Compressor Shutdown - York YD Series Operation Manual

SECTION 1 – DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
Normal Or Single Compressor Mode
(Software version C.OPT.11.03.01.004 (or later))
The COMPRESSOR MODE Setpoint, available on the
Capacity Compressor Cycling Screen, is used to se-
lect either NORMAL Mode or SINGLE COMPRES-
SOR Mode. In Normal Mode, the second compressor
is brought on line to meet the load requirement as de-
scribed previously. In Single Compressor Mode, op-
eration is restricted to one compressor. The Lag com-
pressor will not be brought on line, 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 op-
eration. 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 Com-
pressor mode, the software selects the "Lead" com-
pressor 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 shut-
downs.
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 com-
pressor 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.
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If the Lag compressor is taken off line due to a Low
Load condition while both compressors are running (as
explained above), 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 Tem-
perature"
• "Discharge Valve X – Valve Not Closed"
• "Multiunit – Contacts Open"
• "System Cycling (1 & 2) – Contacts Open"
• "Control panel – Schedule"
If any faults other than those listed above occur during
a Soft shutdown, the Soft Shutdown is aborted, the run
signal to the compressor motor starter is de-energized
and the compressor(s) immediately enters "Coast-
down".
If an Operator initiates a "Local Stop" with the Key-
pad Rocker Switch or any fault occurs other than those
listed immediately above, a Fault Shutdown is per-
formed on all running compressors. Simultaneously,
the run signal to the compressor motor starter(s) is
de-energized, the compressor(s) enters "Coastdown",
and the Pre-rotation Vanes and Discharge Valve(s) are
driven closed.
FORM 160.69-O1
ISSUE DATE: 9/30/2012
JOHNSON CONTROLS