Rev 3.1 01/11/23 - 18 - Model 600 User Guide
• The current lead system has a control voltage loss alarm.
• The controlling temperature has exceeded the L2 high temperature alarm level.
4.2 Controlling temperature
The system will make all control for the HVAC system based upon the “controlling temperature”. The
controlling temperature is defined in the system setup to be either zone sensor 1, zone sensor 2, the
average of both sensors, or the highest reading of the two sensors. If one of either the zone 1 or 2
sensor is selected, the system will use that sensor provided there is a valid reading (between -25-150°F).
If there is no valid reading then the system will report a sensor error on the display, turn both supply
fans on and turn off heating and cooling.
When using the average or high of the two sensors, the system will use that function provided both
sensors have valid readings. If one sensor is in error, then the Model 600 Controller will only use the
sensor with valid readings. If there is no valid reading from either sensor then the system will report a
sensor error on the display, turn the supply fans on and turn off heating and cooling.
The controlling temperature point will have write capability to allow the ESB2 (remote controller) to
write a value to the point. The Model 600 Controller will use the written value for control unless a
communications fault is detected. When a communications fault occurs, the controller will default back
to the defined controlling temperature sensor mode. See section 6 for additional information on remote
communications.
4.3 Fan control
The supply fan outputs are programmable from the display for continuous run for the lead system, both
fans continually run or automatic mode. Automatic operation means the fan output is turned on when
there is a call for heating, economization or cooling. For automatic mode, the fan will stay on until a
user-definable delay after heating, econ or cooling is turned off. The Residual Fan Delay default is 30
seconds but is user selectable from 0-300 seconds.
4.4 Cooling Mode
Once a stage of cooling is turned on, it must remain on until the controlling temperature is below the
cooling off setpoint (cool spt – cool off delta).
There are minimum on and minimum off time delays for each stage. These timers must elapse before
there can be a change of state on the output relays. For example, if a mechanical cooling stage is off, it
must be off for the minimum delay time before it allowed to be turned on. Once it is running, the
cooling must continue to run for at least the minimum on time. The only exception is if there is an alarm
condition that requires the cooling to be turned off such as a smoke alarm.
The Model 600 won’t “jump” a cooling stage based on controlling temperature. As in, if the unit is off
and calculations would like the unit to be in cool2, the unit will first try cool1 (or even econ if
calculations allow) for the minimum on time before moving to cool2.
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