Carrier 30GTR Specifications download pdf (Page 56)

Refrigerant Feed Components — Each circuit has

all necessary refrigerant controls.

ELECTRONIC EXPANSION VALVE (EXV) — A cutaway

view of valve is shown in Fig. 28.

High-pressure liquid refrigerant enters valve through bot-

tom. A series of calibrated slots have been machined in side

of oriﬁce assembly.As refrigerant passes through oriﬁce, pres-

sure drops and refrigerant changes to a 2-phase condition

(liquid and vapor). To control refrigerant ﬂow for different

operating conditions, a sleeve moves up and down over ori-

ﬁce and modulates oriﬁce size.Asleeve is moved by a linear

stepper motor. Stepper motor moves in increments and is con-

trolled directly by EXV module. As stepper motor rotates,

motion is transferred into linear movement by lead screw.

Through stepper motor and lead screw, 1500 discrete steps

of motion are obtained. The large number of steps and long

stroke results in very accurate control of refrigerant ﬂow. The

minimum position for operation is 120 steps.

The EXV module controls the valve. The lead compressor

in each circuit has a thermistor located in the suction mani-

fold after the compressor motor and a thermistor located in

a well where the refrigerant enters the cooler. The ther-

mistors measure the temperature of the superheated gas en-

tering the compressor cylinders and the temperature of the

refrigerant entering the cooler. The difference between the

temperature of the superheated gas and the cooler suction

temperature is the superheat. The EXV module controls the

position of the electronic expansion valve stepper motor to

maintain 29 F (16 C) superheat.

The superheat leaving cooler is approximately 3° to 5° F

(2° to 3° C), or less.

Because EXV status is communicated to the Main Base

Board (MBB) and is controlled by the EXV modules (see

Fig. 27), it is possible to track the valve position. By this

means, head pressure is controlled and unit is protected against

loss of charge and a faulty valve. During initial start-up, EXV

is fully closed. After initialization period, valve position is

tracked by the EXV module by constantly monitoring amount

of valve movement.

The EXV is also used to limit cooler saturated suction tem-

perature to 50 F (10 C). This makes it possible for the chiller

to start at higher cooler ﬂuid temperatures without overload-

ing the compressor. This is commonly referred to as MOP

(maximum operating pressure).

If it appears that EXV is not properly controlling circuit

operation to maintain correct superheat, there are a number

of checks that can be made using test functions and initial-

ization features built into the microprocessor control. See Serv-

ice Test section on page 29 to test EXVs.

DIMENSION

FAN TYPE

Standard Low Noise (Optional)

A 0.509 (13 mm) 1.509 (38 mm)

B 0.889 (22 mm) 1.139 (29 mm)

NOTE: Fan rotation is clockwise as viewed from top of unit.

Fig. 26A — Condenser Fan Adjustment —

Standard 50 and 60 Hz Units and

60 Hz Low Noise Fan Option Units

PLASTIC FAN

PROPELLER

CLEARANCE

OF 0.25 INCHES

(6.4 MM)

FAN DECK

SURFACE

FAN ORIFICE

Fig. 26B — Condenser Fan Adjustment —

50 Hz Low Noise Fan Option Units

NOTE: Dimensionsarein millimeters. Dimensions in [ ]arein inches.

Fig. 27 — Condenser Fan Adjustment,

Units with High-Static Fan Option

Fig. 28 — Electronic Expansion Valve (EXV)

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Carrier 30GTR Specifications Page 56

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