Compressor Stuck On Failure Alarms; Dual Chiller Thermistor Failure; Circuit A Discharge Pressure Transducer Failure; Circuit A Suction Pressure Transducer Failure - Carrier AquaSnap 30MPA Series Controls, Start-Up, Operation, Service, And Troubleshooting

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IMPORTANT: Prolonged operation in the wrong direction
can damage the compressor. Correct rotation can be veri-
fied by a gage set and looking for a differential pressure
rise on start-up.
IMPORTANT: If the CS is always detecting current, verify
that the compressor is on. If the compressor is on, check
the contactor and the relay on the MBB. If the compressor
is off and there is no current, verify the CSB wiring and
replace if necessary.
IMPORTANT: Return to Normal mode and observe com-
pressor operation to verify that compressor current sensor
is working.

COMPRESSOR STUCK ON FAILURE ALARMS

Circuit A A051, A052, A053 — Alarm codes 051, 052, and
053 are for compressors A1, A2, and A3. These alarms occur
when the CSB detects current when the compressor should be
off. When this occurs, the control turns off the compressor.
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 as follows:
1. If any of the compressors are diagnosed as stuck on and
the current sensor board is on and the request is off, the
control will command the condenser fans to maintain
normal head pressure.
2. The control will shut-off all other compressors.
The possible causes include welded contactor or frozen
compressor relay on the MBB.
To check out alarms A051 to A053:
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 CSB wiring.
5. Return to Normal mode and observe compressor opera-
tion to verify that compressor current sensor is working
and condenser fans are energized.
A060 (Cooler Leaving Fluid Thermistor Failure) — If the
sensor reading is outside the range of –40 to 240 F (–40 to
116 C) then the alarm will occur. The cause of the alarm is usu-
ally a faulty thermistor, a shorted or open thermistor caused by
a wiring error, or a loose connection. Failure of this thermistor
will shut down the entire unit.
A061 (Cooler Entering Thermistor Failure) — If the sensor
reading is outside the range of –40 to 240 F (–40 to 116 C) then
the alarm will occur. The cause of the alarm is usually a faulty
thermistor, a shorted or open thermistor caused by a wiring er-
ror, or a loose connection. Failure of this thermistor will shut
down the entire unit.
T062 (Condenser Leaving Fluid Thermistor Failure) — If
the sensor reading is outside the range of –40 to 240 F (–40 to
116 C) then the alert will occur. The cause of the alert is usually
a faulty thermistor, a shorted or open thermistor caused by a
wiring error, or a loose connection. Failure of this thermistor
will send out an alert only.
T063 (Condenser Entering Thermistor Failure) — If the sen-
sor reading is outside the range of –40 to 240 F (–40 to 116 C)
then the alert will occur. The cause of the alert is usually a
faulty thermistor, a shorted or open thermistor caused by a wir-
ing error, or a loose connection. Failure of this thermistor will
send out an alert only.
T068 (Circuit A Compressor Return Gas Temperature
Thermistor Failure) — This alert occurs if the RGT is config-
ured and the compressor return gas temperature sensor is out-
side the range of –40 to 240 F (–40 to 116 C). Failure of this
thermistor will shut down the appropriate circuit.
T073 (Outside Air Temperature Thermistor Failure) — This
alert occurs when the outside air temperature sensor is outside
the range of –40 to 240 F (–40 to 116 C). Failure of this therm-
istor will disable any elements of the control which requires its
use. The OAT must be configured.
T074 (Space Temperature Thermistor Failure) — This alert
occurs when the space temperature sensor is outside the range
of –40 to 240 F (–40 to 116 C). Failure of this thermistor will
disable any elements of the control which requires its use. The
cause of the alert is usually a faulty thermistor in the T55 or
T58 device, a shorted or open thermistor caused by a wiring er-
ror, or a loose connection. The SPT must be configured.
A077 (Circuit Saturated Suction Temperature Exceeds
Cooler Leaving Water Temperature) — This alarm occurs
when the saturated suction temperature (SST) is greater than
leaving water for 5 minutes. This alarm will occur if either the
suction pressure transducer reading, which is used to calculate
SST, or cooler leaving water is incorrect. Potential causes for
this alarm are loose wiring connection, sensor not located in
well, or bad Schrader fitting. Reset is manual.
T079 (Dual Chiller Thermistor Failure) — This alert occurs
when the dual chiller temperature sensor is outside the range of
–40 to 240 F (–40 to 116 C). Failure of this thermistor will dis-
able dual chiller operation and return to stand-alone operation.
The unit must be configured for dual chiller operation for this
alert to occur. 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. Reset is automatic.
A090 (Circuit A Discharge Pressure Transducer Failure) —
This alarm occurs when the pressure is outside the range of 0.0
to 667.0 psig (0.0 to 4599 kPag). A circuit cannot run when this
alarm is active. Use the scrolling marquee to reset the alarm.
The cause of the alarm is usually a faulty transducer, faulty 5-v
power supply, or a loose connection.
A092 (Circuit A Suction Pressure Transducer Failure)
This alarm occurs when the pressure is outside the range of 0.0
to 420.0 psig (0.0 to 2896 kPag). A circuit cannot run when this
alarm is active. Use the scrolling marquee to reset the alarm.
The cause of the alarm is usually a faulty transducer, faulty 5-v
power supply, or a loose connection.
T094 (Discharge Gas Thermistor Failure) — This alert oc-
curs for units which have the digital compressor installed on
circuit A. If discharge gas temperature is open or shorted, the
circuit will be shut off. The valid range for this thermistor is
–39.9 to 356 F (–39.9 to 180 C). The alert will reset itself when
discharge temperature is less than 250 F (121.1 C). The cause
of the alert is usually low refrigerant charge or a faulty
thermistor.
A110 (Circuit A Loss of Charge) — This alarm occurs when
the compressor is OFF and the discharge pressure is less than
26 psig (179.2 kPa).
A112 (Circuit A High Saturated Suction Temperature)
Alarm code 112 occurs when compressors in a circuit have
been running for at least 5 minutes and the circuit saturated
suction temperature is greater than 70 F (21.1 C). The high sat-
urated suction alarm is generated and the circuit is shut down.
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