Servicing of refrigeration systems. Substitution of R12 for R401A, R409A, R401B. Substitution of R500 for R401B.

• Substitution of R12 for R134a
• Substitution of R502 for R404A or R507
• Substitution of R12 for R401A, R409A, R401B. Substitution of R500 for R401B.
• Substitution of R502 for R402A, R408A, R402B
• Substitution of R22 for R407C

Determination of working parameters of the operating refrigeration system. They put down operation parameters of the system while it is operating on the initial refrigerant (R12 or R500). They determine temperatures and pressures in the evaporator, on suction and charging of the compressor, the level of overheating and aftercooling, etc.

Removal of R12 (or R500) refrigerant out of the refrigeration system and its utilization. R12 (R500) refrigerant is poured out into the ballon with the help of a device ensuring exhaustion till residual pressure (vacuum) 30...35 кPа. If mass of the refrigerant which is recommended to charge into the system is unknown, the poured refrigerant is weighed. After weighing data, it is possible to determine mass of the alternative refrigerant which will be initially charged into the system.

Drainage of mineral oil out of the system and measuring of its quantity. If there was used mineral oil in the system, it is necessary to be drained off. Single procedure of the oil substitution ensures removal of sufficient quantity of the oil out of the system. As it has been already said, in the systems with small hermetic compressors where there is no opening for drainage of the oil, there can be necessary to disassemble the compressor. In this case the oil is drained through the compressor suction line and it makes it possible to remove the most of the oil quantity. In bigger systems there can occur necessity of additional drainage out of the other points of the system, in particular, out of the low zones of the evaporator; in this case it is possible to drain off 50...80 % of the oil. If the system contains the oil eliminator, then all the oil contained there is drained off.

In any case they measure the quantity of the oil drained off the system and they compare the obtained result with passport data of the compressor in order to make sure that the main part of the oil has been drained off. If during start there will be observed low operational efficiency of the system, then there can be required repeated substitution of the oil. Experience of "Du Pont" company shows that the number of such cases constitutes less than 1 % of the total quantity of performed substitutions.

Substitution of mineral oil for alkylbenzene in the refrigeration system. The system is filled with alkylbenzene (or polyester) oil whose volume should be equal to the volume of the oil drained off while performing previous operation. At that, they use the oil with such viscosity and of such quality, which are recommended by the factory - manufacturer of the compressor for the alternative refrigerant. If such information about the compressor is not available, viscosity of the new compressor should be close to viscosity of the drained mineral oil. For the majority of compressors, typical viscosity corresponds to standards of 150 SUS or ISO 32.

Operations of drainage and substitution of the oil should be missed, if the system has been already charged with alkylbenzene oil or when mineral oil is not substituted.

Substitution of the filter-dehydrator. This operation is a simple procedure which is performed during technical maintenance of the system. For substitution they use adsorbents compatible with refrigerants R401A, R409A and R401B.

Vacuumization of the refrigeration system and checking of its hermiticity. During vacuumization there are used standard methods of technical maintenance. In order to eliminate the air and other permanent gases out of the system, it should be exhausted till vacuum (66,5 Pа).

Charging of the refrigeration system with the refrigerant. Liquid should be poured out only of the ballon. Ballons with refrigerants are provided with immersion legs , with the help of which it is possible to drain off the liquid out of the ballon being in vertical position. Proper position of the ballon during drainage of the liquid is shown by arrows on the ballon and on the box for the ballon. Refrigerant can be charged into the system either in the state of liquid in the gaseous state depending on what is required. If it is necessary, during transfer of the liquid into gaseous state there should be used valves of collecting pressure gages or throttling device.

Usually for charging of the refrigeration system there is required smaller mass of the alternative refrigerant compared to the mass of R12. Optimal mass of the portion, which, as it has been stated, depends on the system structure and conditions of its operation, constitutes for R401A R401B and R409A 75...90 % of the mass of initial charging with refrigerant R12. During substitution of R500 for R401B, for charging of the refrigeration system there is required a bit larger portion constituting approximately 105 % of mass of the initial refrigerant R500, charged into the system.

In order to obtain optimal results, it is recommended to charge the system initially with the refrigerant in the quantity constituting 75 % of mass of the initial refrigerant. While substituting R500 for R401B it is necessary to start from the portion of 100 % of mass of the initial refrigerant (R500).

During initial charging, the refrigerant should be delivered to the line of the system high pressure (compressor is not working) until pressure in the system has not become equal to the pressure in the ballon. After that the line of the system low pressure is connected, compressor is started and residue portion of the liquid refrigerant is slowly drained off the ballon. After having drained off the liquid out of the ballon, it is necessary to perform charging slowly in order to make it possible for the refrigerant to pass into the gaseous state (vaporize) before it has entered the compressor suction line, and thus, to avoid the compressor collapse.

Start of the refrigeration system and regulating of the charging dose. The system is started and working mode is waited for to be stabilized. If the system is undercharged, the refrigerant should be added in small portions (while continuing to drain the liquid out of the filing ballon) until working parameters have not reached desired values. When comparing pressures and temperatures, it is necessary to use tables.

In the table there is included the line where there is given average temperature of the phase transfer in the evaporator (condenser). Working characteristics of the evaporator (condenser) will be as if it is operating at this permanent temperature and corresponding pressure. This average temperature can be used for comparison of refrigerants.

HCFC refrigerants (R401A, R401B and R409A) are more sensitive to the quantity of the substance charged into the system than CFC refrigerants. At overcharging or undercharging, characteristics of the system operation are changing quickly. Control of the system operation can be realized after the quantity of the refrigerant charged into the system.

After substitution of R12 refrigerant for R401A, R409A, R401B, operation parameters of the refrigerating system can have the following values (see the table).

Experience of operation with R401A, R409A and R401B shows that in the systems charged with one of these refrigerants, there can be successfully used mineral oil in those cases when oil return from the evaporator into the compressor is not vitally important. To such systems there are referred, for example, chamber refrigerators, refrigeration windows, commercial refrigeration automatic machines and domestic refrigerators. However, in the systems with poor oil return, substitution of mineral oil for synthetic oil can occur necessary, especially if the evaporator is remote from the compressor or is situated lower than the compressor or there are areas in the system with low speed of the refrigerant movement.