The Time Guard® function maintains a minimum off time of 5 minutes, a minimum ON time of 10 seconds, and a minimum delay before starting the second compressor of 10 seconds.
If the compressors have been off for more than 15 minutes and the OAT
Heating and cooling will be mutually locked out on demand on a first call basis. The heating and the cooling functions can- not be operating simultaneously.
COOLING, VARIABLE AIR VOLUME (VAV) UNITS — On power up, the control module will activate the initialization software of the control board. The initialization software then reads DIP switch no. 1 position to determine CV or VAV oper- ation. Initialization clears all alarms and alerts,
The control module will determine if an interface (linkage) is active and if the unit will operate in a Digital Air Volume (DAV) mode. In a DAV system, the room terminals are equipped with microprocessor controls that give commands to the base unit module. If an interface is active, the control will replace local comfort set points, space and return air tempera- tures and occupancy status with the linkage data supplied.
The control module will determine occupancy status from Time Schedules (if programmed), Remote Occupied/Unoccu- pied input, global occupancy, or DAV. If Temperature Com- pensated Start is active, the unit will be controlled as in the Occupied mode.
NOTE: The temperature compensated start is a period of time calculated to bring the unit on while in Unoccupied mode to reach the occupied set point when occupancy occurs.
The control module will set the appropriate operating mode and fan control. The control module will turn VFD on if Occu- pied mode is evident.
For units equipped with a start/stop switch only (no space temperature sensor), if in Unoccupied mode and valid return- air temperature reading is available (either from a sensor or DAV), the control will monitor
For units with a start/stop switch and a space temperature sensor, the control module will start the VFD whenever SPT is outside of the set points (Unoccupied Heat or Unoccupied Cool). The VFD may also be started by nighttime thermostat via remote Occupied/Unoccupied input or by a Temperature Compensated Start algorithm. When VFD is running in a nor- mal mode, the control will start heating or cooling as required to maintain
When cooling, the control will energize the power exhaust enable output to the external power exhaust controller, when power exhaust is used.
If in Occupied mode, the control module will perform econ- omizer control (economizer control same as described above for CV units). If in Unoccupied mode, the control module will perform nighttime free cool and IAQ
The control will run continuous diagnostics for alarms/ alerts; respond to CCN communications and perform any con- figured network POC (product outboard controls) functions such as time and
GAS HEATING, CONSTANT VOLUME (CV) UNITS — The gas heat units incorporate 2
All of the gas heating control is performed through the IGC boards (located in the heating section). The control module board serves only to initiate and terminate heating operation.
The control module board is powered by 24 vac. When the thermostat or room sensor calls for heating, power is sent from the control module board to W on each of the IGC boards. An LED on the IGC board will be on during normal operation. A check is made to ensure that the rollout switches and limit switches are closed and the
When ignition occurs the IGC board will continue to moni- tor the condition of the rollout and limit switches, the hall effect sensor, as well as the flame sensor. If the unit is controlled through a room thermostat set for fan auto., 45 seconds after ignition occurs, the
If the unit is controlled with a room sensor in the Unoccu- pied mode, the indoor fan will be energized through the IGC board with a
When additional heat is required, W2 closes and initiates power to the second stage of the main gas valves. When the thermostat is satisfied, W1 and W2 open and the gas valves close interrupting the flow of gas to the main burners. If the call for W1 lasted less than 1 minute, the heating cycle will not ter- minate until 1 minute after W1 became active. If the unit is controlled through a room thermostat set for fan auto., the
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