Carrier AquaEdge 19DV Controls Operation And Troubleshooting page 21

RECYCLE CONTROL
The chiller may cycle off and wait until the load increases to
restart when the compressor is running in a lightly loaded con-
dition. This normal cycling is known as "recycle."
In cooling mode, a recycle shutdown is initiated when either of
the following conditions is true:
• Leaving chilled water temperature (or entering chilled wa-
ter temperature, if the EWT CONTROL OPTION is en-
abled) is more than 5°F (2.8°C) below the CONTROL
POINT.
• Leaving chilled water temperature (or entering chilled wa-
ter temperature, if the EWT CONTROL OPTION is en-
abled) is below the CONTROL POINT, and the chilled
water temperature difference is less than the RECYCLE
SHUTDOWN DELTA T.
In heating mode, a recycle cycle shutdown occurs when either
of the following conditions is true:
• Leaving condenser water temperature (or entering con-
denser water temperature, if the EWT CONTROL OP-
TION is enabled) is more than 5°F (2.8°C) below the
CONTROL POINT.
• Leaving condenser water temperature (or entering con-
denser water temperature, if the EWT CONTROL OP-
TION is enabled) is above the CONTROL POINT, and the
condenser water temperature difference is less than the
RECYCLE SHUTDOWN DELTA T.
NOTE: Recycle shutdown will not occur if the CONTROL
POINT has been changed by more than 1°F (0.56°C) within the
previous 5 minutes of operation.
When the chiller is in RECYCLE mode, the chilled water
pump relay remains energized so the chilled water temperature
can be monitored for increasing load. The recycle control uses
RECYCLE RESTART DELTA T to check when the compres-
sor should be restarted. In cooling mode, the compressor will
restart when the leaving chilled water temperature (or entering
chilled water temperature, if the EWT CONTROL OPTION is
enabled) is greater than the CONTROL POINT plus the RE-
CYCLE RESTART DELTA T for 5 consecutive seconds. In
heating mode, the compressor will restart when the leaving
condenser water temperature (or entering condenser water tem-
perature, if the EWT CONTROL OPTION is enabled) is less
than the CONTROL POINT minus the RECYCLE RESTART
DELTA T for 5 consecutive seconds.
RUNNING TIMERS AND COUNTERS
The PIC6 control maintains two run-time clocks: COMPRES-
SOR ONTIME and SERVICE ONTIME. COMPRESSOR
ONTIME indicates the total lifetime compressor run hours.
SERVICE ONTIME is a resettable timer that can be used to in-
dicate the hours since the last service visit or any other event.
A separate counter tallies compressor starts as TOTAL COM-
PRESSOR STARTS. All of these can be viewed on the RUN
TIMES screen. Both Ontime counters roll over to 0 at 500,000
hours. Manual changes to SERVICE ONTIME from the screen
are permitted at any time. If the controller is replaced, one op-
portunity before the first start-up with the new controller is
provided to set COMPRESSOR ONTIME and TOTAL COM-
PRESSOR STARTS to the last readings retained with the prior
controller.
The chiller also maintains a start-to-start timer and a stop-to-
start timer. These timers limit how soon the chiller can be start-
ed and are displayed on the system overview (home) and RUN
TIMES screens. They can be configured in the Configuration

Menu GENERAL CONFIGURATION screen. They must
expire before the chiller starts. If the timers have not expired,
the RUN STATUS parameter on the System Overview (Home)
and GENERAL PARAMETERS screen reads TIMEOUT.
WATER PUMPS CONTROL (FREEZE PREVENTION)
NOTE: In order to energize the chilled and condenser pump to
prevent evaporator and condenser tube freeze-up, the hydraulic
system should be enabled first (this can be configured in the Con-

figuration Menu FACTORY PARAMETERS screen).
Evaporator Freeze Prevention
When the evaporator saturated refrigerant temperature or evap-
orator refrigerant temperature is less than the EVAP REFRIG
TRIPPOINT + REFRIG OVERRIDE DELTA T (configurable
from 2°F to 5°F (1.1°C to 2.8°C) in the Configuration Menu

PROTECTIVE LIMIT CONFIG screen), an OVER-
RIDE—LOW EVAP REFRIG TEMP event will occur.
For any running status, if either of the conditions below is true
then unit will shut down under Alarm PROTECTIVE LIMIT -
EVAPORATOR FREEZE (State 261):
• Evaporator saturated refrigerant temperature or evaporator
refrigerant temperature is equal to or less than the EVAP
REFRIG TRIPPOINT (33°F [0.6°C] for water, (configu-
rable for brine in Configuration Menu
LIMIT CONFIG screen) plus 1°F (0.56°C).
• Leaving chilled water temperature or entering chilled wa-
ter temperature is less than EVAP REFRIG TRIPPOINT
plus 1°F (0.56°C).
NOTE: If the chiller is in recycle mode, it will transition to
TRIPOUT, and the CHILLED WATER PUMP will remain on.
The alarm will be clearable when the evaporator saturated re-
frigerant temperature, evaporator refrigerant temperature, leav-
ing chilled water temperature, and entering chilled water tem-
perature rise 5°F (2.8°C) above the EVAP REFRIG TRIP-
POINT.
Condenser Pump Control
The chiller will monitor the condenser pressure and may turn
on the condenser pump. If the condenser pressure is greater
than or equal to the COND PRESS OVERRIDE, and the enter-
ing condenser water temperature is less than 115°F (46.1°C),
the condenser pump will energize to try to decrease the pres-
sure and Process Alert - High Condenser Pressure Chiller Off
(Alert 157) will be generated. The pump will turn off when the
condenser pressure is 3.5 psi (24.1 kPa) less than the pressure
override and the condenser refrigerant temperature is less than
or equal to the entering condenser water temperature plus 3°F
(1.7°C).
NOTE: COND PRESS OVERRIDE is found in the Configura-

tion Menu PROTECTIVE LIMIT CONFIG screen.
Condenser Freeze Prevention
This control helps prevent condenser tube freezing by energiz-
ing the condenser pump relay. The PIC6 module controls the
pump and, by starting it, helps to prevent the water in the con-
denser from freezing.
When the chiller is off and condenser saturated refrigerant tem-
perature is less than or equal to the condenser freeze point, the
condenser water pump will be energized (Alarm State 262,
PROTECTIVE LIMIT - CONDENSER FREEZE). The fault
state will clear and the pump will turn off when the condenser
saturated refrigerant temperature is more than 5°F (2.7°C)
above the condenser freeze point and the entering condenser
water temperature is greater than the condenser freeze point. If
the chiller is in recycle shutdown mode when the condition oc-
curs, the controls will transition to a non-recycle shutdown.
CONTROL TEST
This feature allows the operator to quick-test the controls and
related hardware, including all unit-controlled outputs except
compressor output.
The unit must be off to run the test function. If the unit is on,
the test function cannot be accessed. The compressor can only
be started after the control test is finished. The test function
21

PROTECTIVE