The Suction Line Filter-Drier method of cleaning up a system after a hermetic motor burnout is favored by service technicians and recommended by manufacturers throughout the HVAC and refrigeration industry. This method gives the most practical and positive protection of the new compressor, since the refrigerant lubricant mixture is filtered and purified just before it returns to the compressor. It is important that all contaminants remaining in the system be removed to prevent a repeat burnout of the new compressor. Suction Line Filter-Driers are designed specifically for clean-up after burnout with proven benefits.
The construction of the suction line filter-drier is not significantly different from the standard liquid line filter-drier. Both driers remove the important contaminants such as moisture, dirt, acid, and the products of lubricant decomposition. The suction line filter-drier utilizes the HH style charcoal core to obtain the maximum ability for lubricant clean-up and removing all types of contaminants.
The sealed models have an access valve (-T) at the inlet end to permit measuring the pressure drop during the first several hours of operation.
RSF shells have an access valve to measure pressure drop (see Parker Sporlan Bulletin 80-10).
Also, replaceable core Catch-Alls have a 1/4” female pipe connection (-G) in the endplate to permit the installation of an access valve to measure pressure drop.
If the proper style drier is not available, then a suction line filter-drier can be used in the suction or liquid line; and a liquid line filter-drier can be used in the suction line. The pressure drop characteristics of the two types of driers are essentially the same for a given line size.
The Catch-All Filter-Drier can be installed directly in the suction line by removing a portion of the line. After clean-up, the Catch-All Filter-Drier is generally left in the line. The cores in the replaceable model or RSF shell should be replaced with filter elements (RPE-48-BD or RPE-100) to obtain the lowest possible pressure drop. A hermetic motor burnout produces large amounts of acid, moisture, sludge and all types of lubricant decomposition materials. To obtain the maximum ability to remove all these various types of contaminants, the Sporlan HH style charcoal core is preferred. If the HH style core is not available, the standard cores may be used.
OEM recommendations stress the importance of lubricant in cleaning up a system after a motor burnout. The lubricant acts as a scavenger, collecting the acid, sludges, and other contaminants. Therefore, the service technician should check the color and acid content of the lubricant. It must be clean and acid free before the job is finished. The acid content can be checked with an acid test kit. For procedures for system clean-up please check pages 30 and 31 of Sporlan Bulletin 40-10.
This is frequently a difficult task. A lubricant sample can usually be obtained from the burned out compressor. To obtain repeated samples after the system is started up, install a trap in the suction line with an access valve in the bottom of the trap. This permits collecting the small amount of lubricant required for running an acid test. Another method is to build a trap with valves, and connections for charging hoses. Then refrigerant vapor from the discharge service valve is run through this trap and put back into the suction service valve. In a short time sufficient lubricant collects in the trap for analysis. For more information request Sporlan Form 40-141.
Most hermetic motors rely on refrigerant vapor for cooling. Any large pressure drop in the suction line could result in reduced flow of suction gas, and thus improper cooling of the new hermetic motor. Field experience has shown that if the filter-drier is properly sized, the pressure drop across it should not exceed the values given in the table below.
The pressure drop across the filter-drier should be checked during the first hour of operation to determine if the cores need to be changed. Any pressure loss in the suction line also reduces system capacity significantly. When an RSF shell or replaceable core type Catch-All is used, it is recommended that the cores be removed and filter elements installed when the clean-up job is complete. Obtaining a low pressure drop is particularly important for energy savings on supermarket refrigeration systems. Therefore, suction line filter-driers should be sized generously on these systems.
For more details on sizing and selection of filter-driers download Bulletin 40-10 (PDF)
For more articles on climate control:
Using P-T Analysis as a Service Tool for Refrigeration Systems