Carrier 19XB Controls and Components, Operation, High Condition Pressure Switch Settings

CONTROLS AND COMPONENTS

Figure 1 shows the major components of the PPS system.

Pumpout Unit Ð The pumpout unit consists of a spring- mounted direct motor-driven reciprocating compressor, a water- cooled refrigerant condenser, an oil separator, suction and discharge valves to control refrigerant ¯ow, and prewired safety and control devices. The pumpout unit comes equipped with a 4-way transfer valve manifold to interconnect both liquid and vapor transfer and to pressurize the chiller during trans- fer of refrigerant from chiller to storage tank.

CONTROLS Ð The pumpout unit has the following con- trols: an on/off switch, a 3-amp fuse, compressor overloads, an internal thermostat, a compressor contactor, and a refrig- erant high pressure cutout.

SAFETY CONTROL SETTINGS Ð The pumpout unit high- pressure switch (Fig. 1) is set to open at the settings listed in Table 5. The switch setting is checked by operating the pumpout condenser and slowly throttling the pumpout con- denser water.

Table 5 Ð High Condition Pressure Switch Settings

English

REFRIGERANT	HIGH-PRESSURE SWITCH
	Cutout	CutIn
R-134a	161 ± 5 psig		+ 0
		130	− 5 psig
R-22	220 ± 5 psig		+ 0
		185	− 5 psig
	SI
REFRIGERANT	HIGH-PRESSURE SWITCH
	Cutout	Cut-In
R-134a	1110 ± 34 kPa		+ 0
		896	− 34 kPa
R-22	1517 ± 34 kPa		+ 0
		1276	− 34 kPa

NOTES:

1.R-22 units use high-pressure cutout switch HK01UA181.

2.R-134a units use high-pressure cutout switch HK01UA187.

COMPRESSOR Ð The pumpout compressor assembly has a positive displacement of 1750 rpm (29 r/s) and 8.7 cfm (0.004 m3/s). It comes equipped with thermal protection on the motor and an in-line oil separator.

CONDENSER Ð The water-cooled condenser is fully ASME constructed. During transfer, it condenses refrigerant vapor to liquid. The condenser transfer tank safety relief valves com- ply with ASHRAE 15 standards.

OIL SEPARATOR Ð The pumpout unit includes an in-line oil separator to remove oil that becomes mixed with refrig- erant and returns the oil to the compressor.

SUCTION AND DISCHARGE VALVES Ð The pumpout unit comes with a 4-way transfer valve manifold to inter- connect both liquid and vapor transfer and to pressurize the chiller during transfer of refrigerant from chiller to storage tank or from one chiller vessel to another.

Storage Tank Ð The storage tank is rated for positive pressure refrigerants under ASME Section VIII pressure ves- sel codes with a minimum of 300 psig (2068 kPa) rating. The tank components include:

DRAIN VALVE Ð Located at its lowest point of drain with a minimum of 1 in. NPT.

DUAL RELIEF VALVES Ð Two relief valves and a 3-way shut-off valve.

PRESSURE GAGE Ð A 30 in.-0-400 psig (101-0-2760 kPa) compound pressure gage.

LEVEL GAGE Ð Liquid level gage (magnetically coupled dial type) with electronic shut-off at 90% liquid capacity.

During transfer of refrigerant into and out of the pump- out storage tank, carefully monitor the storage tank level gage. Do not ®ll the tank more than 90% of capacity to allow for refrigerant expansion. Over®lling may result in damage to the tank and personal injury. For maxi- mum refrigerant capacity, refer to Table 2.

OPERATION

Overview Ð Transferring refrigerant from one vessel to another is accomplished by using either gravity or pressure differential. A difference in elevation between 2 vessels re- sults in a gravity ¯ow of liquid; a difference in pressure forces the liquid from one vessel to the other. The latter method requires lowering the pressure in one vessel. If there is liq- uid in that vessel, its temperature must be lowered, and the pressure in the other vessel must be simultaneously increased.

Under most circumstances, creating the pressure differ- ential is not a difficult process. Some applications, such as ice storage, outdoor installations, or installations with high temperature differentials between the storage tank and the chiller may require additional consideration. In some in- stances, it may be necessary to add auxiliary heat to one of the vessels or to insulate the storage tank at job sites where high ambient temperature or sun load make it difficult to re- duce the temperature and pressure in the tank. Outdoor in- stallations must have a roof or cover over the storage tank to ensure that the pressure in the tank does not exceed the chiller relief pressure setting.

REFRIGERANT TRANSFER Ð When refrigerant is being evacuated from the chiller cooler or condenser vessels, any liquid refrigerant left in a vessel will ¯ash off, lowering the temperature in that vessel enough to freeze the ¯uid (usually water) ¯owing through the cooler or condenser tubes. This event, called tube freeze-up, can cause extensive damage to the chiller; therefore, all liquid refrigerant must be removed from a vessel before evacuation of refrigerant vapor is started. If all the liquid cannot be removed, then the cooler water and condenser water pumps must be operated throughout the process of evacuating refrigerant vapor to keep ¯uid moving through the cooler and condenser tubes.

TRANSFERRING LIQUID REFRIGERANT FROM THE CHILLER COOLER TO THE CHILLER CONDENSER OR PUMPOUT STORAGE TANK Ð Chiller and pumpout unit valves are set to permit the pumpout compressor to dis- charge refrigerant vapor into the cooler vessel, lowering pres- sure in the condenser vessel/storage tank. The pressure dif- ferential forces liquid from the cooler vessel into the condenser vessel/storage tank. After all the liquid is transferred, the re- frigerant vapor remaining in the cooler vessel can be drawn off by reducing pressure in the chiller and discharging the vapor through the pumpout unit condenser into the con- denser vessel/storage tank.

TRANSFERRING LIQUID REFRIGERANT FROM THE CHILLER CONDENSER OR PUMPOUT STORAGE TANK TO THE CHILLER COOLER Ð Chiller and pumpout unit valves are set to increase pressure in the chiller condenser vessel/storage tank and to reduce pressure in the cooler ves- sel. Pressure in the cooler vessel is lowered to correspond to a saturated refrigerant liquid temperature 2 F (1.1 C) above the freezing temperature of the liquid circulating through the chiller cooler/condenser tubes (34 F [1.1 C] for water). The valves are set so that the pressure in the cooler vessel is lower than that of the condenser vessel/storage tank, forcing the liquid into the cooler vessel.

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