Expanse on valve setting
If an expansion valve is set for 5K superheat, the temperature at the thermal bulb position would be (-7.5 C 5) D -2.5 °C.
Manufacturers of coolers, units and expansion valves will be pleased to supply capacity ratings for their products upon request.
Klea 407A is suitable for operation at temperatures between -35 °C up to 45 °C with discharge temperatures that compare favourably with R502.
Klea 407B, when used in existing R502 systems within a temperature range of -40 to 40 °C and where discharge temperatures are critical, also compares favourably.
Klea 66 (407C) can be compared generally to R22 with lower discharge temperatures.
Changing the refrigerant charge
The actual task of replacing the refrigerant in an existing plant is not a simple one like replenishing a charge. Various service organizations no doubt have their own procedures. A few manufacturers have adopted the method known as retrofit procedure but this procedure is not common to all replacement refrigerants and it is imperative that the following points should be noted.
1 Check the existing system design and operating pressures to ascertain that they are compatible with the new refrigerant. The manufacturer of the equipment should be consulted if in doubt.
2 Change the compressor lubricating oil to that recommended according to the refrigerant used.
3 Flush the system through with the original refrigerant to reduce the percentage of oil contamination.
4 If necessary change shaft seals, filter driers, components containing elas- tomers and expansion valves to required types.
5 Adjust expansion valve superheat settings for optimum performance.
6 Reset pressure operated safety switches if necessary. If fusible plugs are installed check that the rating is satisfactory for operation with the replace- ment refrigerant.
A refrigeration system charged with a CFC or HCFC will probably use a mineral oil for lubrication. This type of oil may not be suitable for use with the replacement refrigerant. Before commencing any procedure it is advisable to consult the equipment manufacturer to determine suitability of the system components with the replacement refrigerant. It is also most important to determine the performance of the evaporator with a proposed replacement refrigerant.
A polyol-ester (PE) lubricating oil has been introduced which is generally a preferred choice. The PE lubricating oil may be used with some of the new refrigerants but not all of them.
For example, the stability of a system charged with HCFC 134a will possibly be reduced if the system contains chloride ions. HCFC 134a is an acceptable replacement for CFC 12 in a new installation which has not previously operated with a CFC. Before the system is commissioned the type of lubricating oil in the compressor should be checked. HCFC 134a should not be used in a system that has previously operated with CFC 12 until the system has been flushed extensively. Mineral oils normally used with CFC 12 are insoluble in HCFC 134a and a suitable oil must be used.
Replacement refrigerants may act as a solvent to elastomers or other materials used in the construction of shaft seals, filter driers and various types of valves. Gaskets between planed surfaces may also be suspect and once again it must be stressed that advice regarding system components should be sought to avoid unnecessary malfunctions.