48/50PD
Loadshed Group Number (S.GRP)
This corresponds to the loadshed supervisory devices that reside elsewhere on the CCN network and broadcast loadshed and redline commands to its associated equipment parts. This variable will default to zero which is an invalid group number. This allows the loadshed function to be disabled until configured.
Redline Max Capacity (R.MXC)
This configuration tells the unit the maximum cooling/dehumidification capacity allowed active during a loadshed condition.
Redline Max Heat Stages (R.MXH)
This configuration tells the unit the maximum heating stages allowed to be on during a redline condition.
Loadshed Max Heat Stages (R.MXH
This configuration tells the unit the maximum heating stages allowed to be on during a loadshed condition.
The two Demand Limiting methods can be active simultaneously. The lowest cool capacity and heat stage limits imposed by either method are applied, and these “effective limits” are shown in the points CAPLIMIT (Run Status→COOL→LMT.C) and HSTGLIMT (Run Status→HEAT→LMT.H), respectively. In normal running mode, these limits will prevent capacity/stages from being added, or capacity/stages to be removed, as applicable. In test mode, these limits are ignored, and the user may continue to operate at full load.
The point MODEDMDL (Run Status→MODE→D.LMT) is used to show if any Demand Limiting is in effect that prevents the unit from operating either cooling or heating at
IMPORTANT: MODEDMDL may reflect that staging is NOT limited even though Loadshed is active or the network points are being forced, if the capacity/stage limits in effect are not less than the capacity/stages present in the unit.
If a more drastic mode of Demand Limiting is required, the network point HVACDOWN (Run Status→MODE→HV.DN) can be used to prohibit the unit from selecting any HVAC mode, thus preventing the operation of the supply fan, compressors, condenser fans, and heat stages. This point must also be forced, and is reset automatically when not forced, and at POR.
Alarm Handling
There are a variety of different alerts and alarms in the system. Alerts are indicated by TXXX (where XXX is the alert number) on the display and generally signify that the improperly functioning circuit can restart without human interaction. If an alarm occurs, indicated by AXXX (where XXX is the alarm number), the damaged circuit will generally not restart without an alarm reset via the Scrolling Marquee display or CCN.
The response of the control system to various alerts and alarms depends on the seriousness of the particular alert or alarm. In the mildest case, an alert does not affect the operation of the unit in any manner. An alert can also cause a “strike.” A “striking” alert will cause the circuit to shut down for 15 minutes. This feature reduces the likelihood of false alarms causing a properly working system to be shut down incorrectly. If three strikes occur before the circuit has an opportunity to show that it can function properly, the circuit will strike out, causing the shutdown alarm for that particular circuit. Once activated, the shutdown alarm can only be cleared via an alarm reset.
However, circuits with strikes will be given an opportunity to reset their strike counter to zero. As discussed above, a strike typically causes the circuit to shut down. Fifteen minutes later, that circuit will once again be allowed to run. If the circuit is able to run for 1 minute, its replacement circuit will be allowed to shut down (if not required to run to satisfy requested stages). However, the “troubled” circuit must run continuously for a user defined time (Configuration→COOL→RST.C) with no detectable problems
before the strike counter will be reset to zero. Default value is 5 minutes.
CCN Alarm Broadcast
Operators of CCN networks might not want to be notified of “striking” alerts for refrigerant circuits until the circuit has been shut down due to 3 strikes. Set the cooling configuration of Alert Each Strike (Configuration→COOL→ALM.N on display, ALM_NOW on CCN) to YES to broadcast each circuit strike alert. Set Alert Each Strike to NO to broadcast only circuit shut down. Alert Each Strike configuration is ignored during Service Test and all alerts are broadcast.
Alarm Relay Output
The alarm relay output is a normally open 24 vac output between field connection terminal board terminals C and X. Selection of which alerts and alarms will result in closing of the alarm relay may be set in the Alarm Relay Configuration (Configuration→ALM.O). Setting a configuration to YES will result in the alarm output relay, ALRM, status of ON and 24 vac between C and X when that particular condition is in an alarm state. Setting a configuration to NO will result in no action by the alarm output relay for that particular condition.
IMPORTANT: An accessory filter switch can be used along with the alarm relay output function to indicate dirty filter service need.
See the Troubleshooting section for more information on viewing, diagnosing, and clearing alerts and alarms.
TROUBLESHOOTING
The Scrolling Marquee display shows the actual operating conditions of the unit while it is running. If there are alarms or there have been alarms, they will be displayed in either the current alarm list or the history alarm list. (See Table 8.) The Service Test mode allows proper operation of the compressors, fans, and other components to be checked while the unit is not operating. See Service Test.
Complete Unit Stoppage
There are several conditions that can cause the unit not to provide heating or cooling:
SIf an alarm is active which causes the unit to shut down, diagnose the problem using the information provided in Alarms
and Alerts section below.
SCooling and heating loads are satisfied. S Programmed occupancy schedule.
S General power failure.
S Tripped CB1 or CB2
S If
S If
Restart Procedure
Before attempting to restart the machine, check the alarm list to determine the cause of the shut down. If the shutdown alarm for a particular control function has occurred, determine and correct the cause before allowing the unit to run under its own control again. When there is problem, the unit should be diagnosed in Service Test mode. The alarms must be reset before the control function can operate in either Normal mode or Service Test mode.
Control Module Communication
Red LED
Proper operation of the MBB, ECB and AUX1 control boards can be visually checked by looking at the red status LEDs. When operating correctly, the red status LEDs should blink in unison at a rate of once every 2 seconds. If the red LED on the ECB and
24
