Troubleshooting guide
MAGNUM VERSION 8 MANUAL REVISION 3.1
48
to be unloaded or if the discharge temperature has returned to normal after the time in Setpoint #101
“SAFETY HOLD DELAY” has passed.
For variable step compressors: The Magnum will begin unloading the compressor(s) with high
discharge temperature until the temperature drops below the calculated value. During this time the
circuit state is HI DISC UNLOAD. Once this temperature has been reached, the circuit state will be HI
DISC HOLD. The compressor will remain in that state until the capacity control indicates that less
capacity is needed or if the discharge temperature has returned to normal after the time in Setpoint
#101 “SAFETY HOLD DELAY” has passed.
Normal pressure is defined as any value less than the calculated value of Setpoint #87 “HI DISC TMP”
minus Setpoint #89 “HI DISC RELD”. Refer to Setpoints #88 and #89 for additional information.
7.26. High Ampere Unloading and Holding
This option is activated when the Setpoint #75 “HI AMPS %” is active. Note: This option can only be active
for fixed step compressors. When the amp draw is within one-half of the calculated HI AMP safety value,
the Magnum will turn on the WARNING Relay Output if specified in MCS-Config and take the following
action:
For fixed step compressors: the Magnum will turn off one step of capacity associated with that
compressor until that compressor is in an UNLOADED state that is all steps except one are
unloaded. The circuit state will be HI AMP HOLD. The compressor will remain in that state until the
capacity control indicates that another step is to be unloaded or if the amp draw has returned to
normal after the time in Setpoint #101 “SAFETY HOLD DELAY” has passed.
7.27. Low Water Temperature Unloading and Holding
When the leaving liquid temperature is within 1.5° F (.8° C) of the freeze safety, the Magnum will turn on
the WARNING Relay Output if specified in MCS-Config and take the following action:
For fixed step compressors: The Magnum will turn off one step of capacity of the compressor(s) with
low water temperature until all steps except one are unloaded. The circuit state will be LO TMP
HOLD. The compressor will remain in that state until the capacity control indicates that another step is
to be unloaded or if after 5 minutes the leaving liquid temperature has turned to normal.
For variable step compressors: The Magnum will begin unloading the compressor(s) with low water
temperature until the leaving liquid temperature rises above the calculated value. During this time the
circuit state is LO TMP UNLOAD. Once the leaving liquid temperature rises above the calculated
temperature the circuit state will change to LO TMP HOLD. The compressor will remain in that state
until the capacity control indicates that less capacity is needed or if after 5 minutes the leaving liquid
temperature has turned to normal.
Normal leaving liquid temperature is defined as any value more than 3.0F (1.6C) above the freeze safety
trip value.
7.28. Energy Efficient Compressor Staging
In a multi-screw system, it may be more efficient to run the screws at less than 100% capacity until all
compressors have been turned on.
The following Setpoints are used to control the screw compressor staging:
Setpoint #30 “MAX SLIDE %” contains the maximum slide percentage, based upon amp draw, before
the system will bring on the next compressor.
Setpoint #31 “MIN SLIDE %” contains the minimum slide percentage, based upon amp draw, before
the system will reduce the number of compressors wanted on.
For example if “MAX SLIDE %” is 80% and the “MIN SLIDE %“ is 40%, the two-screw compressor
system would be ramped up as follows:
The Lead compressor will be started at 40% and increased up to 80%. If more capacity is needed the
next compressor will be started at 40% and the first compressor decreased to 40%. The two
compressors will then have their slide positions changed together. Since there are only two
compressors, they will be ramped together up to 100% if required. If both compressors are at 40%
and less capacity is needed, one compressor will be turned off and the other increased to 80%.