79
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 cur-
rent alarm list or the history alarm list. The Service Test mode
allows proper operation of the compressors, fans, and other
components to be checked while the unit is not operating.
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
the Alarms and Alerts section on page 95, 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 Alarms and
Service Analysis —
Detailed service analysis can be
found in Tables 79-82 and in Fig. 19.
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.
Humidi-MiZer
®
Troubleshooting —
Use the unit
scrolling marquee or a CCN device to view the status display
and the diagnostic display for information concerning cooling
operation with the Humidi-MiZer system. Check the Current
Alarms and Alarm History for 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. By attaching temperature probes across the 3-way
valve, verify the temperature profiles satisfy the corresponding
mode setting. See page 23 for Service Test information. In
addition to the Cooling Service Analysis (Table 79), see the
Humidi-MiZer Service Analysis (Table 80) for more informa-
tion.
Thermistor Troubleshooting —
See Tables 83-85
for temperature vs. resistance data.
When replacing thermistors SCT.A and SCT.B, reuse the
original hardware. These thermistors must be clamped tightly
to the hairpins of the condenser.
The EDT, OAT, RAT, LAT, SAT, T55, T56, and T58 space
temperature sensors use 10K thermistors. Resistances at vari-
ous temperatures are listed in Tables 86 and 87.
The 48/50A2,A3,A4,A5 units with the optional variable ca-
pacity digital compressor are equipped with a digital scroll dis-
charge thermistor (DTT). The DTT is an 86K thermistor con-
nected to RXB at plug J6, terminals 3 and 4. The resistance
values are listed in Table 88.
THERMISTOR/TEMPERATURE SENSOR CHECK — A
high quality digital volt-ohmmeter is required to perform this
check.
1. Connect the digital voltmeter across the appropriate
thermistor terminals at the J8 terminal strip on the main
base board.
2. Using the voltage reading obtained, read the sensor tem-
perature from Tables 83-88.
3. To check thermistor accuracy, measure temperature at
probe location with an accurate thermocouple-type
temperature-measuring instrument. Insulate thermocou-
ple to avoid ambient temperatures from influencing
reading. Temperature measured by thermocouple and
temperature determined from thermistor voltage reading
should be close, 5° F (3° C) if care was taken in applying
thermocouple and taking readings.
If a more accurate check is required, unit must be shut down
and thermistor removed and checked at a known temperature
(freezing point or boiling point of water) using either voltage
drop measured across thermistor at the J8 terminal, or by deter-
mining the resistance with unit shut down and thermistor dis-
connected from J8. Compare the values determined with the
value read by the control in the Temperatures mode using the
scrolling marquee display.
Transducer Troubleshooting —
On 48/50A2,A3,
A4,A5 units, the electronic control uses 4 pressure transducers
to measure the suction and discharge pressure of circuits A and
B. The pressure/voltage characteristics of these transducers are
shown in Tables 89 and 90. The accuracy of these transducers
can be verified by connecting an accurate pressure gage to the
second refrigerant port in the suction line.
Summary of Contents for Carrier Weathermaker 48A2
Page 105: ...105 Fig 20 Typical Main Control Box Wiring Schematic 48 50A2 A3 A4 A5 Units...
Page 106: ...106 Fig 21 Typical Auxiliary Control Box Wiring Schematic...
Page 107: ...107 Fig 22 Typical 2 Stage Gas Heat Wiring Schematic Size 060 Units Shown a48 8357...
Page 108: ...108 TO NEXT PAGE Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown A48 7296...
Page 109: ...109 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown cont A48 8358...
Page 110: ...110 Fig 24 Typical Electric Heat Control Schematic 50 Series Size 060 Units Shown a50 8228...
Page 111: ...111 Fig 25 Typical Power Schematic 48 50A2 A3 A4 A5 060 Unit Shown...
Page 112: ...112 Fig 26 Typical Low Ambient Controls Option Wiring...
Page 113: ...113 Fig 27 Typical Small Chassis Component Location Size 020 035 Units...
Page 114: ...114 Fig 28 Typical Large Chassis Component Locations Size 040 060 Units...
Page 118: ...118 Fig 30 Economizer Control Board ECB1 and VAV Control Board ECB2 A48 7706...
Page 142: ...142 A48 3733 Fig 56 Main Burner Removal...
Page 176: ...176 APPENDIX C VFD INFORMATION cont Fig F Internal Enclosure Fan Replacement A48 7716...
