Carrier 30GN040-420 Keypad and Display Module Also Called Hsio, Stop, Local/Enable

also controls the EXV driver module (as appropriate), com- manding it to open or close each EXV in order to maintain the proper superheat entering the cylinders of each lead com- pressor. Information is transmitted between the processor mod- ule and relay module, the EXV driver module, and the key- pad and display module through a 3-wire communications bus. The options module is also connected to the commu- nications bus.

For the Flotronic™ II chillers, the processor monitors sys- tem pressure by means of 6 transducers, 3 in each lead com- pressor. Compressor suction pressure, discharge pressure, and oil pressure are sensed. If the processor senses high dis- charge pressure or low suction pressure, it immediately shuts down all compressors in the affected circuit. During opera- tion, if low oil pressure is sensed for longer than one minute, all compressors in the affected circuit are shut down. At start- up, the oil pressure signal is ignored for 2 minutes. If shut- down occurs due to any of these pressure faults, the circuit is locked out and the appropriate fault code is displayed.

Low-Voltage Relay Module Ð This module closes contacts to energize compressor unloaders and/or compres- sors. It also senses the status of the safeties for all compres- sors and transmits this information to the processor.

Electronic Expansion Valve Module (If So Equipped) Ð This module receives signals from the pro- cessor and operates the electronic expansion valves.

Options Module Ð This module allows the use of Flo- tronic II features such as dual set point, remote reset, de- mand limit, hot gas bypass, and accessory unloaders. The options module also allows for reset and demand limit to be activated from a remote 4-20 mA signal. The options mod- ule is installed at the factory.

Keypad and Display Module (Also Called HSIO

or LID) Ð This device consists of a keypad with 6 func- tion keys, 5 operative keys, 12 numeric keys, and an alpha- numeric 8-character LCD (liquid crystal display). Key us- age is explained in Accessing Functions and Subfunctions section on page 24.

Control Switch Ð Control of the chiller is de®ned by the position of the LOCAL/ENABLE-STOP-CCN switch. This is a 3-position manual switch that allows the chiller to be put under the control of its own Flotronic II controls, manu- ally stopped, or put under the control of a Carrier Comfort Network (CCN). Switch allows unit operation as shown in Table 2.

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

Table 2 Ð LOCAL/ENABLE-STOP-CCN

Switch Positions and Operation

SWITCH	UNIT	CONFIGURATION AND
		SET POINT CONTROL
POSITION	OPERATION
		Keypad Control	CCN Control
STOP	Unit Cannot Run	Read/Write	Read Only
LOCAL/ENABLE	Unit Can Run	Read/Limited Write	Read Only
CCN Stop Ð	Unit Cannot Run	Read Only	Read/Write
Run Ð	Unit Can Run	Read Only	Read/Limited
			Write

In the CCN position, the chiller is under remote control and responds only to CCN network commands. The occupied/ unoccupied conditions are de®ned 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.

Electronic Expansion Valve (EXV) Ð The micro- processor controls the EXV (if so equipped) through the EXV driver module. Inside the expansion valve is a linear actua- tor 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 converts the pres- sure reading to a saturated temperature. The difference be- tween the temperature of the superheated gas and the satu- ration temperature is the superheat. The microprocessor controls the position of the electronic expansion valve stepper motor to maintain 30 F (17 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.

Thermostatic Expansion Valves (TXV) Ð Model 30GN040 and 045 units with factory-installed brine option are equipped with conventional thermostatic expansion valves with liquid line solenoids. The liquid line solenoid valves are not intended to be a mechanical shut-off. When service is required, use the liquid line service valve to pump down the system.

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