutes) when repairing, and the filter drier and small pipe fittings should be assembled as soon as possible when unpacking. The evacuation time of HFC-134a refrigerator refrigeration system is longer than that of CFC-12 to ensure that the vacuum degree is less than 60Pa. In maintenance practice, the method of secondary evacuation is often used: the first evacuation is 5 minutes, and 10g of HFC-134a refrigerant is charged; the second evacuation is 20 minutes. This can shorten the vacuuming time, and the effect is better. When brazing the HFC-134a refrigerator refrigeration system, use dry flux as much as possible. If dry flux is not available, copper, silver electrode or low-silver electrode welding materials can also be used instead of flux.

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