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APPENDIX G — OPTIONAL GREENSPEED/LOW AMBIENT CONTROL (cont)
Configure Greenspeed/Low Ambient Control
The Greenspeed/low ambient control is configured for propor-
tional integral (PI) control mode. The VFDs control varies the
condenser fan motor speed to maintain a setpoint of discharg-
ing head pressure.
The following ComfortLink control configurations must be set
when using a Greenspeed/low ambient device:
• Configuration
COOL
OV.EN = YES
Test Greenspeed/Low Ambient Control
To test the control and motor in the test mode, run compressor
no. 1. The Greenspeed/low ambient electronic control adjusts
the fan speed based on the discharge line pressure input. En-
sure that fans are rotating clockwise (as viewed from above). If
rotation is backward, lock out all power then swap 2 leads AF-
TER the VFDs control.
For A series units, fan stages react to discharge pressure trans-
ducers (DPT) (Pressures
REF.P
DP.A and DP.B) which
are connected to the compressor discharge piping in circuit A
and B. The control converts the pressures to the corresponding
saturated condensing temperatures (Temperatures
REF.T
SCT.A and SCT.B).
Unit size (Configuration
UNIT
SIZE), refrigerant type
(Configuration
UNIT
RFG.T), and condenser heat ex-
changer type (Configuration
UNIT
CND.T) are used to
determine if the second stage fans are configured to respond to
a particular refrigerant circuit (independent control) or both re-
frigerant circuits (common control). The 48/50A060 units with
microchannel (MCHX) condenser heat exchangers are the only
units that utilize independent fan controls.
There are configurations provided for head pressure and low
ambient control that can be found at the local display under
Configuration
COOL.
Greenspeed/Low Ambient (OV)
[OUTDOOR_VFD] The condenser fan staging control for the
unit will be managed directly by the ComfortLink controls
through the use of VFDs. There will be no VFDs installed in
the standard unit. This configuration must be set to YES if the
optional condenser fan VFDs are installed on the unit. Setting
this configuration to YES alters the condenser fan staging se-
quence to accommodate the Greenspeed/low ambient control
algorithm.
The standard unit is capable of mechanical cooling operation
down to 32°F outdoor temperature. With the addition of optional
Greenspeed/low ambient speed control on the stage 1 condenser
fans, mechanical cooling operation down to –20°F outdoor tem-
perature is possible.
This configuration will have a range of NO/YES and will de-
fault to NO.
Head Pressure Setpoint (HPSP)
[HPSP] This is the head pressure setpoint used by the Com-
fortLink control during condenser fan, head pressure control.
This configuration will have a range of 80 to 150°F and a de-
fault of 100°F.
Compressor Lockout Temperature (MC.LO)
[OATLCOMP] This configuration defines the outdoor air tem-
perature below which mechanical cooling is locked out. To
make proper use of Motormaster control, it will be necessary
for an operator to manually change this setting. This configura-
tion will have a range of –20 to 55°F and a default of 40°F.
Fig. T — Greenspeed/Low Ambient VFD Control Location — 48/50A060 Units
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