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103
TROUBLESHOOTING
The Navigator™ 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. The Service Test mode allows op
-
eration of the compressors, fans, and other components to be
checked while the unit is not operating.
Complete Unit Stoppage
There are several conditions that can cause the unit to not pro
-
vide heating or cooling. If an alarm is active, which causes the
unit to shut down, diagnose the problem using the information
provided in the Alarms and Alerts section on page 121, but
also check for the following:
• Cooling and heating loads are satisfied.
• Programmed schedule.
• General power failure.
• Tripped control circuit transformers circuit breakers.
• Tripped compressor circuit breakers.
• Unit is turned off through the CCN network.
Single Circuit Stoppage
If a single circuit stops incorrectly, there are several possible
causes. The problem should be investigated using information
from the alarm and alert list.
Service Analysis
Detailed service analysis can be found in Tables 72-75 and
Fig. 16.
Restart Procedure
Before attempting to restart the machine, check the alarm list
to determine the cause of the shutdown. If a 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 a 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.
Humidi-MiZer
®
Troubleshooting
Use the unit Navigator or a CCN device to view the status dis
-
play and the diagnostic display for information concerning
cooling operation with the Humidi-MiZer system. Check the
Current Alarms and Alarm History for any unresolved alarm
codes and correct. Verify Humidi-MiZer configuration settings
are correct for the site requirements. If alarm conditions are
corrected and cleared, then operation of the compressors, fans,
and Humidi-MiZer valves may be verified by using the Service
Test mode. See page 29. In addition to the Cooling Service
Analysis (Table 72), see the Humidi-MiZer Service Analysis
(Table 73) for more information.
Thermistor Troubleshooting
The OAT, RAT, EDT, LAT, T55, T56, and T58 temperature sen
-
sors use 10K thermistors. Resistances at various temperatures
are listed in Tables 76 and 77. The DTA1, LT-A and LT-B use an
86K thermistor. See Table 78. The ST-A1, ST-A2, ST-B1, ST-B2
and RTA1 use a 5K thermistor. See Tables 79 and 80.
THERMISTOR/TEMPERATURE SENSOR CHECK
A high quality digital volt-ohmmeter is required to perform
this check.
1. With the unit powered down, remove the terminal strip of
the thermistor being diagnosed from the appropriate con
-
trol board (MBB-J8 or RCB-J6). Connect the digital ohm
-
meter across the appropriate thermistor terminals in the
terminal strip.
2. Using the resistance reading obtained, read the sensor tem
-
perature from the appropriate sensor table.
3. To check thermistor accuracy, measure the temperature at
the thermistor location with an accurate thermocouple-
type temperature measuring instrument. Insulate thermo
-
couple to avoid ambient temperatures from influencing
reading. The temperature measured by the thermocouple
and the temperature determined from the thermistor resis
-
tance reading should be within 5°F (3°C) if care was taken
in applying thermocouple and taking readings.
If a more accurate check is required, unit must be powered down
and thermistor removed and checked at a known temperature
(freezing point or boiling point of water) by measuring the resis
-
tance of the thermistor with the terminal strip removed from the
control board. With the terminal strip plugged back into the con
-
trol board and the unit powered up, compare the temperature de
-
termined from the resistance measurement with the value dis
-
played by the control in the Temperatures menu using the Navi
-
gator display.
Transducer Troubleshooting
The electronic control uses 2 suction and 2 discharge pressure
transducers to measure the suction pressure of Circuits A and
B. The pressure/voltage characteristics of these transducers are
in shown in Tables 81 and 82. The accuracy of these transduc
-
ers can be verified by connecting an accurate pressure gage to
the second refrigerant port in the suction line.
Forcing Inputs and Outputs
Many variables may be forced both from the CCN and directly
at the local display. This can be useful during diagnostic testing
and also during operation, typically as part of an advanced
third party control scheme. See Appendix A and B.
NOTE: In the case of a power reset, any force levels in effect at
the time of the power reset will be cleared.
CONTROL LEVEL FORCING
If any of the following points are forced with a priority level of
7 (consult CCN literature for a description of priority levels),
the software clears the force from the point if it has not been
written to or forced again within the timeout periods defined
below:
Temperatures
AIR.T
OAT
Outside Air Temperature
30 minutes
Temperatures
AIR.T
RAT
Return Air Temperature
3 minutes
Temperatures
AIR.T
SPT
Space Temperature
3 minutes
Inputs
RSET
SP.RS
Static Pressure Reset
30 minutes
Inputs
REL.H
OA.RH
Outside Air Relative Humidity 30 minutes
Inputs
AIR.Q
OAQ
Outside Air Quality
30 minutes
Summary of Contents for WeatherExpert 48N2
Page 135: ...135 Fig 18 48 50N Typical Power Schematic Nominal 075 Ton Unit Shown ...
Page 136: ...136 Fig 19 48 50N Typical Power Schematic Nominal Ton 90 150 Units Shown ...
Page 137: ...137 Fig 20 48 50N Main Base Board Input Output Connections ...
Page 138: ...138 Fig 21 48 50N RXB EXB CEM Input Output Connections a48 9307 ...
Page 139: ...139 Fig 22 48 50N EXV SCB Input Output Connections a48 9308 ...
Page 140: ...140 Fig 23 48N Typical Modulating Gas Heat Unit Control Wiring ...
Page 141: ...141 Fig 24 50N Typical Electric Heat Unit Control Wiring ...
Page 144: ...144 Fig 27 48N Typical Gas Heat Section Wiring Nominal Ton 120 to 150 Units ...
Page 145: ...145 Fig 28 48 50N Typical Power Component Control Wiring 460 v ...
Page 146: ...146 Fig 29 48 50N Component Control Wiring 575 v Nominal Ton 075 to 150 Units ...
Page 147: ...147 Fig 30 48 50N Component Arrangement Power Box ...
Page 148: ...148 Fig 31 48 50N Component Arrangement Control Box ...
Page 240: ...240 APPENDIX D VFD INFORMATION CONT Fig G VFD Bypass Wiring Diagram WHEN USED ...