Unit controls and safety devices – Carrier 380B User Manual

Page 12

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220

(1517)

PSIG
(kPa)

(469)

(496)

(524)

(552)

(579)

PRESSURE AT SUCTION SERVICE VALVE

Fig. 16 — 38QB042 with 40QB042

or 28HQ,VQ048

Cooling Cycle Operation Check Chart

Fig. 17 — 38QB042 with 40QB042

or 28HQ.VQ048

Heating Cycle Operation Check Chart

Filter Drier

— Install field-supplied filter drier

(Table 3) in system liquid line when refrigerant

system is opened for service as described under

Compressor Removal. Position drier in liquid line

at convenient location.

Pumpdown Procedure

— The system may be

pumped down in order to make repairs on low side

without losing complete refrigerant charge.

1. Attach pressure gage to suction service valve

gage port.

2. Frontseat the liquid line valve.

3. Start unit and run until suction pressure reaches

5 psig (35 kPa) (see Caution).

4. Shut unit off and frontseat suction valve.

5. Vent remaining pressure to atmosphere.

Unit Controls and Safety Devices

HIGH-PRESSURE RELIEF VALVE is located in

compressor. Relief valve opens at a pressure differ

ential of approximately 500 psig (3448 kPa) between

suction (low side) and discharge (high side) to allow

pressure equalization.

INTERNAL CURRENT AND TEMPERATURE

SENSITIVE OVERLOAD resets automatically

when internal compressor motor temperature drops

to a safe level (overloads may require up to 45

minutes to reset). When an internal overload is

suspected of being open, check by using an ohm-

meter or continuity tester. If necessary, refer to

Carrier Standard Service Techniques Manual,

Chapter 2, for complete instructions.

LIQUID LINE LOW-PRESSURE SWITCH

(LLPS) is connected in liquid line to work with

compressor internal thermostat in providing loss-of-

charge protection during the heating cycle. Control

is mounted on liquid line.

With a high-side leak, pressure gradually de

creases until low-pressure control stops the com

pressor. (Low-pressure control settings are shown

in Tables.)

Table 8 — Pressure Switch Settings

UNIT

LIQUID LINE

LOW-PRESSURE SWITCH

Cut-in

Cutout

018
024
030
036

22 ± 5 psig

7 ± 3psig

042