York YD Mod D, Operation Manual, Page: 14 / 160

• Proximity Probe – Low Supply Voltage
• Discharge [#1/#2] – Low Temperature
• Discharge [#1/#2] – High Temperature
• Oil Pump [#1/#2] - Differential Pressure Calibration
• Oil Pump [#1/#2] – Pressure Transducer Out of Range
• Thrust Bearing [#1/#2] – Proximity Probe Clearance
• Thrust Bearing [#1/#2] - Proximity Probe Out of Range
When any of these conditions occur on a locked out compressor, they are displayed as Warnings.
This means a user knows that a condition exists on the locked compressor. The condition must be
corrected before the lockout is removed from the compressor. If it is not, the warning condition
reverts back to a safety as soon as the lockout is removed and this causes the chiller to trip.
Normal or single compressor mode
The Compressor Mode setpoint, available on the Capacity Compressor Cycling screen, is used to
select either Normal Mode or Single Compressor Mode. In Normal Mode, the second compressor
is brought on line to meet the load requirement as described previously. In Single Compressor
Mode, operation is restricted to one compressor. The lag compressor will not be brought online,
regardless of the load requirement.
When starting the chiller in Single Compressor mode, the operator does not designate which
compressor will run. Rather, the lead compressor is automatically selected by the software per the
present software operation. The software to select the lead compressor has not changed.
If Single Compressor Mode is selected while both compressors are running, a soft shutdown is
performed on the lag compressor. All faults for this inhibited compressor are continued to be
handled.
If the chiller is shutdown while running in Single Compressor mode, the software selects the lead
compressor as it normally does on a subsequent restart.
Compressor shutdown
There are two types of shutdowns performed on one or both compressors: Soft Shutdowns and
Fault shutdowns.
During a
Soft Shutdown , first the pre-rotation vanes are driven closed. When the vanes have
fully closed (or 210 seconds have elapsed, whichever occurs first), the discharge valve is then
driven closed. When the discharge valve has fully closed (or 40 seconds have elapsed, whichever
occurs first), the run signal to the compressor motor starter is de-energized and the compressor
enters Coastdown. If any discharge valve does not close within 40 seconds, a cycling shutdown is
performed and
Discharge #X – Valve Not Closed
is displayed.
If the lag compressor is taken off line due to a Low Load condition while both compressors are
running, as explained previously, a soft shutdown is performed on the lag compressor.
If one of the following shutdowns is initiated, a soft shutdown is performed simultaneously on all
running compressors:
• Operator Initiated Soft Shutdown at Keypad
• "Remote Stop”
• “Leaving Chilled Liquid temperature – Low Temperature”
• "Discharge Valve X – Valve Not Closed”
• “Multiunit – Contacts Open”
• “System Cycling (1 & 2) – Contacts Open”
Model YD Mod D with OptiView Control Center 14