JOHNSON CONTROLS
186
FORM 150.67-NM1
ISSUE DATE: 4/28/2017
SECTION 8 – UNIT OPERATION
The microprocessor will sequence compressors load
and unload systems according to Table 19. The micro-
processor will lead/lag compressors within each circuit
to maximize individual compressor run time for the
purpose of lubrication. It will also prevent the same
compressor from starting 2 times in a row. The micro-
processor will not attempt to equalize run time on indi-
vidual compressors within a system.
Each compressor in a system will be assigned an ar-
bitrary number 1, or 2. The non-running compressor
within a system with the lowest priority number will
always be the next compressor to start. The running
compressor with priority number 1 will always be the
next compressor to shut off. Whenever a compressor
is shut off, the priority numbers of all compressors
in each system will be decreased by 1 with the wrap
around. This control scheme assures the same com-
pressor does not repeatedly cycle ON and OFF.
ANTI-RECYCLE TIMER
The programmable anti-recycle timer assures that sys-
tems do not cycle. This timer is programmable under
the PROGRAM key between 300 and 600 seconds.
Whenever possible, to reduce cycling and motor heat-
ing, the anti-recycle timer should be adjusted to 600
seconds. The programmable anti-recycle timer starts
the timer when the first compressor in a system starts.
The timer begins to count down. If all of the compres-
sors in a circuit cycle OFF, a compressor within the cir-
cuit will not be permitted to start until the anti-recycle
timer has timed out. If the lead system has run for less
than 5 minutes, 3 times in a row, the anti-recycle timer
will be extended to 10 minutes.
ANTI-COINCIDENCE TIMER
This timer is not present on single-system units. Two
timing controls are present in software to assure com-
pressors within a circuit or between systems, do not
TABLE 18 -
RETURN CHILLED LIQUID CONTROL FOR 4 COMPRESSORS (6 STEPS)
*STEP
COMPRESSOR
COMPRESSOR ON POINT
COMPRESSOR OFF POINT
0
0
SETPOINT
SETPOINT
1
1 W/HGB
SP + CR/8 (NOTE 1)
SETPOINT
2
1 NO HGB
SP + CR/4
SP + CR/8
3
2
SP + 2*CR/4 (NOTE 2)
SP + CR/4
4
2
SP + 2*CR/4
SP + CR/4 (NOTE 3)
5
3
SP + 3*CR/4
SP + 2*CR/4
6
4
SP + CR
SP + 3*CR/4
Notes:
1. Step 1 is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during pumpdown.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
* STEP can be viewed using the OPER DATA key and scrolling to COOLING DEMAND.
TABLE 19 -
RETURN CHILLED LIQUID CONTROL FOR 4 COMPRESSORS (6 STEPS)
LEAD SYSTEM
LAG SYSTEM
STEP
COMP 1
COMP 2
-
COMP 1
COMP 2
-
0
OFF
OFF
-
OFF
OFF
-
1
ON + HG
OFF
-
SEE NOTE 1
OFF
OFF
-
2
ON
OFF
-
OFF
OFF
-
3
ON
OFF
-
SEE NOTE 2
ON
OFF
-
4
ON
ON
-
SEE NOTE 3
OFF
OFF
-
5
ON
ON
-
ON
OFF
-
6
ON
ON
-
ON
ON
-
NOTES
1. Step is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during pumpdown. For Leaving Chilled
Liquid Control the Hot Gas Bypass solenoid is energized only when the lead compressor is running and the LWT less than SP, the Hot Gas
Bypass solenoid is turned OFF when the LWT more than SP plus CR/2.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
Summary of Contents for YCAL0019
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