FORM 155.21-O1 (615)
19
JOHNSON CONTROLS
2
Purge Mode Changes
When the purge mode is changed, 7SOL and 8SOL are
closed. If NOT closed the purge pump will continue to
run an additional 65 seconds, if it was running.
If the purge mode is changed to "REPAIR", it is possible
to purge either the purge tank or the evaporator-absorber
shell. Another option could be to test the purge line for
any leaks and verify pump performance without purg-
ing the unit.
• Purging the purge tank: open VP2, close VP4.
• Purging the shell: Close VP2 and open VP4 (VP2 could
be open if it desired to make a faster vacuum).
• Testing the purge line or the purge devices; Close
VP2, and VP4.
Auto-Decrystallization Process
The auto-decrystallization process is triggered when the
ADC pipe temperature sensed by RT2 is greater than
160°F (71°C) and 3F float/level switch is closed (enough
refrigerant level exists for the refrigerant pump). The
auto-decrystallization line provides an alternate path
for the strong solution from the generator.
If a situation starts to develop such that solution concen-
tration from the generator is excessively high, solution
crystals will start to build on the shell side of the heat
exchanger. This will restrict the flow through the nor
-
mal line of solution return from the generator, then the
solution level will increase in the overflow box until it
reaches the auto-decrystallization line.
• This process sets the control valve opening to 50%
to decrease the concentration in the solution.
• Open Stabilizer Valve (2SOL) valve 2 minutes every
10 minutes.
• 3F float switch is closed (enough refrigerant level
exists for the refrigerant pump).
• If 3F level switch opens, stops the auto-decrystal
-
lization process and starts the limited auto-decrstal-
lization process.
• Reviews the temperature at RT2 every 10 minutes,
if it is less than 150°F (65°C), the control assumes
that the unit has been decrystallized and returns to
running mode.
•
During a soft shutdown, if the unit were to go into
an ADC mode, and the unit control valve is greater
than 50% open, the valve will be immediately be
driven to the 50% position. The soft shutdown will
continue from the 50% position. The unit will go
into a mandatory 6 minute dilution cycle if shutdown
during ADC.
Limited Auto-decrystallization
The limited auto-decrystallization process is triggered
when the temperature sensed by RT2 is greater than
160°
F (71
°C)
, and 3F float switch is open (insufficient
refrigerant level for the refrigerant pump).
• This process sets the valve opening to 50% to de
-
crease the concentration in the solution.
• Monitors 3F and 1F level switches, if both level
switches are closed, stops the limited decrytalliza-
tion process and starts the normal auto-decrytalli-
zation process.
• This process lasts until the 10 minute ADC timer that
was running when Limited Auto-decrystalization
started has completed.
Secondary Limited Auto-decrystallization
The secondary limited auto-decrystallization process is
called by the limited auto-decrystallization process when
it finishes and the temperature sensed by RT2 is greater
than 150°F (65.5°C), and the 3F level switch is open.
• This process closes the control valve, because the
machine is NOT capable of adding refrigerant to
the solution via 2SOL.
• Monitors 3F and 1F level switches, if both level
switches are closed, stops the secondary limited
auto-decrystallization process and starts the auto-
decrystallization process.
• This process last 15 minutes. If the temperature
sensed by RT2 is less than 150°F, the control as-
sumes that the unit has been decrystallized and
returns to running mode, if NOT, the control sets
the machine in safety shutdown.
UNIT OPERATION UNDER POWER FAILURE CON-
DITION USING AN EMERGENCY POWER SUPPLY
When the chiller has an emergency power supply, this
feature helps prevent crystallization if there is a power
failure. This feature manages the unit in three states:
• The unit is already diluted
• The unit is NOT diluted and it is possible to perform
a limited dilution cycle
• The unit is NOT diluted and it is NOT possible to
perform a limited dilution cycle because there was
a safety shutdown that does NOT allow the starting
of the solution pump.
All pumps are turned OFF and all valves are closed,
the control does NOT allow any manual operation of
the machine and waits until the unit has normal power
supply. After that, the unit is ready to start.
