Head Pressure Control; Air-Cooled Units (30Gxn,R) - Carrier ComfortLink 6 Series Controls, Start-Up, Operation, Service, And Troubleshooting

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LEGEND
LWT — Leaving Water Temperature
Low Saturated Suction Temperature — To avoid freezing the
cooler, the control will compare the circuit Saturated Suction
temperature with a predetermined freeze point.
For water [brine] circuits, if the Saturated Suction tempera-
ture falls below 34 F (1.1 C) [the Brine Freeze Point], the unit
capacity will not increase. If the Saturated Suction temperature
falls below 28 F (–2.2 C), [the Brine Freeze Point minus 6° F
(3.3° C)], for 90 seconds, all loaders in the circuit are turned
off. If this condition continues for a total of 3 minutes, the cir-
cuit will alarm and shut down.
For Brine applications, the Brine Freeze Point (Configura-
tion Mode, SERV sub-mode, BR.FZ) must be configured for
the freeze point of the brine solution. The control will use the
Brine Freeze Point value minus 6° F (3.3° C) as the point to
compare with the Saturated Suction Temperature. The default
for the Brine Freeze Point is 34 F (1.1 C), which means the
control will use 28 F (–2.2 C) as the freeze point. The Brine
Freeze Point is adjustable from –20 F to 34 F (–29 C to 1.1 C).
Failure to set the Brine Freeze Point correctly will cause
improper unit operation.
High Condensing Temperature Unloading — Every 10 sec-
onds the control checks for the conditions below. Loaders will
be cycled as needed to control the saturated condensing
temperature below the configured maximum condensing
temperature. Configured maximums are 154 F (67.8 C) for
30GXN,R, 152 F (66.7 C) for 30HXA, and 122 F (50 C) for
30HXC units. If a circuit's saturated condensing temperature is
more than 12° F (6.7° C) below the maximum condensing
temperature, the circuit capacity is not allowed to increase. If
the saturated condensing temperature is more than 2° F
(1.1° C) above the maximum condensing temperature for
60 seconds, a loader is turned off. If the saturated condensing
temperature rises to more than 5° F (2.8° C) above the maxi-
mum condensing temperature during the 60 seconds, a loader
is turned off immediately. If all the loaders were already off, the
compressor is shut down and an alarm is generated.
MOP (Maximum Operating Pressure) Override — The con-
trol monitors saturated condensing and suction temperature for
each circuit as well as differential oil pressure. Based on a
configurable maximum operating set point (saturated suction
temperature), set maximum condensing temperature, and mini-
mum differential oil pressure, the control may reduce the
number of capacity stages being used and/or may lower the
EXD position when system pressures approach the set
parameters.

Head Pressure Control

GENERAL — The microprocessor controls the condenser fans
(30GXN,R) to maintain the saturated condensing temperature
to a configurable set point. The 30HXA condenserless units
with a 09DK condenser use a combination of factory-supplied
DEADBAND EXAMPLE
0 200
STANDARD
DEADBAND
Fig. 7 — Deadband Multiplier
400 600
TIME (SECONDS)
fan cycling pressure switches (shipped in the 30HXA control
box), temperature switches, and an accessory Motormaster
control to maintain head pressure independent of 30HXA unit
control. The fans are staged or speed varied (30GXN,R) or
water valve controlled (30HXC) based on each circuit's satu-
rated condensing temperature and compressor status. Water
cooled units (30HXC) operating at less than 70 F (21.1 C) for
entering condenser water require the use of head pressure
control.
The chiller must be field configured for the options shown
in Table 6. Fan stage settings are shown in Table 7.
AIR-COOLED UNITS (30GXN,R) — See Fig. 8 for con-
denser fan locations.
Without Motormaster V Control — The first stage of fans are
turned on based on compressor status or a Head Pressure Set
Point based on Saturated Condensing Temperature (SCT).
Additional fan stages are added when the SCT exceeds the
Head Pressure Set Point. The Head Pressure Set Point is
configurable in the Set Point sub-mode. The default is 113 F
(45 C). Once a fan stage has been added, the software tempo-
rarily modifies the head pressure set point by adding 15° F
(8.3° C) for 35 seconds. A fan stage will be removed when the
Saturated Condensing Temperature has been less than the
Head Pressure Set Point minus 35° F (19.4° C) for 2 minutes.
The control uses the higher of the 2 Saturated Condensing
Temperature values for 30GXN,R080-160 units. For the
30GXN,R153, 163-350 units, each circuit's fan stages are
independently controlled based on the circuit Saturated
Condensing Temperature. Refer to Table 8 for condenser fan
control information. See Fig. 9A for operational information.
With Motormaster V Control — For low-ambient operation,
the lead fan in each circuit can be equipped with the optional or
accessory Motormaster head pressure controller. If factory
installed, the controller will be configured for 4 to 20 mA con-
trol. With the Variable Head Pressure Select option set to 1 (4
to 20 mA), the MBB module calculates the required output
based on Saturated Condensing temperature, Head Pressure set
point, and a PID (proportional integral derivative) loop calcula-
tion. This 4 to 20 mA output is driven through the SCB.
Proportional, Integral, and Derivative gain parameters for
air-cooled controls are adjustable and can be found in the
SERV sub-mode under the Configuration mode. Only certified
Carrier Comfort Network technicians should perform checkout
and adjustment of the PID loop. To obtain this accessory for
field installation, order by part number 30GX-900---071, 072,
073 for a single controller package (30GXN,R080-160). Order
part number 30GX-900---074, 075, 076 for a dual controller
package (30GXN,R153, 163-350). These packages contain all
the hardware required to install this accessory. See Fig. 9B for
operational information.
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2 STARTS
800 1000
3 STARTS
MODIFIED
DEADBAND
®