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
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.
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
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
Control Switch Ð Control of the chiller is de®ned by the position of the
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
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
Thermostatic Expansion Valves (TXV) Ð Model 30GN040 and 045 units with
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