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T073 (Outside Air Temperature Thermistor Failure)
Failure of this thermistor (Temperatures
disable any elements of the control which requires its use. Econo-
mizer control beyond the vent position and the calculation of
mixed air temperature for the SumZ algorithm will not be possi-
ble. Recovery from this alert is automatic. Reason for error is ei-
ther a faulty thermistor, wiring error, or damaged input on the
MBB control board.
T074 (Space Temperature Thermistor Failure)
Failure of this thermistor (Temperatures
disable any elements of the control which requires its use. If the
unit is configured for SPT 2 stage or SPT multi-stage operation
and the sensor fails, no cooling or heating mode may be chosen.
Recovery from this alert is automatic. Reason for error is either a
faulty thermistor in the T55, T56 or T58 device, wiring error, or
damaged input on the MBB control board.
T075 (Return Air Thermistor Failure)
Failure of this thermistor (Temperatures
able any elements of the control which requires its use. Elements
of failure include:
•
The calculation of mixed air temperature for sumZ control.
•
The selection of a mode for VAV units.
•
Economizer differential enthalpy or dry bulb control.
•
RAT offset control for dehumidification.
•
Return air temperature supply air reset.
•
Fan tracking for building pressure control.
Recovery from this alert is automatic. Reason for error is either a
faulty thermistor, wiring error, or damaged input on the MBB con-
trol board.
T076 (Outside Air Relative Humidity Sensor Failure)
Failure of this sensor (Inputs
any elements of the control which requires its use. Elements of
failure include: economizer outdoor and differential enthalpy con-
trol. Recovery from this alert will be automatic. Reason for error is
either a faulty sensor, wiring error, or damaged input on the CEM
control board.
T077 (Space Relative Humidity Sensor Failure)
Failure of this sensor (Inputs
elements of the control which requires its use. Elements of failure
include humidification and dehumidification. Recovery from this
alert is automatic. Reason for error is either a faulty sensor, wiring
error, or damaged input on the CEM control board.
T078 (Return Air Relative Humidity Sensor Fail)
Failure of this sensor (Inputs
elements of the control which requires its use. Elements of failure
include economizer differential enthalpy control, humidification,
and dehumidification. Recovery from this alert is automatic. Rea-
son for error is either a faulty sensor, wiring error, or damaged in-
put on the CEM control board.
T082 (Space Temperature Offset Sensor Failure)
When this failure occurs, there is no offset available that may be
applied to space temperature. Recovery from this alert is
automatic. Reason for error is either a faulty slider potentiometer,
wiring error, or damaged input on the MBB control board.
T090 (Circ A Discharge Press Transducer Failure)
T091 (Circ B Discharge Press Transducer Failure)
The associated circuit becomes disabled whenever this transducer
(Pressures
REF.P
DP.A, DP.B) fails. Recovery from this alert
is automatic. Reason for error is either a faulty sensor, wiring er-
ror, or damaged input on the MBB control board.
T092 (Circ A Suction Press Transducer Failure)
T093 (Circ B Suction Press Transducer Failure)
The associated circuit becomes disabled whenever this transducer
(Pressures
REF.P
SP.A, SP.B) fails. Recovery from this alert
AIR.T
OAT) will
AIR.T
SPT) will
AIR.T
RAT) will dis-
REL.H
OA.RH) will disable
REL.H
SP.RH) will disable any
REL.H
RA.RH) will disable any
is automatic. Reason for error is either a faulty sensor, wiring er-
ror, or damaged input on the MBB control board.
T110 (Circuit A Loss of Charge)
T111 (Circuit B Loss of Charge)
Alert codes 110 and 111 are for circuits A and B respectively.
These alerts occur when all the compressors on a circuit are OFF
and the suction pressure is less than 18 psig, if the OAT is above –
5°F for 1 continuous minute. The alert will automatically clear
when the suction pressure transducer reading is valid and greater
than 54 psig. The cause of the alert is usually low refrigerant pres-
sure or a faulty suction pressure transducer.
P120 (Circuit A Low Saturated Suction Temp. Comp Shutdown)
T120 (Circuit A Low Saturated Suction Temperature Alert)
A120 (Circuit A Low Saturated Suction Temperature Alarm)
P121 (Circuit B Low Saturated Suction Temp. Comp Shutdown)
T121 (Circuit B Low Saturated Suction Temperature Alert)
A121 (Circuit B Low Saturated Suction Temperature Alarm)
This alert/alarm is used to keep the evaporator coils from freezing
and the saturated suction temperature above the low limit for the
compressors.
When Temperatures
REF.T
SST.B is less than 20°F for 4 minutes, less than 10°F
for 2 minutes, less than 0°F for 1 minute, or less than –20°F for
20 seconds continuously, a compressor of the affected circuit
will be shut down with a local pre-alert (P120, P121) and a
15-minute timeguard will be added to the compressor. If the sat-
urated suction temperature continues to be less than 20°F for 4
minutes, less than 10°F for 2 minutes, less than 0°F for 1 minute,
or less than –20°F for 20 seconds continuously, another com-
pressor of the affected circuit, if it exists, will be shut down with
a local pre-alert (P120, P121) and a 15-minute timeguard will be
added to the compressor. This sequence will continue until the
last compressor on the circuit is shut down, at which time the cir-
cuit will be shut down with alert (T120, T121).
This failure follows a 3-strike methodology. When the circuit is
shut down entirely, an alert (T120, T121) is generated and a strike
is logged on the circuit. The Alert and strikes logged will automat-
ically reset if the saturated suction temperature remains above
29.4°F for 15 minutes. On the third strike, alarm (A120, A121)
will be generated, which will necessitate a manual reset to get the
circuit back running. It is important to note that a strike is called
out only if all compressors in the circuit are off at the time of alert.
To prevent nuisance alerts, P120 and P121 show up in the alarm
history and locally at the display, but are never broadcast to the
network. To recover from these pre-alerts, both a 15-minute
hold-off timer and saturated suction temperature rising above
29.4°F must occur. If recovery occurs, staging will be allowed
on the circuit once again. A strike is tied to the circuit going off
entirely, not reducing capacity and recovering. Therefore it is
possible that multiple P120 and P121 alerts may be stored in
alarm history but not broadcast.
T122 (Circuit A High Saturated Suction Temperature)
T123 (Circuit B High Saturated Suction Temperature)
This alert is for display purposes only. No action is taken by the
control when the alert occurs.
When Temperatures
REF.T
SST.B is greater than 70°F for Configuration
COOL
H.SST minutes, local alert T122 or T123 will occur. The
alerts automatically reset when the corresponding saturated suc-
tion temperature drops below 70°F.
P126 (Circuit A High Head Pressure, Comp Shutdown)
T126 (Circuit A High Head Pressure Alert)
A126 (Circuit A High Head Pressure Alarm)
P127 (Circuit B High Head Pressure, Comp Shutdown)
T127 (Circuit B High Head Pressure Alert)
A127 (Circuit B High Head Pressure Alarm)
This alert/alarm is used to keep the saturated condensing tempera-
ture below the compressor operating envelope outlined in Fig. 17.
127
REF.T
SST.A or Temperatures
REF.T
SST.A or Temperatures
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Table of Contents
Troubleshooting
