Rev 3.1 01/11/23 - 20 - Model 600 User Guide
4.6.1.1 Adjusting OSA Setpoints
The Model 600 Controller will float/adjust the economizer OSA setpoint by using the Quest patented
algorithm. Successfully cooling with OSA will move the L1 and L2 setpoints up. Failure to cool the zone
with OSA only will cause the setpoints to adjust down. It is recommended that the differential between
L1 and L2 be 3 to 5 degrees. The default is three degrees. An additional setting is provided called L1/L2
Max Change. This is the maximum allowable degrees that L1 and L2 will be allowed to move up or
down. Both settings move together to maintain the differential.
4.6.2 Integrated Econ Control
Integrated economizer control means the economizer is being controlled by the HVAC system. The
Model 600 Controller will decide to turn on stage 1 of cooling. The HVAC system will then decide to use
economization or mechanical cooling. If temperature continues to rise, the Model 600 Controller will
turn on output 2 to force mechanical cooling. This will cause the HVAC system to switch to mechanical
cooling.
4.6.3 No Economization
The system allows for the option of NONE for the economization question. Choosing this option will
disable all economizer logic and will control the mechanical cooling based upon the cooling setpoints.
4.7 Dehumidification mode
The dehumidification mode will be used to reduce the humidity inside the facility. When the relative
humidity is greater than the dehumidification setpoint, the controller will change the operational
cooling and heating setpoints to the Dehumidify cooling and heating setpoints. A user will typically
move the cooling setpoint way down so the air conditioning can take moisture out of the air. A user can
also move the heating setpoint to facilitate dehumidification. Economization will be disabled during
dehumidification mode.
5 Alarm Sequence of Operation
All alarm conditions in this section will cause a message about the alarm to be displayed on line 2 of the
local display. The display will rotate through all alarm messages if there is more than one active alarm
condition. In addition, there are six form C outputs used for specific alarms. The outputs are energized
under normal conditions and de-energized when in alarm.
5.1 High Temperature Level 2
The Model 600 Controller will compare the controlling temperature to the high temperature alarm L2
setpoint and alarm if the controlling temperature is greater than the setpoint for one minute. The alarm
will clear when the controlling temperature is below the high temp L2 setpoint minus 2 degrees for 1
minute. Alarm Output 2 is used for High Temp Level 2 alarms along with an alarm message on the front
display and status via Modbus.
5.2 High Temperature Level 1
The Model 600 Controller will compare the controlling temperature to the high temperature alarm L1
setpoint and alarm if the controlling temperature is greater than the setpoint for one minute. The alarm
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