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A051 (Circuit A, Compressor 1 Stuck On Failure)
A052 (Circuit A, Compressor 2 Stuck On Failure)
A055 (Circuit B, Compressor 1 Stuck On Failure)
A056 (Circuit B, Compressor 2 Stuck On Failure) — Alarm
codes 051, 052, 055, and 056 are for compressors A1, A2, B1,
B2 respectively. These alarms occur when the current sensor
(CS) detects current when the compressor should be off. When
this occurs, the control turns off the compressor and logs a strike
for the respective circuit. Use the scrolling marquee to reset the
alarm.
If the current sensor board reads ON while the compressor
relay has been commanded OFF for a period of 4 continuous
seconds, an alarm is generated. These alarms are only moni-
tored for a period of 10 seconds after the compressor relay has
been commanded OFF. This is done to facilitate a service tech-
nician forcing a relay to test a compressor.
In addition, if a compressor stuck failure occurs and the cur-
rent sensor board reports the compressor and the request off,
certain diagnostics will take place.
1. If any of the 4 compressors are diagnosed as stuck on and
the current sensor board is on and the request is off, the
control will request the supply fan which will automati-
cally start building airflow control. Condenser fans will
also be commanded on to maintain normal head pressure.
2. Heating will be disabled while any one of the compres-
sors has this problem.
The possible causes are:
• welded contactor
• frozen compressor relay on MBB
To check out alarms 051, 052, 055, and 056:
1. Place the unit in Service Test mode. All compressors
should be off.
2. Verify that there is not 24 v at the contactor coil. If there is
24 v at the contactor, check relay on MBB and wiring.
3. Check for welded contactor.
4. Verify CS wiring.
5. Return to Normal mode and observe compressor opera-
tion to verify that compressor current sensor is working
and condenser fans are energized after compressor starts.
T064 (Circuit A Saturated Condensing Thermistor Failure)
T065 (Circuit B Saturated Condensing Thermistor Failure) —
Alert codes 064 and 065 are for circuits A and B, respectively.
This alert code is for 48/50AJ,AK,AW,AY units only. These
alerts occur when the saturated condensing temperatures (Tem-
peratures
REF.T
SCT.A and SCT.B) are outside the range
–40 to 240 F (–40 to 116 C). When this occurs, the control uses
the outdoor temperature (OAT) to control the outdoor fans. The
control will default to control based on the OAT sensor and will
turn on OFC.B when the ambient is above 65 F and off when
the ambient is below 50 F.
If the SCT and OAT sensors have all failed then the control
should turn on OFC.B when compressors are on.
The cause of the alert is usually a faulty thermistor, a
shorted or open thermistor caused by a wiring error, or a loose
connection.
T072 (Evaporator Discharge Reset Sensor Failure)
— If the
unit is configured to use the remote EDT 4 to 20 mA reset in-
put (Configuration
EDT.R
RES.S) and the sensor reading
is less than 2 mA then the alert will occur. When this occurs the
control will default to the internal set points. The sensor is
connected to the optional CEM module. For this sensor to be
used, the EDT 4 to 20 mA reset input (Configuration
EDT.R
RES.S) must be set to “enabled.”
T073 (Outside Air Temperature Thermistor Failure)
— This
alert occurs when the outside air temperature sensor (Temper-
atures
AIR.T
OAT) is outside the range –40 to 240 F
(–40 to 116 C). Failure of this thermistor (Tempera-
tures
AIR.T
OAT) will disable any elements of the control
which requires its use. Economizer control beyond the vent
position and the calculation of mixed-air temperature for the
sumZ algorithm will not be possible. This alert resets automati-
cally. The cause of the alert is usually a faulty thermistor, a
shorted or open thermistor caused by a wiring error, or a loose
connection.
T074 (Space Temperature Thermistor Failure)
— This alert
occurs when the space temperature sensor (Temperatures
AIR.T
SPT) is outside the range –40 to 240 F (–40 to
116 C). This alert will only occur if the unit is configured to use
a space temperature sensor. Configuration is done through
the Unit Control Type (Configuration
UNIT
C.TYP)
configuration. Failure of this thermistor (Temp era-
tures
AIR.T
SPT) will 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. This alert resets automatically.
The cause of the alert is usually a faulty thermistor in the T55,
T56, or T58 device, a shorted or open thermistor caused by a
wiring error, or a loose connection.
T075 (Return Air Thermistor Failure)
— This alert occurs
when the return air temperature sensor (Tempe ra-
tures
AIR.T
RAT) is outside the range –40 to 240 F (–40 to
116 C). The RAT is standard on all units and is located in the
return section near the auxiliary control box. This alert resets
automatically. The cause of the alert is usually a faulty thermis-
tor, a shorted or open thermistor caused by a wiring error, or a
loose connection.
Failure of this thermistor (Temperatures
AIR.T
RAT)
will disable 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
• return air temperature supply air reset
T076 (Outside Air Relative Humidity Sensor Failure)
—
This alert occurs when the outside air humidity sensor (In-
puts
REL.H
OA.RH) has a reading less than 2 mA. Failure
of this sensor will disable any elements of the control which re-
quires its use including economizer outdoor and differential en-
thalpy control. The OA.RH sensor is located in the economizer
hood and is used for control of the economizer. The sensor is a
loop powered 4 to 20 mA sensor. This alert resets automatical-
ly. The cause of the alert is usually a faulty sensor, a shorted or
open sensor caused by a wiring error, or a loose connection.
The unit must be configured to use the sensor through the Out-
side Air RH Sensor (Configuration
ECON
ORH.S)
setting.
T078 (Return Air Relative Humidity Sensor Failure)
— This
alert occurs when the return air humidity sensor
(Inputs
REL.H
RA.RH) has a reading less than 2 mA.
Failure of this sensor (Inputs
REL.H
RA.RH) will disable
IMPORTANT: If the compressor starts, verify that the
indoor and outdoor fans are operating properly.
IMPORTANT: If the CS is always detecting current, then
verify that the compressor is on. If the compressor is on,
check the contactor and the relay on the MBB. If the com-
pressor is off and there is no current, verify CS wiring and
replace if necessary.
IMPORTANT: Return to Normal mode and observe com-
pressor operation to verify that compressor current sensor
is working and condenser fans are energized after compres-
sor starts.