Stulz FLAIR series, Installation, Operation And Maintanance Manual

Page: 26 / 48

(©Aug, 2007)
FLAiR Series Installation, Operation & Maintenance Manual
Air Technology Systems, Inc.
2-15
255 psig will close the low fan speed contacts and
reduce the fan speed. Setpoint range is 170 to 400
psig. The differential is non-adjustable and set at 70
psi.
NOTE
This switch and settings does not apply to units
designed for a power supply greater than 277V.
2.8.4.1.3 Variable Condenser Fan Speed
(SCS-SA and OHS RCU-O Models, -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.
Wire the condenser/condensing unit in accordance
with the electrical schematic and appropriate codes.
The fan speed controller will automatically control the
head pressure. On systems with more than one fan
on the condenser, the remaining motors cycle on and
off based on pressure.
2.8.4.1.4 Intelligent Control
(SCS-EC Models only, -20°F)
Used for outdoor installations where ambient con-
denser air inlet temperatures may fall to -20°F, intelli-
gent pressure control is designed to maintain dis-
charge 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
2.8.4.1.5 Flooded Head Pressure Control
(SCS-AA, HES-CAA, OHS RCU-O
and OHS RCU-I Models, -30°F)
Used for outdoor or indoor 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 is used in the
ball” while the unit is running. If the “float ball” is
positioned at the bottom of the sight indicator, addi-
tional refrigerant charge is needed. When the “float
ball” reaches the top of the indicator, the unit is fully
charged.
2.8.3 Low/High Pressure Limit Switch
Air conditioning systems utilizing thermal expansion
valves are equipped with hermetically sealed high-
pressure and low-pressure switches. These switches
are pre-set by the manufacturer and cannot be ad-
justed. 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.
2.8.4 Head Pressure Controls
2.8.4.1 Air-Cooled Systems AR and AHU units)
2.8.4.1.1 Condenser Fan Cycling
(SCS-AA and OHS RCU-O Models, 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 wit
h SPST (Single Pole, Single Throw)
contacts and an automatic reset. The switch activates
the condenser blower contactor when the discharge
pressure reaches 275 psig to maintain the condensing
temperature.
Factory setting: Switch contacts are set to close on a
pressure rise to 275 psig and open at 205 psig.
Setpoint range is 170 to 375 psig. The differential is
non-adjustable and set at 70 psi.
2.8.4.1.2 Condenser Multi-Speed Fan Switch
(HES-CAA and OHS RCU-I Models, 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 pres-
sure 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 at approximately 325 psig and returns the
fan (blower) from high speed to low speed at approxi-
mately 255 psig.
Factory setting: On pressure rise, the high fan speed
contacts are set to close at 325 psig. This will
increase the condenser fan speed. A pressure drop to