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Cooler Freeze Protection
— The control will try to prevent
shutting the chiller down on a Cooler Freeze Protection alarm
by removing stages of capacity. If the cooler fluid selected
is Water, the freeze point is 34 F (1.1 C). If the cooler fluid
selected is Brine, the freeze point is the Brine Freeze Point (Set
Points
FRZ
BR.FZ). This alarm condition (A207) only
references leaving fluid temperature and NOT Brine Freeze
point. If the cooler leaving fluid temperature is less than the
freeze point plus 2.0° F (1.1° C), the control will immediately
remove one stage of capacity. This can be repeated once every
30 seconds.
Low Saturated Suction Protection
— The control will try to
prevent shutting a circuit down due to low saturated suction
conditions by removing stages of capacity. These circuit alert
conditions (T116, T117) compare saturated suction tempera-
ture to the configured Brine Freeze Point (Set
Points
FRZ
BR.FZ). The Brine Freeze point is a user-
configurable value that must be left at 34 F (1.1 C) for 100%
water systems. A lower value may be entered for systems with
brine solutions, but this value should be set according to the
freeze protection level of the brine mixture. Failure to properly
set this brine freeze point value may permanently damage the
brazed plate heat exchanger. The control will initiate Mode 7
(Circuit A) or Mode 8 (Circuit B) to indicate a circuit’s capaci-
ty is limited and that eventually the circuit may shut down.
Head Pressure Control — The main base board
(MBB) controls the condenser fans to maintain the lowest
condensing temperature possible, and thus the highest unit
efficiency. The MBB uses the saturated condensing tempera-
ture input from the discharge pressure transducer and outside
air temperature sensor to control the fans. If OAT is greater
than 70 F before a circuit is starting, then all condenser fan
stages will be energized. A fan stage is increased based on
SCT (saturated condensing temperature). When the highest
SCT is greater than the Fan On Set Point (Set
Points
HEAD
F. ON ), then an additional stage of fan will
be added to the current fan stage. Fan On Set Point (F. O N )
equals Head Set Point (Set Points
HEAD
H.DP) except
after a fan stage increase when the Head Set Point is increased
by Fan Stage Delta (Set Points
HEAD
F. D L T ). A fan
stage is decreased when the SCTs of both circuits are less than
the Fan Off Set Point (Set Points
HEAD
F. O F F ) for
two minutes. Table 20 shows the number of fan stages, contac-
tors energized and the fans that are on during the fan stage.
Unit sizes 035 to 060 have common fan control. Figure 14
shows the location of each fan and compressor within the unit.
MOTORMASTER
®
V OPTION — Motormaster V is stan-
dard on 30RAP010 and 015 size units. For all other units that
need low-ambient operation, the lead fan on a circuit can be
equipped with the Motormaster V head pressure controller op-
tion or accessory. The controller is energized with the first fan
stage and adjusts fan speed to maintain a SCT of 72 F (22.2 C).
The first stage of fan operation is controlled by the Motormas-
ter V controller. Refer to Fig. 15 for condenser fan layout infor-
mation. The Motormaster is configured in the Motormaster Se-
lect (Configuration
MM
MMR.S)
Operation of Machine Based on Control
Method and Cooling Set Point Selection Set-
tings —
Machine On/Off control is determined by the
configuration of the Control Method (Configura-
tion
OPT2
CTRL) and Cooling Set Point Select (Config-
uration
SLCT
CLSP) variables. All units are factory
configured with Cooling Set Point Select set to 0 (single set
point). With the control method set to 0, simply switching the
Enable/Off/Remote Contact switch to the Enable or Remote
Contact position (external contacts closed) will put the chiller
in an occupied state. The control mode (Operating
Modes
MODE) will be 1 (OFF LOCAL) when the switch is
Off and will be 5 (ON LOCAL) when in the Enable position or
Remote Contact position with external contacts closed.
1
60
170
130
140
150
160
110
120
130
80
90
100
50
60
70
30
40
-30 -20 -10 0 10 20 304050607080
SCT (F)
SST (F)
LEGEND
Fig. 14 — Operating Envelope for R-410A Compressor
SCT —
Saturated Condensing Temperature
SST —
Saturated Suction Temperature
a30-4969