Compressor will not Unload CHHA

Issue:

Compressor will not unload

Resolution:

• This chiller is actually unloading to 30% of full load.  It is very misleading to equate the compressor %RLA with the % of actual chiller capacity.  The recommendation is to look at the water temperature drop across the evaporator and compare it to the design temperature drop.
• Use the tests described in RTHA-SB-12 for RTHA and RTHB chillers.
• The RTHA and RTHB compressors were built as size "families" with a major and a minor size for each family.
  • A major size compressor would be 150, 215, 300, or 450 ton.
  • The minor size would actually be the same compressor and motor, but would be built with limited loading capability.
• These compressors are the 130, 180, 255, and 380 ton sizes. Both the minor and major sizes will have the same minimum ton capacity since they are essentially the same compressor.
• The minor size compressor is built with a stop to limit the maximum load of the compressor. So when comparing the turndown of a minor size compressor to a major size compressor in the same family, the minor will have less turndown than a major since the full load capacity of the minor size is already limited.
• Make sure that the wiring for the load/unload solenoid valves is correct. Refer the RTHA-SB-12 for the correct solenoid valve location.
• It is helpful to remember that for RTHA and RTHB compressors that the unload solenoid is always the solenoid valve closest to the schrader fitting on top of the compressor.

Notes:

Changes:

Other Question/Problem/Cause Statements:

• Compressor will not unload.
• Compressor will only unload to 60% RLA.

Facts:

• Water-Cooled Chiller (Pueblo) (RTHA)
• Water-Cooled Chiller (Pueblo) (RTHB)
• 380 Ton size
• R'Newal compressor.