Service blends as substitutes for R12 (R500)
Although (as experience already shows) R134a is also well suited for the conversion of existing R12 plants, the general use for such a "retrofit" procedure is not always possible. Not all compressors which have previously been installed are designed for the application with R134a. In addition, a conversion to R134a requires the possibility to change the oil, which is for example not the case with most hermetic compressors.
Economic considerations also arise, especially with older systems, where the effort of converting to R134a is relatively high. The chemical stability of such systems is also often insufficient and thus the chance of success is very questionable.
Therefore "Service blends" are also available for such systems as an alternative to R134a and are offered under the designations R401A/R401B*, R409A*. The main components are the HCFC refrigerants R22, R124 and/or R142b. Either HFC R152a or R600a (Isobutane) is used as further component. Operation with traditional lubricants (preferably semi or completely synthetic) is also possible due to the major proportion of HCFC.
A further service blend was offered under the designation R413A (ISCEON® 49 – DuPont), but replaced by R437A by the end of 2008. However, because of the development history of service blends, R413A will continue to be covered in this Report. The constituents of R413A consist of the chlorine free substances R134a, R218, and R600a. In spite of the high R134a content, the use of conventional lubricants is possible because of the relatively low polarity of R218 and the favourable solubility of R600a.
R437A is a blend of R125, R134a, R600 and R601 with similar performance and properties as R413A. This refrigerant is also chlorine-free (ODP = 0).
However, due to the limited miscibility of R413A and R437A with mineral and alkylbenzene oils, oil migration may result in systems with a high oil circulation rate and/or a large liquid volume in the receiver – for example if no oil separator is installed.
If insufficient oil return to the compressor is observed, the refrigerant manufacturer recommends replacing part of the original oil charge with ester oil. But from the compressor manufacturer's view, such a measure requires a very careful examination of the lubrication conditions. For example, if increased foam formation in the compressor crankcase is observed, a complete change to ester oil will be necessary. Moreover, under the influence of the highly polarized blend of ester oil and HFC, the admixture of or conversion to ester oil leads to increased dissolving of decomposition products and dirt in the pipework. Therefore, generously dimensioned suction clean-up filters must be provided. For further details, see the refrigerant manufacturer's "Guidelines".
* By using R22 containing blends, the legal requirements are to be followed (R22 as transitional refrigerant).