CyberOne EC DX IOM Manual
R407C Pressure Switch Settings:
The high-pressure switch opens at 410 psig and has a manual
reset. The low-pressure switch opens at 10 psig (±4) and
closes at 32 psig (± 5) and has an automatic reset.
2.9.2
Head Pressure Controls-Air
Cooled Systems
2.9.2.1
Condenser Fan Cycling (Condenser
Model SCS-AA, 0 °F )
Used for outdoor installations where ambient condenser air
inlet temperatures are 0 °F or higher, this method utilizes a
high-pressure differential control switch with SPST (Single
Pole, Single Throw) contacts and an automatic reset. The
switch activates the condenser blower contactor when
the discharge pressure reaches a pre-determined value to
maintain the condensing temperature.
R407C Refrigerant
Factory setting: The fan cycling switch contacts are set to
close on a pressure rise to 320 psig and open at 250 psig.
Set point range is 170 to 375 psig. The differential is set at
70 psi and is adjustable.
2.9.2.2
Condenser Multi-Speed Fan
Switch (Model HES-CAA , 0 °F )
Used for indoor installations where ambient condenser air
inlet temperatures are 0 °F or higher, the condenser fan speed
switch senses refrigerant discharge pressure and changes
the condenser blower speed to maintain proper condenser
pressures.
The condenser fan speed switch changes the fan (blower)
from low to high speed when pressure rises and returns the
fan (blower) from high speed to low speed when the pressure
lowers.
R407C Refrigerant:
Factory setting: On pressure rise,
the high fan speed contacts close at 320 psig, increasing
the condenser fan speed. A pressure drop to 250 psig
will close the low fan speed contacts, reducing the fan
speed. The set point range is 170 to 400 psig. The
differential is set at 70 psi and is adjustable.
NOTE
This switch and settings do not apply to units designed
for a power supply greater than 277V.
2.9.2.3
Variable Condenser Fan Speed
(Condenser Model SCS-SA, -20 °F)
Used for outdoor installations where ambient
temperatures may fall to -20 °F, a variable speed condenser
motor control is used to maintain head pressure. The
variable speed motor is located closest to the header end
of the condenser. The fan speed control is a continual
modulation of the motor’s speed. The controller is factory
installed in the outdoor condenser/condensing unit. The fan
speed controller requires no adjustment.
The fan speed controller will automatically control the head
pressure at a level to maintain design refrigerant discharge
pressures. On systems with more than one fan on the
condenser, the remaining motors cycle on and off based on
pressure.
2.9.2.4
Intelligent Control (Condenser
Model SCS-EC only, -20 °F)
Used for outdoor installations where ambient condenser air
inlet temperatures may fall to -20 °F, intelligent pressure
control is designed to maintain discharge pressure by
constantly modulating condenser fan speed. SCS outdoor
condensers are equipped with highly efficient, electronically
commutated (EC), axial fan(s). The EC fan speed is infinitely
variable up to full speed. The control system utilizes
refrigerant pressure transducer(s) to monitor refrigerant
discharge pressure and control the EC fan(s) to the precise
speed needed to maintain design refrigerant discharge
pressures.
2.9.2.5
Flooded Head Pressure Control
(Condenser Model SCS-AA with Fan
Cycling, -30 °F)
Used for outdoor installations where ambient condenser air
inlet temperatures may fall to -30 °F, flooded head pressure
control is designed to maintain head pressure during low
ambient conditions. A head pressure control valve and a
receiver are used in the refrigeration circuit to back up liquid
refrigerant into the condenser coil. The head pressure control
valve is a 3-way modulating valve controlled by discharge
pressure.
When the A/C unit begins to operate, the discharge pressure
rises to (approximately 320 psig for R407C) and the
condenser fan is cycled on, as described in Section 2.9.1.
When ambient temperature drops, the discharge pressure
drops also. When the discharge pressure drops, the head
pressure control valve diverts discharge gas away from the
condenser to the receiver. Liquid flow from the condenser is
restricted, causing liquid to back up in the condenser.
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