Troubleshooting guide

MAGNUM VERSION 8 MANUAL REVISION 3.1
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Refrigerant Level Control 7.43.5.
There is an alternate method to control the EXV based on Ref Level
7.43.5.1. Minimum Refrigerant Level target (HVAC ONLY)
If active and the EXV is controlled by Refrigerant Level, then a new variable level target logic will be activated. As the
unit capacity increases, the refrigerant level target will change according to a linear calculation between Setpoint #9
“LEVEL TARGET” (the maximum target level) and Setpoint #217 “LOW EXV TARGET” (the minimum target level).
This relationship is explained in the following graph:
EXV control methods for Step Loading Compressors 7.43.6.
Percentage per Step: (Requires Magnum Software HVAC 8.03L and MCS-Config 8.00W or higher)
To control the EXV based on a percentage per step for fixed step compressors, insert the relative load and unload
adjustment percentages in the respective fields in the Relay Output screen. The load and unload adjustments will
increase or decrease respectively based on a percentage of the current EXV position (not a fixed value)
Here is an example of a Hanbell Screw compressor configured to load by fixed steps:
The logic will work as follows: When the compressor starts the EXV will go to the value in the ‘EXV Start (when lead)’
column, in this example it is 25%. The EXV will then modulate normally according to the controlling superheat or
refrigerant level, until the unit is ready to load another step of capacity. Assume the EXV has stayed at 35% when the
second step of capacity is ready to engage (turning off the Hot Gas Bypass). The EXV adjustment will be 50% (the
amount in the ‘EXV Load Adjust’ column of the current EXV position
‘EXV Load Adjust’ column (50%) × current EXV position (35%) = EXV adjustment (17.5%)
20%
25%
30%
35%
40%
45%
50%
25% 80% 135% 190% 245% 300%
EXVLevelTarget
EXVLevel
Target
(Number of steps
(3) × Setpoint #30
"MAX FLA %")
Setpoint #31
"MIN FLA%"
Total Cooling Capacity of Unit
(Example of a 3 step system)
Setpoint #9
“LEVEL TARGET”
Setpoint #217
“LOW EXV TARGET”
These columns are used
for the compressor when
there are multiple
compressors on a single
suction circuit, however,
values must be in these
fields for this logic to be
in effect.