Carrier GTR040-420 Especificações descarregar pdf (Página 64)

Refrigerant Circuit

LEAK TESTING — Units are shipped with complete operat-

ing charge of refrigerant R-22 for 30GTN,R and R-134a for

30GUN,R (see Physical Data tables supplied in the chiller’s

installation instructions) and should be under sufficient pres-

sure to conduct a leak test. If there is no pressure in the system,

introduce enough nitrogen to search for the leak. Repair the

leak using good refrigeration practices. After leaks are

repaired, system must be evacuated and dehydrated.

REFRIGERANT CHARGE (Refer to Physical Data tables

supplied in the chiller’s installation instructions) — Immedi-

ately ahead of filter drier in each circuit is a factory-installed

liquid line service valve. Each valve has a

-in. Schrader con-

nection for charging liquid refrigerant.

Charging with Unit Off and Evacuated

— Close liquid line

service valve before charging. Weigh in charge shown on unit

nameplate (also in Physical Data tables supplied in the chiller’s

installation instructions). Open liquid line service valve; start

unit and allow it to run several minutes fully loaded. Check for

a clear sight glass. Be sure clear condition is liquid and not

vapor.

Charging with Unit Running

— If charge is to be added while

unit is operating, all condenser fans and compressors must be

operating. It may be necessary to block condenser coils at low

ambient temperatures to raise condensing pressure to approxi-

mately 280 psig (1931 kPa) to turn all condenser fans on. Do

not totally block a coil to do this. Partially block all coils in uni-

form pattern. Charge each circuit until sight glass shows clear

liquid, then weigh in amount over a clear sight glass as listed

in Physical data tables supplied in chiller’s installation

instructions.

Thermistors —

Electronic control uses 4 to 10 ther-

mistors to sense temperatures used to control the operation of

chiller.

Thermistors T1-T9 vary in their temperature vs resistance

and voltage drop performance. Thermistor T10 is a 10 kΩ in-

put channel and has a different set of temperature vs resistance

and voltage drop performance. Resistances at various tempera-

tures are listed in Tables 34A-35B.

LOCATION — General locations of thermistor sensors are

shown in Fig. 7-10. See Table 2 for pin connection points.

REPLACING THERMISTOR T2

1. Remove and discard original sensor and coupling. Do

not disassemble new coupling. Install assembly as

received. See Fig. 36.

2. Apply pipe sealant to

-in. NPT threads on replacement

coupling, and install in place of original. Do not use the

packing nut to tighten coupling. Damage to ferrules will

result.

3. Thermistor T2 (entering fluid temperature) should not be

touching an internal refrigerant tube, but should be close

enough to sense a freeze condition. Recommended dis-

tance is

in. (3.2 mm) from cooler tube. Tighten pack-

ing nut finger tight to position ferrules, then tighten 1

turns more using a back-up wrench. Ferrules are now at-

tached to the sensor, which can be withdrawn from cou-

pling for service.

REPLACING THERMISTORS T1, T5, T6, T7, AND

T8 — Add a small amount of thermal conductive grease to

thermistor well. Thermistors are friction-fit thermistors, which

must be slipped into wells located in the cooler leaving fluid

nozzle for T1, in the cooler head for T5 and T6 (EXV units

only), and in the compressor pump end for T7 and T8 (EXV

units only).

THERMISTORS T3 AND T4 — These thermistors are

located on header end of condenser coil. They are clamped on

a return bend.

THERMISTOR/TEMPERATURE SENSOR CHECK — A

high quality digital volt-ohmmeter is required to perform this

check.

1. Connect the digital voltmeter across the appropriate

thermistor terminals at the J8 terminal strip on the Main

Base Board for thermistors T1-T6, T9, T10; or the J5

terminal strip on the EXV Board for thermistors T7 and

T8 (see Fig. 37). Using the voltage reading obtained,

read the sensor temperature from Tables 34A-35B. To

check thermistor accuracy, measure temperature at

probe location with an accurate thermocouple-type tem-

perature measuring instrument. Insulate thermocouple

to avoid ambient temperatures from influencing read-

ing. Temperature measured by thermocouple and tem-

perature determined from thermistor voltage reading

should be close, ± 5° F (3° C) if care was taken in apply-

ing thermocouple and taking readings.

2. If a more accurate check is required, unit must be shut

down and thermistor removed and checked at a known

temperature (freezing point or boiling point of water) us-

ing either voltage drop measured across thermistor at the

J8 or J5 terminals, by determining the resistance with

chiller shut down and thermistor disconnected from J8 or

J5. Compare the values determined with the value read by

the control in the Temperatures mode using the Marquee

display.

IMPORTANT: When adjusting refrigerant charge, circu-

late fluid through cooler continuously to prevent freezing

and possible damage to the cooler. Do not overcharge, and

never charge liquid into low-pressure side of system.

Sensor T2 is installed directly in the fluid circuit. Relieve

all pressure or drain fluid before removing.

FLUID-SIDE TEMPERATURE SENSOR (T1) AND

REFRIGERANT TEMPERATURE SENSOR (T5, T6, T7, T8)

FLUID-SIDE TEMPERATURE SENSOR (T2)

NOTE: Dimensions in ( ) are in millimeters.

Fig. 36 — Thermistors (Temperature Sensors)

X = T1,T5,T6 = 3

″

(76)

T7,T8 = 4

″

(102)

1 2 ... 59 60 61 62 63 64 65 66 67 68 69 ... 103 104

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