IM 991-2 • MAVERICK II ROOFTOP 62 www.DaikinApplied.com
Unit Options
Optional Low Ambient Compressor Operation
Daikin’s head pressure control operates in conjunction with
Speedtrol by modulating the motor speed of the last condenser
fan of each refrigeration circuit in response to condenser
pressure. By varying the speed of the last condenser fan of
each refrigeration circuit, the VFD option allows mechanical
cooling operation in ambient temperatures down to 0°F
(-18°C). The VFD option senses refrigerant head pressure and
varies the fan speed accordingly. When the pressure rises, the
Speedtrol increases the fan speed; when the pressure falls,
Speedtrol decreases the fan speed.
The VFD throttling range is 250 to 400 psig, fixed. The VFD
fan motor is a three-phase motor, identical to the unit voltage
(208 V to 575 V) and is controlled by a variable frequency drive
(
). The variable frequency drive receives a signal
from a pressure transducer and varies the condenser fan
speed accordingly.
The pressure transducer is calibrated to provide a 1.0 to
5.0V(dc) signal with a 8 to 30 V (dc) input, starting at 1.0 V
(dc) @ 250 psig and up to 5.0 V (dc) @ 400 psig. In order
to maintainan acceptable condensing pressure, the VFD will
modulate the motor down to a minimum of 23Hz, and will not
allow operation below this frequency level. At, or above 400
psig, the VFD will operate the motor at 60 Hz. The control
band between the two frequencies (23 Hz and 60 Hz) is a
linear relationship with the condensing pressure as shown in
(
).
The VFDs and pressure transducers are located in the control
box mounted in the condensing section. Each refrigerant circuit
is independent and has its own respective VFD and pressure
transducer. The Speedtrol option operates independently of the
main unit controller.
Figure 58: R-410A Speedtrol
Figure 59: Speedtrol Operating Characteristics
F11C
F11B
F11A
L1
L2
L3
L1
L2
L3
T1
T2
T3
V1A OC
P24
F
Variable
Frequency
Drive
Pressure
Transducer
Mtr
R11
AFD11
Cndr Mtr #11
eti
h
W
kc
al
B
de
R
PB
yc
ne
uq
er
F
60 Hz
23 Hz
250 psig
(83°)
400 psig
(116°)
Condensing Pressure
