Troubleshooting guide

MAGNUM VERSION 8 MANUAL REVISION 3.1
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7.35. Vi Port Control Logic (Open Drive Screw only)
The internal volume (Vi) of the open drive screw can be dynamically adjusted to achieve maximum
efficiency modulating the Vi control solenoids. The duration of each solenoid pulse is contained in Setpoint
#114 “Vi PULSE”.
The ratio of discharge pressure divided by suction pressure is calculated. This ratio is blocked between 50
and 22. The value of Setpoint #115 ”Vi DEADBAND” is added to and subtracted from this ratio to develop
a control zone. The control zone will be recalculated based upon the time in Setpoint #116 ”Vi DELAY”.
Refer to Setpoints #117, #118 and #119. The system will pulse the solenoids to keep the Vi reading within
the calculated control zone.
7.36. Operating Schedules
Two operating schedules per each day of the week and 8 holidays are supported by the Magnum
software. Each schedule contains a start and end time. If the time and day of the Magnum clock is within
these limits then the schedule is true and the system will be allowed to run. If not, the system will be off
due to schedule.
7.37. Mod-Motor Limit Control for Flooded Chiller
This option was added for Dunham-Bush flooded chillers. The Mod-Motor is a self-contained device that
modulates a flooded chiller barrel level control valve based on a level sensor. The Magnum controls two
Relay Outputs that change the limits on the movement of the Mod-Motor (The Relay Outputs change
resistance to an input on the Mod-Motor). These Relay Outputs must be placed consecutively and
specified in the General Information panel under the MAG V8 screen of MCS-Config.
 When one or less compressors are on, the first Mod-Motor Relay Output is turned on and the second
Mod-Motor Relay Output is off.
 When 2 or more compressors are on, the first Mod-Motor Relay Output is turned off.
 The second Mod-Motor Relay Output will be turned on if the suction pressure is greater than 85.0 psi
(5.8 bar) and the discharge suction pressure differential is less than 30.0 psi (2.0 bar), and the second
Mod-Motor Relay Output will stay on as long as the suction pressure is greater than 80.0 psi (5.8 bar)
and the discharge suction pressure differential is less than 35.0 psi (2.4 bar). If neither of the above is
true, then the second Mod-Motor Relay Output will be turned off.
7.38. Hot Gas Reheat (Humidity) Control
The Hot Gas Reheat Control option is activated by selecting Yes in the ‘HGReheat’ cell in the
Circuit Base Screen.
The hot gas control sensor is specified in the Evaporator Information panel of the MAG V8
screen. Select the input sensor that will be used to control the hot gas reheat function in the
‘Reheat Control’ cell.