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only the outdoor temperature to control the outdoor fans. If both
the SCT and OAT fail, then circuit s hutdown alarm will occur also.
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 T066 -- Circuit A Saturated Suction Temperature
Thermistor Failure
This alert occurs when the unit’s suction transducers are 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 all units, if
both SCT and OAT fail, then circuit shutdown alarm will also
occur. For economizer equipped units, the economizer will not
operate to provide cooling. The economizer will still operate for
ventilation. The control will use condenser temperatures for
outdoor fan control. For units with CCH crankcase heat relay
control, the crankcase heat relay will be turned on if any
compressor i s off. 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). Cooling and heating will not operate. For
economizer equipped units, the economizer will still operate for
ventilation. 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 Temperatu re Thermistor
Failure
This alert occurs when the temperature is outside the range --40_ to
240_F(--40_ to 116_C). Economizer cooling and compressor
operation cannot occur while this alert is active. The unit will not
be allowed to enter cooling mode. 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 Fa ilure
This alert occurs when the temperature is outside the range --40_ to
240_F(--40_ to 116_C). Differential dry bulb crossover contro l
can not occur. Free cooling can only be controlled by the OAT and
enthalpy. This a lert 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 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.
IMPORTANT: An ECB must be installed to use the space
relative humidity sensor.
Alert Code T092 -- Circuit A Suction Pressure Transducer
Failure
This alert occurs 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 a lert
is usually a faulty transducer, faulty 5--v power supply, or a loose
connection.
Alert Code T102 -- Compressor A1 Current Sensor Failure
This Alert indicates that Current Sensing A1 (CS.A1) has been
enabled. The unit does not support the use of a current sensor at
this time. Change the CS.A1 to disable and this alert will clear and
not return.
(Configuration→COOL→CS.A1)
Alert Code T110 -- Circuit A Loss of Charge
This alert has “Service T e st” text that will be displayed if t he alert
occurred during service test. This alert occurs when the
compressor is OFF and the suction pressure is less than 5 psig and
OAT is greater than --5_F for 1 continuous minute. Use the
Scrolling Marquee to reset the alert. The cause of the alert is
usually low refrigerant pressure or a faulty suction pressure. This
alert only occurs when the compressor is OFF because the low
refrigerant pressure alarms (alert T133) handle this situation when
the compressor is operating.
Alert Code T126 -- Circuit A High Discharge Pressure
This alert has “Service Test” text that will be displayed if the alert
occurred during service test. This alert occurs when alert T051 is
active while the appropriate condensing temperature is greater than
150_F. This alert 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 Alert T051 for diagnostic procedure.
Alert Code T133 -- Circuit A Low Refrigerant Pressure
This alert has “Service T e st” text that will be displayed if t he alert
occurred during service test. This alert occurs when the
compressor is operating and the evaporating temperature
(converted from the suction pressure) is less than configured low
suction control levels, Configuration→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 minutes), SST.2 (for 4 minutes), or SST.3 (for 3
minutes when using the economizer and 1.5 minutes when not
using the economizer) for the alert to occur. When the outdoor
temperature is less than 40_F, the above values are reduced 1_Ffor
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
outdoor temperature is above 40_F. All the above timers will reset
if the suction temperature rises above SST.O for 1 minute. This
alert causes a strike for the respective c ircuit. This alert will activate
when the coil becomes frosted. However, during the 15--minute
reset period, the coils will thaw and strike should clear and 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 Code T143 -- Circuit A Failur e to Pressurize
This alert has “Service T e st” text that will be displayed if t he alert
occurred during service test. This alert occurs when the
compressor turns on and the difference between suction and
discharge pressure is less then the Ckt A Minimum Pressure
(Configuration→COOL→SST→PSI.D). The pressure difference
must be greater then PSI.D (default is 20 psi) after 60 seconds and
stay above it while running the compressor. This alert causes a
strike for the respective circuit. The alert resets automatically . The
cause of the alert is usually compressor wiring causing reverse
rotation or a faulty compressor.
Alert Code T153 -- Real Time Clock Hardware Failure
This alert occurs when the RTC clock chip on the MBB is not
responding. 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 be
necessary. Cycling power to the control and reconfiguring the time
and date should be tried before board replacement.
Alarm Code A154 -- Serial EEPROM Hardware Failure
The unit will completely shut down. The serial EEPROM chip on
the MBB, which stores the unit’s configuration, is not responding.
48/50PD