Sterling 30RA010-055 Compressor and Unit Protective Devices, Check Unit Safeties, Switch Fixed

TXV SENSOR

LOCATION

TXV SENSOR

LOCATION

Fig. 34 — Mounting Locations for TXV Sensing Bulb

The amount of capacity reduction achieved by the mini- mum load valve is not adjustable. The total unit capacity with the minimum load valve is shown in Table 7.

PRESSURE RELIEF DEVICES — All units have one pres- sure relief device per circuit located in the liquid line which re- lieves at 210 F (100 C).

Compressor and Unit Protective Devices

MANUAL STARTER — There is one manual starter per compressor in each unit. It protects the compressor(s) against overloading, locked rotor conditions, and primary single phas- ing. If the manual starter trips, determine the cause and correct it before resetting.

Manual starters are factory set; field adjustment should not be required. Manual starters are also factory installed for each condenser fan motor and factory-installed chilled water pump.

NOTE: Two-speed condenser fan motors on sizes 010-018 and 032-040 have manual starters so that the motor is protected while running in both low and high speed modes. Refer to Appendix B for factory settings.

COMPRESSOR INTERNAL THERMAL PROTECTION — All models include internal compressor protection. Models using the SM110 compressor (015 50 Hz and 018 60 Hz) have internal line break overloads. All other compressor models have internal discharge temperature thermostats that are wired in series with the compressor high pressure switch in the com- pressor motor junction box. The thermostat opens and shuts off the compressor if the discharge gas temperature exceeds 275 F (135 C). The thermostat will automatically reset when the tem- perature drops below a preset level, however, the control mod- ule will keep the unit locked off until the alert condition is reset.

Check Unit Safeties

HIGH-PRESSURE SWITCH — A high-pressure switch is provided to protect each compressor and refrigeration system from unsafe high pressure conditions. See Table 32 for high- pressure switch settings.

The high-pressure switch is mounted in the discharge side of each compressor. A snubber is provided between the com- pressor discharge manifold and the high-pressure switch to pre- vent pressure pulsations from damaging the switch.

The high-pressure switch is mounted in the discharge line of each compressor. If an unsafe, high-pressure condition should exist, the switch opens and shuts off the affected compressor. The compressor feedback signal to J9 of the MBB then opens causing an alert condition. The MBB prevents the compressor from restarting until the alert condition is reset. The switch should open at the pressure corresponding to the appropriate switch setting as shown in Table 32.

Table 32 — Factory Settings, High-Pressure

Switch (Fixed)

UNIT	CUTOUT		CUT-IN
	Psig	kPa	Psig	kPa
30RA	426 ± 7	2937 ± 48	324 ± 20	2206 ± 138

Clear the alarm using the Scrolling Marquee display as de- scribed on page 42. The unit should restart after the compressor anti-short-cycle delay, built into the unit control module, expires.

PRESSURE TRANSDUCERS — Each refrigerant circuit is equipped with a suction and discharge pressure transducer. The transducers are NOT the same part number. The discharge pressure transducer is the universal pressure transducer while the suction pressure transducer is a discrete low pressure trans- ducer. These inputs to the MBB are not only used to monitor the status of the unit, but to also maintain operation of the chill- er within the compressor manufacturer's specified limits. The input to the MBB from the suction pressure transducer is also used to protect the compressor from operating at low pressure conditions. In some cases, the unit may not be able to run at full capacity. The control module will automatically reduce the ca- pacity of a circuit as needed to maintain specified maximum/ minimum operating pressures.

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