Carrier 69NT40-541-505 Operation And Service Manual

T-368 4–12During setpoint pulldown supply air tempera-ture is controlled according to the unit’s nomi-nal supply air setpoint.During CCPC pulldown the supply air tempera-ture is lowered somewhat relative to the nomi-nal setpoint. Evaporator fans are forced tooperate at high speed.Steady−state CCPC control maintains the same loweredsupply air temperature as was used during CCPC pull-down. The compressor cycles on and off according toreturn air high and low limits. Depending on the fan modeof operation selected, the evaporator fans may be pro-grammed to run at low speed some or all of the timeaccording to the control logic.4.6 CONTROLLER ALARMSAlarm display is an independent controller software func-tion. If an operating parameter is outside of expectedrange or a component does not return the correct signalsback to the controller, an alarm is generated. A listing ofthe alarms is provided in Table 4–6.The alarm philosophy balances the protection of therefrigeration unit and that of the refrigerated cargo. Theaction taken when an error is detected always considersthe survival of the cargo. Rechecks are made to confirmthat an error actually exists.Some alarms requiring compressor shutdown have timedelays before and after to try to keep the compressor online. An example is alarm code “LO,” (low main voltage),when a voltage drop of over 25% occurs, an indication isgiven on the display, but the unit will continue to run.An alarm is indicated by flashing an alarm code on thedisplay panel, and for some alarms, by the alarm lightilluminating.When an Alarm Occurs:a. The red alarm light will illuminate for “20 series”alarms.b. If a detectable problem is found to exist, itsalarm code will be alternately displayed with theset point on the left display.c. The user should scroll through the alarm list todetermine what alarms exist or have existed.Alarms must be diagnosed and corrected beforethe Alarm List can be cleared.To Display Alarm Codes:a. While in the Default Display mode, press theALARM LIST key. This accesses the Alarm ListDisplay Mode, which displays any alarmsarchived in the Alarm Queue.b. The alarm queue stores up to 16 alarms in thesequence in which they occurred. The user mayscroll through the list by depressing an ARROWkey.c. The left display will show “AL##,” where ## isthe alarm number sequentially in the queue.d. The right display will show the actual alarmcode. “AA##” will display for an active alarm,where “##” is the alarm code. Or “IA##” will dis-play for an inactive alarm.e. “END” is displayed to indicate the end of thealarm list if any alarms are active.f. “CLEAr” is displayed if all alarms are inactive.The alarm queue may than be cleared by press-ing the ENTER key. The alarm list will clear and“-----” will be displayed.NOTEAL26 is active when all of the sensors arenot responding. Check the connector at theback of the controller, if it is loose orunplugged, reconnect it. Then run a pretriptest (P5) to clear AL26.4.7 PRE−TRIP DIAGNOSTICSPre-trip diagnostics is an independent controller functionthat will suspend normal refrigeration controller activitiesand provide preprogrammed test routines. The test rou-tines include Auto Mode testing, which automatically per-forms a pre−programmed sequence of tests or ManualMode testing, which allows the operator to select and runany of the individual tests.CAUTION!Pre-trip inspection should not be per-formed with critical temperature cargoesin the container.CAUTION!When Pre-Trip key is pressed, dehumidi-fication and bulb mode will be deacti-vated. At the completion of Pre-Tripactivity, dehumidification and bulb modemust be reactivated.Downloaded from ManualsNet.com search engine