AEC ACOA Series Air-Cooled Central Chillers - Manual (Page 28)

9. Compressor 1 unload solenoid 3SOL re-energizes through 4TAS-2 and 4 .
10. Compressor 1 unloads one bank of cylinders.
11. Circuit 2 oil and suction pressures rise to normal levels, and 3PS-2 and 9PS-2 terminate
the time open sequence.
Third stage capacity is now on line.
Step 4
12. Opstat 4TAS-4 closes as water temperature continues to rise. Compressor 1 unload
solenoid 3SOL de-energizes by 4TAS-NC4 open. Compressor 1 loads to 100%.
13. 100% unit capacity is not on line.
Run Cycle Sequence (Decreasing Load)
Step 4
1. Opstat 4TAS-4 opens as leaving water temperature starts to drop. Compressor 1 unload
solenoid 3SOL energizes through 4TAS-NC4 closed and N02 closed.
2. Compressor 1 unloads one bank of cylinders.
Third stage capacity is now on line (Compressor 1 at part load; Compressor 2 at 100%).
Step 3
1. Opstat 4TAS-3 opens as water temperature continues to drop. Relay 9CR de-energizes,
removing 4PS-2 bypass ( 4PS-2 now controls pumpdown). Compressor 1 unload solenoid
de-energizes through 4TAS-N02 open. Compressor 1 loads back up to 100%. Liquid line
solenoid 2SOL de-energizes and Circuit 2 refrigerant flow stops.
2. When suction pressure drops to the pumpdown limit, 4PS-2 opens and Compressor 2
stops. Circuit 2 pumpdown and off sequence is now complete, and all Circuit 2 controls
are back to standby status.
Second stage capacity is now on line (Compressor 1 at 100%).
Step 2
3. Opstat 4TAS-2 opens as water temperature continues to drop. Compressor 1 unload
solenoid 3SOL is energized through 4TAS-NC2 and NC4 closed. Compressor 1 unloads
one bank of cylinders.
First stage capacity is now on-line.
ACOA Series Air-Cooled Central Chillers
Page 27