Servicing, Troubleshooting CPRs

July 2, 2004
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Crankcase pressure regulators (CPRs) are designed to prevent a compressor motor from overloading when its crankcase pressure rises above its design working pressure. CPRs are common accessories added on to many low-temperature refrigeration applications, such as walk-in and reach-in freezers. (See "Crankcase Pressure Regulators," June 7.)

The control set point of a CPR will need to be adjusted on the start-up of a new system or any time the valve is replaced. Always refer to the instructions provided by the manufacturer when adjusting these valves. If the manufacturer's instructions are not available, then these guidelines can be helpful.

  • Keep the system off long enough to allow the pressures to stabilize and the evaporator pressure to reach a high level. This is one that would simulate the pressure during or after a defrost period, or the initial start-up of the case.

  • Turn the adjustment screw on the valve all the way out. Normally turning the screw counterclockwise does this. This allows the valve to be set to an initial low setting.

  • Start the system and observe both the crankcase and the amperage draw of the compressor.

  • Slowly turn the adjustment screw in until the amperage draw reaches the maximum allowed by the compressor manufacturer. Normally turning the screw clockwise does this.

    This should allow a technician to achieve an acceptable set point for the valve.

    Some systems may have two CPRs that are piped in parallel. When adjusting these valves, both valves will need to be adjusted at the same time and at the same rate. This will ensure that the load is divided equally across both valves.

    Troubleshooting CPR valves is rather simple. Either the valve will regulate or fail to regulate the proper outlet pressure. If the valve fails to regulate the proper outlet pressure, it is usually best to just replace it.

    There are very few field repairs that can be made on these valves. Many times the problem is the result of foreign material (such as solder/brazing material or dirt) that is lodged within the valve.

    On occasion it may be possible to dislodge the foreign material by turning the adjustment all the way in with the system running. This will open the valve all the way and may dislodge the foreign material. If this fails to resolve the problem, then replace the valve.

    Another possible problem that can occur on the valves is a refrigerant leak that develops around the spring housing. When this occurs, it is best to replace the valve rather than trying to repair it in the field.

    These valves can be installed in any position, as long as there is sufficient room to make the necessary adjustments on start-up. When installing a CPR valve, always wrap the body in a wet cloth and direct the flame away from it to prevent warping of the interior components. Also, if there is a Schrader core on the inlet of the valve, make sure to remove it to prevent damage to its gaskets.

    Joe Marchese is owner of Coldtronics, Pittsburgh. He can be reached at 412-734-4433, www.coldtronics.com, or joe@rhvactools.com.

    Publication date: 07/05/2004

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