Compressor Protection CGAF

Issue:

Compressor Protection

Resolution:

The Compressor Protection function monitors two conditions for each refrigerant circuit:

• Low Pressure Cutout
• Compressor Proving Switch.
  
  
   
• Low Pressure Cutout - The Chiller unit has two LPC switches per refrigerant circuit, a Loss of Charge pressure switch and an Evaporator Freeze Protection pressure switch. Both switches are connected in series and feed a Low Pressure Cutout (LPC) input for each refrigerant circuit. To avoid nuisance trips, when starting the first compressor under low ambient conditions, the Evaporator Freeze Protection pressure switch is bypassed for a time sufficient to allow the refrigerant pressure to build up. Whenever the LPC Bypass Relay is energized (closed), only the Evaporator Freeze Protection pressure switch is bypassed.
•     The Loss of Charge pressure switch is still    connected to the LPC input, and is continuously monitored    during this LPC Bypass Time. The Loss of Charge pressure    switch is used to protect the unit from running a compressor    with insufficient refrigerant to operate reliably. This    pressure switch, which should normally never trip, is    typically set to trip if the refrigerant pressure decreases    below 7 PSIG.     The Evaporator Freeze Protection pressure    switch is used to prevent the refrigerant from becoming cold    enough to cause the chilled solution in the Evaporator to    freeze, damaging the Chiller barrel. This pressure switch is    typically set to trip at a higher refrigerant pressure,    typically 20 to 45 PSIG depending on the designed operating    range of the unit.    When the LPC input opens on a refrigerant    circuit due to either of the two LPC switches, the    compressors on that circuit are shut off and locked out for a    LPC Restart Inhibit Time of 3 Minutes. The compressors are    allowed to restart a selected number of times after the LPC    Restart Inhibit Time has expired, provided the LPC input    closes within a specified time window.

• Compressor Proving Switch - Compressor Proving Switch Input which is used to provide a fault indication due to one or more of the following:
         
  • Overcurrent, short circuit protection       
    • High Pressure Cutout (HPC) indication       
    • Winding temperature       
    • Compressor Contactor Proving
       
    These fault indications are "direct acting", that is, a fault indication will result in the hardware external to the UCM initiating a compressor/circuit shutdown sequence independent of the UCM control. This input is used to ensure that the UCM recognizes that the refrigerant circuit has been shut off due to a fault indication and that it should not attempt to stage up the compressors on this circuit. The UCM also uses this input to generate the appropriate diagnostic reporting information.

     

    These inputs are wired in such a way that the Compressor Proving input is expected to be:   
         
  • Open when all compressors on the refrigerant circuit are off
  • Closed when at least one compressor on the refrigerant circuit is on.
     
  If the Compressor Proving Input detects a "fault", the UCM shall shut off and lock off both compressors on that refrigerant circuit, and set a Manual Reset diagnostic for that circuit.

Other Question/Problem/Cause Statements:

• Compressor Protection

Facts:

• Intellipak Air-Cooled Chiller 20-60

Original wave: case822