117
high-pressure switch trip, the upper horizontal portion of the
compressor operating envelope (see Fig. 22) is lowered 0.4 F
(3 psig). The control will not allow the compressor operating
envelope to be lowered below 153.0 F (630 psig).
This is done to make a rough calibration of the high pres-
sure switch trip point. In most cases this allows the control to
detect a high head pressure condition prior to reaching the high
pressure switch trip point.
When the trip occurs, all mechanical cooling on the circuit
is shut down until the HPS is cleared for 15 minutes. Any time
this alert occurs, a HPS trip strike will be logged on the affected
circuit. The alert is issued on HPS trip strikes 1 and 2, and an
alarm (A057, A058) is issued on strike 3.
An active alert or alarm will always cause the circuit to be
shut down. After 15 minutes, the circuit is allowed to restart if
there are fewer than 3 strikes on the affected circuit. If three
successive strikes occur the circuit will be locked out, requiring
a manual reset or power reset of the unit. The clearing of HPS
trip strikes during compressor operation is achieved through 5
continuous minutes of run time on the affected circuit. So, if
there are one or two strikes on the circuit and a compressor on
the circuit turns on and runs for 5 minutes straight with no fail-
ure, the circuit's HPS trip strikes are cleared.
NOTE: This alert/alarm is broadcast to the network.
T062 (Circuit A Suction Pressure Alert)
T063 (Circuit B Suction Pressure Alert) — Alert codes
062 and 063 are for circuits A and B respectively. If the circuit
suction pressure (Pressures
REF.P
SP.A, SP.B) is not re-
duced by Configuration
IAQ
PROG
AC.SP as each
compressor is staged on while running the compressor auto-
component test, this alert shall be logged. Recovery is automat-
ic. The reason for the alert is that circuit suction pressure did
not decrease enough when a compressor was staged on.
T064 (EXV A1 Superheat Outside Range)
T065 (EXV A2 Superheat Outside Range) — If the Circuit
A EXV superheat (Temperatures
REF.T
SH.A1, SH.A2)
is outside the range Run Status
EXVS
CTRL
C.SHS ±
Configuration
IAQ
PROG
AC.DB at the end of running
the EXVs auto-component test, this alert will be logged. Re-
covery is automatic. The reason for this alert is that the super-
heat set point is not being held by EXV.
T066 (EXV B1 Superheat Outside Range)
T067 (EXV B2 Superheat Outside Range) — If the Circuit B
EXV superheat (Temperatures
REF.T
SH.B1,
SH.B2) is outside the range Run Status
EXVS
CTRL
C.SHS ± Configuration
IAQ
PROG
AC.DB at the end of running the EXVs auto-component
test, this alert will be logged. Recovery is automatic. The
reason for this alert is that the superheat set point is not
being held by EXV.
T068 (Circuit A Return Gas Thermistor Failure)
— This
alarm trips during a thermistor failure of the return gas temper-
ature sensor. It is used with MLV option only.
T072 (Evaporator Discharge Reset Sensor Failure)
— This
sensor is responsible for third party reset of the cooling supply
air set point. If the unit is configured for “third party reset”
(Configuration
EDT.R
RS.CF=3) and this alert occurs, no
reset will be applied to the cooling supply air set point. Recov-
ery from this alert is automatic. Reason for error is either a
faulty sensor, wiring error, or damaged input on the CEM
board.
T073 (Outside Air Temperature Thermistor Failure)
— Fail-
ure of this thermistor (Temperatures
AIR.T
OAT) will dis-
able 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 pos-
sible. Recovery from this alert is automatic. Reason for error is
either a faulty thermistor, wiring error, or damaged input on the
MBB control board.
T074 (Space Temperature Thermistor Failure
) — Failure of
this thermistor (Temperatures
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.
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 (Temp era ture s
AIR.T
RAT) will disable any el-
ements of the control which requires its use. Elements of fail-
ure 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 control board.
T076 (Outside Air Relative Humidity Sensor Failure)
—
Failure of this sensor (Inputs
REL.H
OA.RH) will disable
any elements of the control which requires its use. Elements of
failure include: economizer outdoor and differential enthalpy
control. Recovery from this alert shall 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
REL.H
SP.RH) will disable any ele-
ments 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
REL.H
RA.RH) will disable any ele-
ments of the control which requires its use. Elements of failure
include economizer differential enthalpy control, humidifica-
tion, and dehumidification. Recovery from this alert is auto-
matic. Reason for error is either a faulty sensor, wiring error, or
damaged input on the CEM control board.
T079 (Mixed Air Relative Humidity Sensor Failure)
—
Failure of this sensor (Inputs
REL.H
MA.RH) will disable
any elements of the control which requires its use. Elements of
failure include humidification and dehumidification prognos-
tics. Recovery from this alert is automatic. Reason for error is
either a faulty sensor, wiring error, or damaged input on the
CEM control board.
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