90
T075 (Return Air Thermistor Failure) — This alert occurs
when the return air temperature sensor (
Tempera-
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 ther-
mistor, 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
(
Inputs
→
REL.H
→
OA.RH
) has a reading less than 2 mA.
Failure of this sensor will disable any elements of the control
which requires its use including economizer outdoor and dif-
ferential enthalpy 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 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 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.
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
→
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 set point because
there is no offset available that may be applied to space temper-
ature. The alert will automatically clear. The unit must be con-
figured 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 447.2 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 range 0.5 to
134.5 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.
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
5 psig and the OAT is above –5 F for 1 continuous minute. The
alert will automatically clear when the suction pressure trans-
ducer reading is valid and greater than 15 psig. The cause of the
alert is usually low refrigerant pressure or a faulty suction pres-
sure 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.
There will be a start-up delay if the outside-air temperature
is too low. When the outdoor ambient is below 60 F, during ini-
tial start-up, saturated suction temperature will be ignored for a
period of 5 minutes. When
Temperatures
→
REF.T
→
SSTA
or
Temperatures
→
REF.T
→
SSTB
falls below 25 F for twenty
seconds continuously, the second compressor of the affected
circuit, if it exists, will be shut down with a local alert (P120,
P121) and a 10 minute timeguard will be added to the compres-
sor. If another 20 seconds passes and the saturated suction tem-
perature continues to be below 25 F, then compressor 1 will be
shut down and then an alert/alarm will be issued.
This failure follows a 3 strike methodology whereby the
first two times a circuit goes down entirely, an alert will be gen-
erated which keeps the circuit off for 15 minutes before allow-
ing the circuit to try again. The third time this happens, an
alarm 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/alarm.
To prevent nuisance alerts, P120 and P121 show up in the
alarm history and locally at the display but are not broadcast to
the network. To recover from these alerts, a 10-minute holdoff
timer must elapse and the saturated suction temperature must
rise above 29.32 F (54 psig). If recovery occurs, staging will be
allowed on the circuit again. Again, a “strike” is tied to the
circuit going off entirely, not reducing capacity and recovering.
Therefore it is possible that multiple P120 or P121 alerts may
be stored in alarm history but not broadcast.
If there are 1 or 2 strikes on the circuit and the circuit recov-
ers for a period of time, it is possible to clear out the strikes
thereby resetting the strike counter automatically. The control
must have saturated suction temperature greater than or equal
to 34 F for 60 minutes in order to reset the strike counters.
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
) and the circuit saturated suction is greater
than 60 F. The high saturated suction alert is generated and the
circuit is shut down. This condition resets after OAT drops by
5° F. Alert code 122 is for circuit A and 123 for circuit B.
Summary of Contents for WEATHERMAKER 48AJ020
Page 95: ...95 Fig 13 Typical Main Control Box Wiring Schematic A48 7787 ...
Page 96: ...96 TO NEXT PAGE Fig 14 Auxiliary Control Box Wiring Schematic A48 7294 ...
Page 98: ...98 Fig 15 Typical 2 Stage Gas Heat Wiring Schematic Size 051 and 060 Units Shown A48 6866 ...
Page 102: ...102 TO NEXT PAGE Fig 18 Typical Power Schematic Size 051 and 060 Units Shown A48 7298 ...
Page 104: ...104 Fig 19 Controls Option Wiring Schematic A48 7810 ...
Page 105: ...105 Fig 20 Small Chassis Component Location Size 020 035 Units A48 7301 ...
Page 106: ...106 Fig 21 Large Chassis Component Locations Size 036 060 Units A48 7302 ...