United Technologies Carrier Weathermaker 48A2, Controls, Start-Up, Operation, Service, And Troubleshooting

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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
Outside 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
any elements of the control which requires its use including
economizer differential enthalpy control, humidification, and
dehumidification.
The RA.RH sensor is located in the return air section near
the auxiliary control box. The sensor is a loop powered 4 to
20 mA sensor. This alert resets automatically. 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 con-
figured to use the sensor through the Outside Air RH Sensor
( Configuration

UNIT

SENS

RRH.S ) setting.
T082 (Space Temperature Offset Sensor Failure) — If the unit
is configured to use a space temperature sensor and is using a
T56 sensor with an offset potentiometer, then the alert will
occur if the potentiometer is outside the allowable range. The
control will default to the software applicable setpoint because
there is no offset available that may be applied to space tem-
perature. The alert will automatically clear. The unit must be
configured for one of the SPT control options through the Unit
Control Type ( Configuration

UNIT

C.TYP ) configuration.
T090 (Circuit A Discharge Pressure Transducer Failure)
T091 (Circuit B Discharge Pressure Transducer Failure) —
Alert codes 090, and 091 are for circuits A and B respectively.
These alerts occur when the unit is configured for pressure
transducers ( Configuration

UNIT

DP.XR ) and the pres-
sure is outside the range 0.0 to 667.0 psig. A circuit cannot run
when this alert is active. Use the scrolling marquee to reset the
alert. The cause of the alert is usually a faulty transducer, faulty
5v power supply, or a loose connection. Although the software
supports this option, it is not possible at the time of the writing
of this specification to order the optional discharge pressure
transducers.
T092 (Circuit A Suction Pressure Transducer Failure)
T093 (Circuit B Suction Pressure Transducer Failure) — Alert
codes 092, and 093 are for circuits A and B respectively. These
alerts occur when the pressure is outside the following ranges:
0.5 to 134.5 psig when SP.XR =0, 0.0 to 420.0 psig when
SP.XR =1. A circuit cannot run when this alert is active. Use the
scrolling marquee to reset the alert. The cause of the alert is
usually a faulty transducer, faulty 5 v power supply, or a loose
connection.
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
the compressor is OFF and the suction pressure is less than
18 psig and 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 pressure or a faulty
suction pressure transducer.
P120 (Circuit A Low Saturated Suction Temperature —
Compressor A2 Shutdown)
T120 (Circuit A Low Saturated Suction Temperature Alert)
A120 (Circuit A Low Saturated Suction Temperature Alarm)
P121 (Circuit B Low Saturated Suction Temperature —
Compressor B2 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.
T122 (Circuit A High Saturated Suction Temperature)
T123 (Circuit B High Saturated Suction Temperature) — Alert
codes 122 and 123 occur when compressors in a circuit have
been running for at least 5 to 30 minutes ( Configuration

COOL

H.SST ). This alert code occurs if the circuit satu-
rated suction temperature is greater than 65 F when one com-
pressor is running or 60 F when two compressors are running.
For all units, the high saturated suction alert is generated and
the circuit is shut down. Alert code 122 is for circuit A and 123
for circuit B.
LRTA High Saturated Condensing Temperature Alert/
Alarm
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 temperature be-
low maximum recommended compressor operating pressure.
This alert/alarm attempts to prevent the saturated condensing
temperature from reaching the high pressure switch trip point
by reducing the number of compressors operating on a circuit.
When the saturated condensing temperature on a circuit is
greater than 145 F, no compressors will be added to the circuit.
When temperatures REF.T , SCTA , or temperatures REF.T ,
SCTB rise above 150 F, a compressor of the affected circuit
will be immediately shut down with pre-alert (P126,P127) and
a 10-minute timeguard will be added to the compressor. If the
saturated condensing temperature remains above 150 F for 10
more seconds, another compressor of the affected circuit, if it
exists, will be shut down with pre-alert (P126, P127) and a 10-
minute timeguard will be added to the compressor. This se-
quence will continue until the last compressor on the circuit is
shut down, at which time the circuit will be shut down with
alert (T126, T127).
This failure follows a three strike methodology. When the
circuit is shut down entirely, an alert (T126, T127) is generated
and a strike is logged on the circuit. On the third strike, alarm
(A126, A127) will be generated which will necessitate a manu-
al 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 the alert.
To prevent nuisance alerts, P126 and P127 show up in the
alarm history and locally at the display, but are never broadcast
to the network. To recover from these alerts, both a 10-minute
hold off timer and saturated condensing temperature returning
under the compressor envelope must occur. If recovery occurs,
staging will be allowed on the circuit once again. Again, a
strike is tied to the circuit going off entirely, not reducing ca-
pacity and recovering. Therefore, it is possible that multiple
P126 and P127 alerts may be stored in alarm history but not
broadcast.
T128 (Digital Scroll High Discharge Temperature Alert)
A128 (Digital Scroll High Discharge Temperature Alarm)
— This alert/alarm is for units with a digital scroll compressor
only. The digital scroll compressor is equipped with a tempera-
ture thermistor that is attached to the discharge line of the com-
pressor. The alert occurs when the discharge temperature