52
Timed Override Hours (
SCH.O
→
OV.EX) — This displays
the current number of hours left in an override. It is possible to
cancel an override in progress by writing “0” to this variable,
thereby removing the override time left.
SPT Override Enabled? (
SCH.O
→
OV.SP) — If a space sen-
sor is present, then it is possible to override an unoccupied
period by pushing the override button on the T55 or T56
sensor. This option allows the user to disable this function by
setting this configuration to NO.
Alarm Handling — There are a variety of different alerts
and alarms in the system. Alerts are indicated by Tnnn (where
nnn is the alert number) on the display and generally signify
that the improperly functioning circuit can restart without hu-
man interaction. If an alarm occurs, indicated by Annn (where
nnn 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 min-
utes. 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 be deactivated, 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 net-
works 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. The default is YES.
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 con-
figuration 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 partic-
ular condition.
NOTE: 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 43. 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 on page 36.
Complete Unit Stoppage — There are several condi-
tions that can cause the unit not to provide heating or cooling:
• 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.
• Cooling and heating loads are satisfied.
• Programmed occupancy schedule.
• General power failure.
• Tripped CB1, CB2, or CB3 (24-volt transformer circuit
breakers).
• Blown fuse (FU1 or FU2)
• Unit is turned off through the CCN network.
• If supply-air temperature is less than the Minimum SAT
Lower Level (SAT.L) configuration value, unit cannot
cool.
• If outdoor-air temperature is less than the Compressor
Lockout Temperature (CA.LO, CB.LO, CC.LO) configu-
ration value, unit cannot cool.
• If outdoor-air temperature is greater than the Heating
Lockout Temperature (HT.LO) configuration value, unit
cannot heat.
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