User Manual

Mixing Box Control Installation Manual
IOM-MBC-00 08-30-04
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Mixing Box Control Systems
Titus offers two types of mixing box control system
packages, they are:
• Three-Position Control System.
• Modulating Control System.
The following segments discuss each system and its
components in detail, with the exception of the ball joints
and pushrods. The setup shown in Figure 1 is logic
module connected to a damper motor in a dedicated
arrangement.
Figure 1. Dedicated Logic Module and Damper Motor
Arrangement
Integrated Economizer System Operation
The purpose of an economizer is to use outdoor air for
cooling, whenever possible, to reduce compressor
operation. An economizer control system includes a
cooling thermostat and a solid-state enthalpy changeover
sensor. This allows it to respond to both dry bulb
temperature and humidity, allowing the use of outdoor air
temperatures for free cooling when humidity is low.
The
economizer functions as a first stage of cooling and
provides maximum economy during the cooling cycle. The
economizer is automatically locked out during heating by
holding the outdoor air damper at the minimum position
setting.
On a call for cooling by the space thermostat, the system
operates as follows:
When the sensed enthalpy of the outdoor air is below the
set point, the outdoor air damper is modulated open (and
return air damper is modulated closed) to maintain
between 50 and 56º Fahrenheit at the
mixed/discharge air
sensor. The second stage cooling uses the mechanical
cooling during the economizer operation.
When the sensed enthalpy of the outdoor air is above the
set point, the outdoor air damper closes to its minimum
position. On a call for cooling from the space thermostat
brings on mechanical cooling.
During the unoccupied period, the damper motor will
spring return the outdoor air damper to full closed position.
Diagnostic Equipment
In addition to either control system package, the following
diagnostic equipment (supplied
by others) may be
beneficial to the installation, verification, and/or
troubleshooting processes.
• 1.2k ohm checkout resistor
• Remote minimum position potentiometer
• Minimum position potentiometer
• Remote bulb control for low ambient lockout
• Board for panel mounting logic module
Three-Position Control System
Components list of the three-position control system is as
follows:
Table 1. Package Contents
Part Code Description Quantity
M8405A Three-position Damper Motor 1
W7459C Logic module 1
C7400A Solid state enthalpy sensor 1
27518 Ball joints 2
27520E 18-inch pushrods 2
Three-position Damper Motor – M8405A
Spring-return, 25-inch/pound damper motor (actuator)
provides three-position control of economizer systems or
ventilation dampers. Spring returns motor shaft to normal
position on power interruption. The following figure depicts
a damper motor.
Note: Damper motors may be referred to as
actuators.