Specifications

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Slow Change Override — The control prevents the capacity

stages from being changed when the leaving ﬂuid tempera-

ture is close to the set point (within an adjustable deadband)

and moving towards the set point.

Ramp Loading ( ) — Limits the rate of change of leav-

ing ﬂuid temperature. If the unit is in a cooling mode and

conﬁgured for Ramp Loading, the control makes 2 compari-

sons before deciding to change stages of capacity. The con-

trol calculates a temperature difference between the control

point and leaving ﬂuid temperature. If the difference is greater

than 4° F (2.2° C) and the rate of change (°F or °C per minute)

is less than the conﬁgured Cooling Ramp Loading value

( ), the control does not allow any changes to the

current stage of capacity.

Low Entering Fluid Temperature Unloading — When the

entering ﬂuid temperature is below the control point, the con-

trol will attempt to remove 25% of the current stages being

used. If exactly 25% cannot be removed, the control re-

moves an amount greater than 25%, but no more than nec-

essary. The lowest stage will not be removed.

Low Discharge Superheat — If a circuit’s discharge super-

heat is less than 15° F (8.3° C), the control does not increase

the current capacity stage and the EXD is not opened any

further. If the discharge superheat is less than 10° F

(5.6° C) and decreasing, the EXD is closed 50 steps every

10 seconds. If the discharge superheat is less than

5° F (2.8° C) and decreasing, the circuit is unloaded every

30 seconds until the superheat is greater than 5° F

(2.8° C). The ﬁnal capacity stage is not unloaded unless an

alarm condition exists. This override is ignored for the ﬁrst

3 minutes after a compressor is started.

Low Saturated Suction Temperature — To avoid freezing

the cooler, the control will compare the circuit Saturated Suc-

tion temperature with a predetermined freeze point. For wa-

ter circuits, the freeze point is 28 F (−2.2 C). For brine cir-

cuits, the freeze point is 8° F (4.4° C) below the cooling set

point (lower of 2 cooling set points for dual conﬁguration).

If the saturated suction temperature is below the freeze point,

the unit capacity is not allowed to increase. For brine cir-

cuits, the freeze point can be entered by pressing

and scrolling 12 items down. The control will use the Brine

Freeze Point value less 6°F (3.3°C) as the freeze point to

compare with the Saturated Suction temperature. The de-

fault 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. This

value is adjustable from −15 F to 34 F (−26.1 to 1.1 C). For

water (brine) circuits, if the Saturated Suction temperature

falls below 34 F (1.1 C) (the Brine Freeze Point), the unit

capacity will not increase. If the Saturated Suction tempera-

ture 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 min-

utes, the circuit will shut down.

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 tem-

perature. Conﬁgured maximums are 154 F (67.8 C) for 30GX,

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 tem-

perature, 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 tempera-

ture, and minimum 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 (30GX) or analog water valve (30HXC) to maintain the

saturated condensing temperature to a conﬁgurable set point.

The fans are staged or speed varied (30GX) or water valve

controlled (30HX) based on each circuit’s saturated con-

densing 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 4. Fan stage settings are shown in Table 5.

AIR COOLED UNITS (30GX) — See Fig. 5 for condenser

fan locations.

0 200 400 600 800 1000

TIME (SECONDS)

2 STARTS

3 STARTS

DEADBAND EXAMPLE

LWT (F)

MODIFIED

DEADBAND

STANDARD

DEADBAND

LWT (C)

LEGEND

LWT — Leaving Water

Temperature

Fig. 4 — Deadband Multiplier