Unit Operation
In Occupied mode, the controller operates according to the occupied setpoints. In Occupied Standby Mode, the unit controller operates according to the Occupied Standby setpoints. When the controller receives a communicated unoccupied request, the controller
operates according to the unoccupied setpoints regardless of the state of the hardwired occupancy input.
If neither the binary input nor the communicated input is used to select the occupancy mode, the
controller defaults to occupied mode because the occupancy binary input (if present) typically is configured as normally open without an occupancy device connected.
Table 4: Normally open hardwired input configuration (BI 3)
Description | Communicated Request | Hardwired State | Result |
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|
|
|
Standalone | NA | Open = Occupied | Occupied |
|
|
|
|
Standalone | NA | Closed = Unoccupied | Unoccupied |
|
|
|
|
Communicating | Occupied | Open = Occupied | Occupied |
|
|
|
|
Communicating | Unoccupied | Open = Occupied | Unoccupied |
|
|
|
|
Communicating | Occupied Standby | Open = Occupied | Occupied Standby |
|
|
|
|
Communicating | Occupied | Closed = Occupied Standby | Occupied Standby |
|
|
|
|
Communicating | Unoccupied | Closed = Occupied Standby | Unoccupied |
|
|
|
|
Communicating | Occupied Standby | Closed = Occupied Standby | Occupied Standby |
|
|
|
|
Note:
If configured for normally closed, all states are opposite of Table 4.
Generic Binary Input
Building automation systems can monitor the status of the generic binary input. This input does not affect controller operation.
High and Low Pressure
Switches
The high and low pressure cutout switches are wired in series with the compressor contactor in the unit. The ZN510 controller detects the state of each switch circuit by monitoring the controller’s compressor triac outputs. If either the high pressure switch (HPC) or the low pressure switch (LPC) switch opens, a fault condition occurs. This open circuit prevents the
compressor contactor from energizing keeping the compressor from running. The controller automatically detects the fault condition by measuring the compressor triac output signal.
By default, when the HPC or LPC switches detect a high or low pressure condition in the refrigerant circuit, the special input detects the diagnostic and disables all compressor operation for that circuit. The unit fan continues to operate, if only one circuit is disabled in a two compressor unit. When the HPC/LPC diagnostic is present on both circuits, the ZN510 shuts off the unit fan and disables
unit operation. See Figure 7 for high and low pressure switch.
When the refrigerant circuit returns to normal, the HPC and the LPC switches automatically reset. The high or low pressure cutout diagnostic may need to be manually reset to clear the diagnostic and enable compressor operation for the fault circuit.
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