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This alert/alarm also attempts to prevent the saturated condensing
temperature from reaching the high pressure switch trip point by
reducing the upper horizontal portion of the compressor operating
envelope to a level slightly below the saturated condensing tem-
perature recorded upon a high pressure switch trip (T057, T058).
When Temperatures
REF.T
REF.T
SCT.B rise above the compressor operating envelope for
the corresponding Temperatures
tures
REF.T
SST.B, 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 satu-
rated condensing temperature remains above the envelope for
5 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 3-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 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 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 capacity 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 temperature
thermistor that is attached to the discharge line of the compressor.
The alert occurs when the discharge temperature thermistor has
measured a temperature above 268°F or the thermistor is short cir-
cuited. The digital scroll compressor will be shut down and alert
T128 will be generated. The compressor will be allowed to restart
after a 30-minute delay and after the thermistor temperature is be-
low 250°F.
If five high discharge temperature alerts have occurred within four
hours, alarm A128 will be generated which will necessitate a man-
ual reset to start the compressor.
A140 (Reverse Rotation Detected)
This alarm performs a check for correct compressor rotation upon
power up of the unit. The method for detecting correct rotation is
based on the assumption that there will be a drop in suction pres-
sure upon a compressor start if the compressor is rotating in the
correct direction.
A test is made once, on power up, for suction pressure change on
the first compressor of the first circuit to start.
Reverse rotation is determined by measuring suction pressure at 3
points in time:
•
5 seconds prior to compressor start.
•
At the instant the compressor starts.
•
5 seconds after the compressor starts.
The rate of suction pressure change from 5 seconds prior to com-
pressor start to compressor start (rate prior) is compared to the rate
of suction pressure change from compressor start to 5 seconds af-
ter compressor start (rate after).
If (rate after) is less than (rate prior minus 1.25), alarm A140 is
generated. This alarm will disable mechanical cooling and will
SCT.A or Temperatures
REF.T
SST.A or Tempera-
require a manual reset. This alarm may be disabled once the re-
verse rotation check has been verified by setting Configuration
COOL
RR.VF = Yes.
It is important to note that in Service Test mode, reverse rotation is
checked on every compressor start.
A150 (Unit is in Emergency Stop)
If the CCN point name "EMSTOP" in the System table is set to
emergency stop, the unit will shut down immediately and broad-
cast an alarm back to the CCN indicating that the unit is down.
This alarm will clear when the variable is set back to "enable".
A152 (Unit Down Due to Failure)
This alarm occurs whenever both cooling circuits are unavailable
to cool. Mechanical cooling is impossible due to a failure in the
system explained through other current alarms.
Possible problems are:
•
Plenum pressure switch trips on a return fan tracking unit.
•
The supply fan status alarms have been instructed to shut
down the unit.
•
Both circuits incapable of cooling due to multiple alerts of
compressors and/or pressure alerts.
•
A hardware failure of the main board's analog to digital
converter or EEPROM chip.
•
A critical storage failure in EEPROM has rendered the unit
inoperable.
•
The unit is configured for inlet guide vanes and the actua-
tor controlling the vanes is in fault.
Reset is automatic.
T153 (Real Time Clock Hardware Failure)
The RTC clock chip on the MBB is not responding. Recovery is
automatic but typically board replacement may be necessary.
A154 (Serial EEPROM Hardware Failure)
The unit will be completely shut down. The serial EEPROM chip
on the MBB which stores the unit's configurations is not respond-
ing. Recovery is automatic but typically board replacement is
necessary.
T155 (Serial EEPROM Storage Failure Error)
Configuration data in the serial EEPROM chip cannot be verified
which may mean MBB replacement. It is possible that a reinitial-
ization of the database or particular storage area(s) may clean up
this problem. Reset is automatic.
A156 (Critical Serial EEPROM Storage Fail Error)
The unit is completely shut down. Critical configuration data in
the serial EEPROM chip cannot be verified which may mean
MBB replacement. Recovery is automatic but typically board re-
placement is necessary.
NOTE: The machine will shut down. This may happen after
downloading via the CCN if the device code was corrupted. Try
downloading again or use the LEN connection to download.
A157 (A/D Hardware Failure)
The unit will be completely shut down. The analog to digital con-
version chip on the MBB has failed. Recovery is automatic but
typically board replacement is necessary.
A169 (Expansion Valve Control Board Comm Failure)
Cooling is disabled until communication with the EXV control
board is re-established. Recovery is automatic. Reason for failure
may be incorrect wiring, power loss to the control board, or dam-
age to the RS-485 drivers on the LEN bus.
T170 (Compressor Expansion Board Comm Failure)
Compressors A3 and B3 are disabled until communication with
the CEB control board is re-established. Recovery is automatic.
Reason for failure may be incorrect wiring, power loss to the con-
trol board, or damage to the RS-485 drivers on the LEN bus.
128
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Table of Contents
Troubleshooting
