Carrier 040-420 Compressor Protection Control Module Cpcs, Thermistor and Transducer Locations

In the LOCAL/ENABLE position, the chiller is under lo- cal control and responds to the scheduling configuration and set point data input at its own local interface device (key- pad and display module).

In the CCN position, the chiller is under remote control and responds only to CCN network commands. The occupied/ unoccupied conditions are defined by the network. All key- pad and display functions can be read at the chiller regard- less of position of the switch.

CCN run or stop condition is established by a command from the CCN network. It is not possible to force outputs from the CCN network, except that an emergency stop com- mand shuts down the chiller immediately and causes ‘ ‘ALARM 52” to be displayed.

Table 2 - LOCAL/ENABLE-STOP-CCN

Switch Positions and Operation

S W I T C H		I	U N I T		CONFIGURATION AND
					SET POINT CONTROL
P O S I T I O N		OPERATION
					Keypad Control 1CCN Control
STOP	I Unit		Cannot	Run	Read/Write	1 Read Only
LOCAL/ENABLE		Unit	Can Run		Read/Limited Write	Read Only
		Unit Cannot Run			Read Only	ReadlWrite
CCN :t2 1		Unit	Can Run		Read Onlv	Read/Limited Write

Electronic Expansion Valve (EXV) - The micro- processor controls the EXV through the EXV driver mod- ule. Inside the expansion valve is a linear actuator stepper motor.

The lead compressor in each circuit has a thermistor and a pressure transducer located in the suction manifold after the compressor motor. The thermistor measures the tem- perature of the superheated gas entering the compressor cyl- inders. The pressure transducer measures the refrigerant pressure in the suction manifold. The microprocessor con- verts the pressure reading to a saturated temperature. The difference between the temperature of the superheated gas and the saturation temperature is the superheat. The micro- processor controls the position of the electronic expansion valve stepper motor to maintain 29 F (16 C) superheat.

At initial unit start-up, the EXV position is at zero. After that, the microprocessor keeps accurate track of the valve position in order to use this information as input for the other control functions. The control monitors the superheat and the rate of change of superheat to control the position of the valve. The valve stroke is very large, which results in very accurate control of the superheat.

Sensors - The Flotronic TM 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 - Thermistor and Transducer Locations

	THERMISTORS
Sensor	Location

Cooler Leaving Water Temp

T:Cooler Entering Water Temp Compressor Suction Gas Temp Circuit A

Ti	Compressor Suction Gas Temp Circuit B
TIO	Remote Temperature Sensor (Accessory)
	PFIESSURETRANSDUCERS
Sensor			Location
DPT - A	Compressor	Al	Discharge Pressure
SPT - A	Compressor Al Suction-Pressure
OPT - A	Compressor	Al	Oil Pressure
DPT-I3	Compressor	Bl	Discharge Pressure
SPT - B	Compressor	Bi	Suction Pressure
OPT - B	Compressor	Bl	Oil Pressure

Compressor Protection Control Module (CPCS)

- Each compressor on models 30GN070 (50 Hz), 080- 100, and 240B, 270B, has its own CPCS as standard equip- ment. All 30GN040-060 and 070 (60 Hz) units feature the CPCS as an accessory, and CR (control relay) as standard equipment. See Fig. 2. The 30GN130-2 10 and associated modular units and the 30GT225, 250, and 280 Flotronic II 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 protec- tion. Ground current protection is accomplished by using a CGF (compressor ground fault) board in conjunction with the CR. The CGF 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 signal contacts, it will lock the compressor off by deener- gizing the proper 24-v control relay on the relay board. The CPCS board contains logic that can detect if the current-to- 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 compressor in either circuit is shut down by the high pres- sure switch or ground current protector, all compressors in the circuit are locked off.

PROTECTION BOARD

Fig. 2 - Compressor Protection Control Module

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