McQuay AGS 225D, Operating Manual

Page: 49 / 82

OM AGSD-1 49
T2 – Transition from Pressure Control to Superheat Control requires all of the following
•
Suction Superheat >= Superheat target
•
Evap LWT <= 60 F
•
EXV State = Pressure AND Discharge Superheat >= 22 F for at least 3 minutes
•
Discharge Temperature <= 180 F
•
Low Evap Pressure Unload event not active
T3 – Transition from Superheat Control to Pressure Control requires any of the following
•
Evap LWT > 63 F
•
Low Evap Pressure Unload event active
•
Discharge Superheat < 22 F
•
Discharge Temperature > 185 F
T4, T5 – Transition from any state to Closed state requires the following
•
Compressor State not Run
EXV Control Range
The table below shows the EXV range for each size compressor at minimum and maximum
capacity. The minimum and maximum values vary linearly with slide position, defining a
new EXV control range for every change in slide position.
Compressor Size
EXV Slide %
5mm
220mm 235mm
Min 0
Min EXV Pos
Setpoint
Min EXV Pos
Setpoint
Min EXV Pos
Setpoint
Max 0 3000 3000 3000
Min 100 870 1080 1300
Max 100 3400 4200 5000
Based on the values in the above table, the EXV control range varies as shown in the table
below. The shaded area the control range.
Max EXV
@ 100%
100
Max EXV
@ 0%
Min EXV
@ 0%
EXV Control Range
0
Slide Position Target (%)
EXV
Steps
Min EXV
@ 100%
Manual EXV Control
The EXV position can be set manually. Manual control can only be selected when the
compressor is in the run state. At any other time, the EXV control setpoint is forced to auto.