Carrier 48/50PD05 - Manual (Page 24)

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Loadshed Group Number (S.GRP)
This corresponds to the loadshed supervisory devices that reside
elsewhere on the CCN network and broadcast loadshed and redline
commands to its associated equipment parts. This variable will
default to zero which is an invalid group number. This allows the
loadshed function to be disabled until configured.
Redline Max Capacity (R.MXC)
This configuration tells the unit the maximum
cooling/dehumidification capacity allowed active during a
loadshed condition.
Redline Max Heat Stages (R.MXH)
This configuration tells the unit the maximum heating stages
allowed to be on during a redline condition.
Loadshed Max Heat Stages (R.MXH
This configuration tells the unit the maximum heating stages
allowed to be on during a loadshed condition.
The two Demand Limiting methods can be active simultaneously.
The lowest cool capacity and heat stage limits imposed by either
method are applied, and these “effective limits” are shown in the
points
CAPLIMIT (Run Status→COOL→LMT.C) and
HSTGLIMT (Run Status→HEAT→LMT.H), respectively. In
normal running mode, these limits will prevent capacity/stages
from being added, or capacity/stages to be removed, as applicable.
In test mode, these limits are ignored, and the user may continue to
operate at full load.
The point MODEDMDL (Run Status→MODE→D.LMT) is used
to show if any Demand Limiting is in effect that prevents the unit
from operating either cooling or heating at full--capacity.
IMPORTANT: MODEDMDL may reflect that staging is NOT
limited even though Loadshed is active or the network points are
being forced, if the capacity/stage limits in effect are not less than
the capacity/stages present in the unit.
If a more drastic mode of Demand Limiting is required, the
network point HVACDOWN (Run Status→MODE→HV.DN) can
be used to prohibit the unit from selecting any HVAC mode, thus
preventing the operation of the supply fan, compressors, condenser
fans, and heat stages. This point must also be forced, and is reset
automatically when not forced, and at POR.
Alarm Handling
There are a variety of different alerts and alarms in the system.
Alerts are indicated by TXXX (where XXX is the alert number) on
the display and generally signify that the improperly functioning
circuit can restart without human interaction. If an alarm occurs,
indicated by AXXX (where XXX is the alarm number), the
damaged circuit will generally not restart without an alarm reset via
the Scrolling Marquee display or CCN.
The response of the control system to various alerts and alarms
depends on the seriousness of the particular alert or alarm. In the
mildest case, an alert does not affect the operation of the unit in any
manner. An alert can also cause a “strike.” A “striking” alert will
cause the circuit to shut down for 15 minutes. This feature reduces
the likelihood of false alarms causing a properly working system to
be shut down incorrectly. If three strikes occur before the circuit
has an opportunity to show that it can function properly, the circuit
will strike out, causing the shutdown alarm for that particular
circuit. Once activated, the shutdown alarm can only be cleared via
an alarm reset.
However, circuits with strikes will be given an opportunity to reset
their strike counter to zero. As discussed above, a strike typically
causes the circuit to shut down. Fifteen minutes later, that circuit
will once again be allowed to run. If the circuit is able to run for 1
minute, its replacement circuit will be allowed to shut down (if not
required to run to satisfy requested stages). However, the
“troubled” circuit must run continuously for a user defined time
(Configuration→COOL→RST.C) with no detectable problems
before the strike counter will be reset to zero. Default value is 5
minutes.
CCN Alarm Broadcast
Operators of CCN networks might not want to be notified of
“striking” alerts for refrigerant circuits until the circuit has been
shut down due to 3 strikes. Set the cooling configuration of Alert
Each Strike (Configuration→COOL→ALM.N on display,
ALM_NOW on CCN) to YES to broadcast each circuit strike alert.
Set Alert Each Strike to NO to broadcast only circuit shut down.
Alert Each Strike configuration is ignored during Service Test and
all alerts are broadcast.
Alarm Relay Output
The alarm relay output is a normally open 24 vac output between
field connection terminal board terminals C and X. Selection of
which alerts and alarms will result in closing of the alarm relay
may be set in the Alarm Relay Configuration
(Configuration→ALM.O). Setting a configuration to YES will
result in the alarm output relay, ALRM, status of ON and 24 vac
between C and X when that particular condition is in an alarm
state. Setting a configuration to NO will result in no action by the
alarm output relay for that particular condition.
IMPORTANT: An accessory filter switch can be used along with
the alarm relay output function to indicate dirty filter service need.
See the Troubleshooting section for more information on viewing,
diagnosing, and clearing alerts and alarms.
TROUBLESHOOTING
The Scrolling Marquee display shows the actual operating
conditions of the unit while it is running. If there are alarms or
there have been alarms, they will be displayed in either the current
alarm list or the history alarm list. (See Table 8.) The Service Test
mode allows proper operation of the compressors, fans, and other
components to be checked while the unit is not operating. See
Service Test.
Complete Unit Stoppage
There are several conditions that can cause the unit not to provide
heating or cooling:
S If an alarm is active which causes the unit to shut down,
diagnose the problem using the information provided in Alarms
and Alerts section below.
S Cooling and heating loads are satisfied.
S Programmed occupancy schedule.
S General power failure.
S Tripped CB1 or CB2 (24-volt transformer circuit breakers).
S Unit is turned off through the CCN network.
S If outdoor-air temperature is less than the Compressor Lockout
Temperature (CA.LO) configuration value, unit cannot cool.
S If outdoor-air temperature is greater than the Heating Lockout
Temperature (HT.LO) configuration value, unit cannot heat.
Restart Procedure
Before attempting to restart the machine, check the alarm list to
determine the cause of the shut down. If the shutdown alarm for a
particular control function has occurred, determine and correct the
cause before allowing the unit to run under its own control again.
When there is problem, the unit should be diagnosed in Service
Test mode. The alarms must be reset before the control function
can operate in either Normal mode or Service Test mode.
Control Module Communication
Red LED
Proper operation of the MBB, ECB and AUX1 control boards can
be visually checked by looking at the red status LEDs. When
operating correctly, the red status LEDs should blink in unison at a
rate of once every 2 seconds. If the red LED on the ECB and
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