Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 126

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This is done to make a rough calibration of the high pressure
switch trip point. In most cases this allows the control to detect
a high head pressure condition prior to reaching the high pres-
sure 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 affect-
ed 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 3 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 2 strikes on the circuit and a compressor on the circuit turns
on and runs for 5 minutes straight with no failure, 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 reduced by Configuration  IAQ  PROG 
AC.SP as each compressor is staged on while running the com-
pressor auto-component test, this alert shall be logged. Recov-
ery is automatic. 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
CTRL  C.SHS ± Configuration  IAQ  PROG  AC.DB at the
-10 0 10
Fig. 17 — High Pressure/SCT Alarm Upper Envelope
range Run Status  EXVS 
20 30 40
SST (F)
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.
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
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.
A068 (Circuit A Suction Gas Thermistor Failure)
This alarm trips during a thermistor failure of the return gas
temperature sensor. It is used with MLV option only.
T072 (Evap. Discharge Reset Sensor Failure)
This sensor is responsible for third party reset of the cooling sup-
ply 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. Recovery
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)
Failure of this thermistor (Temperatures  AIR.T  OAT) will
disable any elements of the control which require its use. Econ-
omizer 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 require 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.
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the range Run Status  EXVS 
80