Troubleshooting; Complete Unit Stoppage; Single Circuit Stoppage; Service Analysis - Carrier Weathermaster 48P2030-100 Controls, Start-Up, Operation, Service, And Troubleshooting

TROUBLESHOOTING

The scrolling marquee display shows the actual operating con-
ditions of the unit while it is running. If there are alarms or
there have been alarms, they will be displayed in either the cur-
rent alarm list or the history alarm list. The Service Test mode
allows operation of the compressors, fans, and other compo-
nents 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 that causes the unit to shut
down is active, diagnose the problem using the information
provided in the Alarms and Alerts section on page 118, 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 84-87 and
Fig. 17.

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 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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Humidi-MiZer Troubleshooting
Use the unit scrolling marquee or a CCN device to view the sta-
tus display 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 cor-
rected and cleared, then operation of the compressors, fans, and
Humidi-MiZer valves may be verified by using the Service Test
mode. See page 36. In addition to the Cooling Service Analysis
(Table 84), see the Humidi-MiZer Service Analysis (Table 85)
for more information.

Thermistor Troubleshooting

The OAT, SAT, RAT, CCT, T55, T56, and T58 temperature
sensors use 10K thermistors. Resistances at various tempera-
tures are listed in Tables 88 and 89. The DTT uses an 86K
thermistor. See Table 90. The RGTA uses a 5K thermistor. See
Tables 91 and 92.
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 control
board (MBB-J8 or RCB-J6). Connect the digital ohmmeter
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 tem-
perature (freezing point or boiling point of water) by measur-
ing the resistance of the thermistor with the terminal strip re-
moved from the control board. With the terminal strip plugged
back into the control board and the unit powered up, compare
the temperature determined from the resistance measurement
with the value displayed by the control in the Temperatures
menu using the scrolling marquee display.
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