Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting page 43

turned off internally. Cooling will not operate. This is usually
due to a network force on a non exposed CCN point. Reload
factory defaults or reinstall software on the MBB. Consult the
network manager if alert continues.
Alert Code T073 — Outdoor Air Temperature Thermistor
Failure
This alert occurs when the temperature is outside the range –40
to 240°F (–40 to 116°C). For all units, all ambient temperature
lockout limits for cooling and heating are ignored. For econo-
mizer equipped units, the economizer will not operate to pro-
vide cooling. The economizer will still operate for ventilation.
This alert resets automatically. The cause of the alert is usually
a faulty thermistor, a shorted or open thermistor caused by a
wiring error, or a loose connection.
Alert Code T074 — Space Temperature Thermistor Failure
This alert occurs when the temperature is outside the range –40
to 240°F (–40 to 116°C). This alert will only occur if the unit
control type is configured for Space Sensor (versus Thermo-
stat). Cooling and heating will not operate. For economizer
equipped units, the economizer will still operate for ventila-
tion. This alert resets automatically. The cause of the alert is
usually a faulty thermistor in the T-55, T-56, or T-58 device, a
shorted or open thermistor caused by a wiring error, or a loose
connection.
Alert Code T075 — Supply Air Temperature Thermistor Fail-
ure
This alert occurs when the temperature is outside the range –40
to 240°F (–40 to 116°C). Economizer cooling and adaptive
compressor staging cannot occur while this alarm is active.
This alert resets automatically. The cause of the alert is usually
a faulty thermistor, a shorted or open thermistor caused by a
wiring error, or a loose connection.
Alert Code T076 — Return Air Thermistor Failure
This alert occurs when the temperature is outside the range –40
to 240°F (–40 to 116°C). This alert will only occur if the unit is
configured for a return air sensor. Economizer differential dry
bulb control will not be allowed during this alert. This alert re-
sets automatically. The cause of the alert is usually a faulty
thermistor, a shorted or open thermistor caused by a wiring er-
ror, or a loose connection.
Alert Code T077 — Space Relative Humidity Sensor Failure
This alert occurs when the input is less than 3.5 mA and the
sensor is configured as installed. If a humidistat is not installed,
then dehumidification will not be functional. Check sensor and
wiring. This alert clears automatically.
NOTE: An ECB must be installed to use the space relative humid-
ity sensor.
Alert Codes T092 and T093 — Circuit Suction Pressure
Transducer Failure
Alert codes T092 and T093 are for circuits A and B respective-
ly. These alerts occur when the board does not properly read
the transducer voltage. A circuit cannot run when this alert is
active. Use the scrolling marquee to reset the alarm. The cause
of the alert is usually a faulty transducer, faulty 5-v power sup-
ply, or a loose connection.
Alert Codes T102 and T103 — Compressor Current Sensor
Failure
Alert codes T102 and T103 are for compressors A1 and B1, re-
spectively. These alerts can only occur if the unit is configured to
have compressor current
  
tion COOL CIR.A CS.A1 or CS.B1). These are not factory
installed so would have to be installed in the field and configured
accordingly. These alerts occur when the output of the current
sensor (CS) is a constant high value. These alerts reset automati-
cally. The cause of the alert is a wiring error, a loose connection,
or when configured to have the sensors when they are not actual-
ly installed. If the problem cannot be resolved and the CS board
sensors (Configura-
43
must be replaced, the CS board can be disabled while securing a
replaced board. A CS board is disabled by setting the corre-
sponding configuration to DISABLE.
Alert Codes T110 and T111 — Circuit Loss of Charge
Alert codes T110 and T111 are for circuits A and B respective-
ly. These alerts have "Service Test" text that will be displayed
if the alert occurred during service test. These alerts occur
when the compressor is OFF and the suction pressure is less
than 5 psig and OAT is greater than –5°F for 1 continuous min-
ute. Use the scrolling marquee to reset the alert. The cause of
the alert is usually low refrigerant pressure or a faulty suction
pressure. These alerts only occur when the compressor is OFF
because the low refrigerant pressure alarms (alerts T133 and
T134) handle this situation when the compressor is operating.
Alert Codes T126 and T127 — Circuit High Discharge Pressure
Alert codes T126 and T127 are for circuits A and B respectively.
These alerts have "Service Test" text that will be displayed if the
alert occurred during service test. These alerts occur when alerts
T051 and T055 are active while the appropriate condensing tem-
perature is greater than 150°F. These alerts reset automatically.
The cause of the alert is usually an overcharged system, high
outdoor ambient temperature coupled with dirty outdoor coil,
plugged filter drier, or a faulty high-pressure switch. See Alerts
T051 and T055 for diagnostic procedure.
Alert Codes T133 and T134 — Circuit Low Refrigerant Pres-
sure
Alert codes T133 and T134 are for circuits A and B respective-
ly. These alerts have "Service Test" text that will be displayed
if the alert occurred during service test. These alerts occur
when the compressor is operating and the evaporating tempera-
ture (converted from the suction pressure) is less than config-
ured low suction
  
tion COOL SST SST.1 (Low Suction — Level 1) or
SST.2 (Low Suction — Level 2) or SST.3 (Low Suction Level
3). The circuit SST value must be less than SST.1 (for 5 min-
utes), SST.2 (for 4 minutes), or SST.3 (for 3 minutes when us-
ing the economizer and 1.5 minutes when not using the econo-
mizer) for the alert to occur. When the outdoor temperature is
less than 40°F, the above values are reduced 1°F for every 2°F
the OAT is below 40°F. An alert will also occur if the circuit
SST value is less than SST.3 –5°F for 20 seconds and the out-
door temperature is above 40°F. All the above timers will reset
if the suction temperature rises above SST.O for 1 minute.
These alerts cause a strike for the respective circuit. If the OAT
is less than 10°F, the circuit will shut down without a strike.
These alerts will activate when the coil becomes frosted. How-
ever, during the 15-minute reset period, the coils will thaw and
strike should clear at restart if there is nothing else wrong with
the circuit. The alert resets automatically. The cause of the alert
is usually low refrigerant charge, dirty filters, evaporator fan
operating backwards, loose or broken belt, plugged filter drier,
faulty transducer, excessively cold return air, or stuck open
economizer when the ambient temperature is low.
Alert Codes T143 and T144 — Circuit Failure to Pressurize
Alert codes T143 and T144 are for circuits A and B respective-
ly. These alerts have "Service Test" text that will be displayed
if the alert occurred during service test. These alerts occur
when the compressor turns on and the suction pressure does
not drop at least 10 PSIG in the first 20 seconds. If the OAT is
less than 40°F (4.4°C) the suction only has to drop 5 PSIG.
This alert causes a strike for the circuit. The alert resets auto-
matically. The cause of the alert is usually compressor wiring
causing reverse rotation or a faulty compressor.
Alarm Code T153 — Real Time Clock Hardware Failure
The alert occurs when the RTC clock chip on the MBB is not re-
sponding. Time and date functions will not operate, such as local
occupancy schedules. The unit will default to 24/7 unoccupied
mode. Recovery is automatic but MBB board replacement may
control levels, Configura-