only the outdoor temperature to control the outdoor fans. If both the SCT and OAT fail, then circuit shutdown 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 is 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 Temperature 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 Failure
This alert occurs when the temperature is outside the range -40_to 240_F (-40_to 116_C). Differential dry bulb crossover control can not occur. Free cooling can only be controlled by the OAT and enthalpy. 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 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 alert 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 Test” text that will be displayed if the 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 Test” text that will be displayed if the 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_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 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 circuit. 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 Failure to Pressurize
This alert has “Service Test” text that will be displayed if the 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.
