31
Consider the following values: Cool Demand = 0.9, change
in Cool Demand = 0.2, Cool Thermal Lag = 1.0, and Cool
Demand Positive Level = 1.0. Because 0.9 + 0.2*1.0 is greater
than 1.0, a stage of cooling would be added. This method of
adding a stage can only be used after the compressor settling
time has expired (SAT.T) and trend in SAT is increasing or
slowly decreasing. This method of adding a stage of cooling
can not be used again until a stage of cooling has been
removed. Additional stages of cooling can be added whenever
Cool Demand is greater than CL.PD + 0.5 and the SAT is
increasing at rate greater than –0.3 F/min.
The unit will remove a stage of cooling whenever the Cool
Demand (SPT – set point) is less than the SPT Cool Demand
Negative Level (CL.ND) plus the change in Cool Demand
times the Cool Thermal Lag (C.LAG). Consider the following
values: Cool Demand = –0.9, change in Cool Demand = –0.2,
Cool Thermal Lag = 1.0, and Cool Demand Negative Level =
–1.0. Because –0.9 + –0.2*1.0 is less than –1.0, a stage of cool-
ing would be removed. This method of removing a stage can
only be used after the compressor settling time has expired
(SAT.T) and the trend in SAT is decreasing or slowly increas-
ing. This method of removing a stage of cooling cannot be used
again until a stage of cooling has been added. Additional stages
of cooling can be removed whenever the Cool – Demand is
less than CL.ND –0.5 and the SAT is increasing at rate less
than 0.2 F/min.
Space Temperature Sensor Calibration and
Trim —
On units with Version 2.1 software or later, the space
temperature sensor (SPT) can be calibrated. The sensor can be
calibrated by entering data using either the ComfortLink™ dis-
play or by using Service Tool. The SPT calibration information
is found under CALB submenu of Temperatures when using
the Scrolling Marquee, or under the maintenance table
SENS_CAL when using Service Tool. When using either
method, the user can calibrate the sensor by entering the correct
space temperature at SPT.C (display) or SPT_CAL (Service
Tool). The software will automatically calculate the trim value
SPT.T (display) or SPT_OFF (Service Tool). The space tem-
perature should be measured with an accurate temperature
measuring device. The user can also calibrate the sensor by en-
tering the trim value directly. The trim value should be positive
when the SPT sensor is reading low and it should be negative
when the SPT is reading high.
If SPT if forced (T58 sensors) or failed, the sensor cannot be
calibrated. In general, the SPT should be calibrated only when
the space is near its expected operating temperature. If the cali-
bration value is refused by either the Scrolling Marquee or its
CCN table, calibration is currently not being allowed by the
software. The SPT Trim can be set at any time.
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 with-
out 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 min-
utes. This feature reduces the likelihood of false alarms causing
a properly working system to be shutdown 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 shutdown. 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
5 minutes with no detectable problems before the strike counter
will be reset to zero.
Operators with CCN networks might not want to be notified
of “striking” alerts until a circuit has been shut down because
of three alerts. If the operator sets A.NOW (Alarm Now) to
NO, alerts will not be announced until a circuit is permanently
shut down. This implies that alarm will not be broadcast on the
CCN network or listed on the display until a permanent shut-
down alarm occurs.
The status of A.NOW is ignored during Service Test mode
because it is presumed that the service technician will want to
be notified of any alerts or alarms immediately. So as not to
confuse a monitor center, the words “SERVICE TEST” are
inserted into every alarm message while the unit is operating in
Service Test Mode. The alarm output relay can be configured
using the Scrolling Marquee under ALRM in the configuration
menu or by using the ALARMOUT table via Service Tool.
This configuration allows the user to decide whether or not the
alarm output will activate when a particular set of alarms oc-
curs. (See Appendix A, ALARMOUT table.)
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 Tables 21 and
27. 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 12.
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 schedule.
•
General power failure.
•
Tripped CB1, CB2 or CB3 (24-volt transformer circuit
breakers).
•
Blown fuse (1 or 2).
•
Unit is turned off through the CCN network.
•
If unit cannot cool, supply air temperature may be less
than variable MIN.L (Default = 48 F).
Single Circuit Stoppage —
If a single circuits stops
incorrectly, there are several possible causes. The problem
should be investigated using information from the alarm list.
See Table 27.
Service Analysis —
Detailed service analysis can be
found in Tables 28, 29, and 30 and in Fig. 13.
Restart Procedure —
Before attempting to restart the
machine, check the alarm list to determine the cause of the
shutdown. If the shutdown alarm for a particular circuit 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 circuit can operate in either Normal
mode or Service Test mode.
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