Technicians must be up to date with refrigerants before using them to ensure the efficiency of the unit and to limit callbacks.

Superheat is a term that everyone in the hvacr industry should be familiar with. Basically, it is the absorption of sensible heat to the refrigerant in the evaporator inlet and the evaporator outlet. A proper superheat reading gives the technician much-needed information, such as the level of refrigerant in the system, and it guarantees no liquid slugging of the compressor. Since forever, technicians have been taught that on an expansion valve system, the superheat should be between 8° and 12°F — but not anymore. Caution must be taken when reading superheat.

Here is the issue with superheat and new refrigerants: It is possible to slug the compressor with an 8° to 12° superheat when using HP80. If you are using MP-39, the superheat should be between 5° and 9°. As you can see, technicians may create problems instead of repairing them if they do not become familiar with the properties of new refrigerants.

Manifold gage pressure and capacity will also be affected by a conversion of refrigerant. In the “old days,” technicians took an ambient air temperature reading, added 30°, converted it to pressure, and charged by head pressure. Now, if a technician converts an R-502 system to HP80 and uses ambient temperature plus 30°, the system will be grossly undercharged. HP80 operates at a 40-psi higher head pressure than 502. HP62 operates at a 20-psi higher head pressure. Discharge temperatures will also vary depending on which refrigerant you convert to.

Most of the new refrigerants increase a system’s capacity, but not all. For example, R-134a operates at 10% less capacity than R-12. The chance of this affecting your system is minimal, but keep in mind, capacity is affected.

DuPont supplies information on conversions and what to expect with new refrigerants. These pamphlets are must-have tools for technicians converting older systems to use replacement refrigerants. For more information, call DuPont at 800-235-7882.

Publication date: 10/16/2000