Low Pressure Cutout CGAC

Issue:

Low Pressure Cutout

Resolution:

CGAC, CCAC 

W7900 Pumpdown Timer:

• The pumpdown timer (1DL7) allows the compressor to pumpdown before shutdown on the chilled water flow switch 5K7 or 1S41.  The sequence of this shutdown is as follows:
  • 1K45 is de energized.  Its normally-open contacts open the circuit to the liquid line solenoid valve, initiated compressor pumpdown.
  • After the 1DL7 time delay elapses, the timed open contact to the 1DL7 open and power is removed from the W7900.  If power were not removed from the W7900, it would eventually identify these pumpdowns as low compressor pressure problems and it would lockout the compressors.
  • The best way to troubleshoot a thermal time delay relay is to put power on it while monitoring its contacts, to be sure the time delay function is working.  Then remove power to be sure it resets, after the bimetal disk has cooled.  The timer (1DL7) can be replaced by a solid-state timer with relay output.
• Verify the 1K45, 1K45 contacts, and associated circuitry.
• One way to test if this circuit is causing the problem; after a pumpdown, remove the 24VAC going to the W7900; re-initiate a start, then re-apply the power to the W7900 and check operation.

• Condition presents itself after the chiller terminates on a pumpdown.  The pumpdown may be initiated either by the flow switch opening, a manual pumpdown, or periodic pumpdown.

Notes:

See relevant IOM for particular chiller.

Similar action of controls on ALL W7900 controlled chillers.

Changes:

Other Question/Problem/Cause Statements:

• Low Pressure Cutout
• W7900

Facts:

• W7900 control tested and checked out; and working.
• Air-Cooled Chiller - Intellipak (CGAC)
• Compressor Chiller (PBL) (CCAA, CCAB, CCAC)