Carrier 30GN Chiller Manual: Essential Insights for Your 30GN Unit

The TXV is set at the factory to maintain approximately 8 to 12° F (4.4 to 6.7° C) suction superheat leaving the cooler by monitoring the proper amount of refrigerant into the cooler. All TXVs are adjustable, but should not be adjusted unless absolutely necessary. When TXV is used, thermistors T7 and T8 are not required.

The TXV is designed to limit the cooler saturated suction temperature to 55 F (12.8 C). This makes it possible for unit to start at high cooler ¯uid temperatures without overload- ing the compressor.

Sensors Ð The Flotronic™ II chiller control system gath- ers information from sensors to control the operation of the chiller. The units use 6 standard pressure transducers and 4 standard thermistors to monitor system pressures and tem- peratures at various points within the chiller. Sensors are listed in Table 3.

Table 3 Ð Thermistor and Transducer Locations

	THERMISTORS
Sensor	Location
T1	Cooler Leaving Fluid Temp
T2	Cooler Entering Fluid Temp
T7	Compressor Suction Gas Temp Circuit A
T8	Compressor Suction Gas Temp Circuit B
T10	Remote Temperature Sensor (Accessory)
	PRESSURE TRANSDUCERS
Sensor	Location
DPT-A	Compressor A1 Discharge Pressure
SPT-A	Compressor A1 Suction Pressure
OPT-A	Compressor A1 Oil Pressure
DPT-B	Compressor B1 Discharge Pressure
SPT-B	Compressor B1 Suction Pressure
OPT-B	Compressor B1 Oil Pressure

Compressor Protection Control Module (CPCS)

ÐEach compressor on models 30GN070 (50 Hz), 080- 110, and 230B-315B, has its own CPCS as standard equip- ment. See Fig. 2. All 30GN040-060 and 070 (60 Hz) units feature the CPCS as an accessory, and CR (control relay) as standard equipment. The 30GN130-210 and associated modu- lar units have a CR as standard equipment. The CPCS or CR is used to control and protect the compressors and crankcase heaters. The CPCS provides the following functions:

· compressor contactor control · crankcase heater control

· compressor ground current protection

· status communication to processor board · high-pressure protection

The CR provides all of the same functions as the CPCS with the exception of compressor ground current protection. Ground current protection is accomplished by using a CGF (compressor ground fault module) in conjunction with the CR. The CGF (See Fig. 3) provides the same ground fault function as the CPCS for units where the CPCS is not utilized.

One large relay is located on the CPCS board. This relay (or CR) controls the crankcase heater and compressor contactor. The CPCS also provides a set of signal contacts that the microprocessor monitors to determine the operating status of the compressor. If the processor board determines that the compressor is not operating properly through the sig- nal contacts, it will lock the compressor off by deenergizing the proper 24-v control relay on the relay board. The CPCS board contains logic that can detect if the current-to-

Fig. 2 Ð Compressor Protection Control Module

Fig. 3 Ð Compressor Ground Fault Module

ground of any compressor winding exceeds 2.5 amps. If this condition occurs, the CPCS module shuts down the compressor.

A high-pressure switch with a trip pressure of 426

±7 psig (2936 ± 48 kPa), is wired in series with the CPCS. If this switch opens during operation, the compressor stops and the failure is detected by the processor when the signal contacts open. The compressor is locked off. If the lead com- pressor in either circuit is shut down by the high-pressure switch or ground current protector, all compressors in the circuit are locked off.

OPERATION DATA

Capacity Control Ð The control system cycles compressor to give capacity control steps as shown in Tables 4A-4C. The unit controls leaving chilled ¯uid tem- perature. Entering ¯uid temperature is used by the micro- processor in determining the optimum time to add or sub- tract steps of capacity, but is not a control set point.

The chilled ¯uid temperature set point can be automati- cally reset by the return temperature reset or space and outdoor-air temperature reset features. It can also be reset from an external 4 to 20 mA signal, or from a network signal.

The operating sequences shown are some of many pos- sible loading sequences for the control of the leaving ¯uid temperature. If a circuit has more unloaders than another, that circuit will always be the lead circuit.

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