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Figure 16: Vent And Combustion Air Hood
An adhesive backed label is provided over the outside of
the combustion air inlet opening to prevent moisture
from entering the unit, which could cause damage to
electrical components. Allow this closure label to remain
in place until the combustion air hood is to be installed.
Options/Accessories
Electric Heat
Electric heaters are available as factory-installed options or
field-installed accessories. Refer to electric heat instructions for
installation. These heaters mount in the heat compartment with
the heating elements extending into the supply air chamber. All
electric heaters are fused and intended for use with single point
power supply.
Economizer/Motorized Damper and Rain Hood
The instruction for the optional economizer/motorized damper
rain hood can be found in form 5004998. Use these instructions
when field assembling an economizer rain hood onto a unit. The
outdoor and return air dampers, the damper actuator, the
damper linkage, the outdoor and return air divider baffles, and all
the control sensors are factory mounted as part of the "Factory
installed" economizer/motorized damper options.
Power Exhaust/barometric Relief Damper and Rain Hood
The instructions for the power exhaust/barometric relief damper
and rain hood can be found in form 1200060.
All of the components, including the dampers, hardware, and
mounting instructions are shipped in a single package external
from the unit and must be field assembled and installed.
Power exhaust is only available as a field installed accessory.
Economizer And Power Exhaust Set Point
Adjustments
Remove the top rear access panel from the unit. Locate the
economizer control module, where the following adjustments
will be made.
Johnson Controls Unitary Products
Extreme care must be exercised in turning all set point,
maximum and minimum damper positioning adjustment
screws to prevent twisting them off.
Minimum Position Adjustment
• Check that the damper blades move smoothly without
binding; carefully turn the Minimum Position Adjust screw
(found on the damper control module) fully clockwise and
then set the thermostat indoor fan switch to the ON
position and then OFF or energize and de-energize
terminals "R" to "G".
• With the thermostat set to the indoor fan ON position or
terminals "R" to "G" energized, turn the Minimum Position
Adjusting screw (located on the damper control module)
counterclockwise until the desired minimum damper
position has been attained.
installation comes in the accessory.
Economizer Sequences
Several functions can drive the economizer, including: minimum
position, free cooling, economizer loading, and minimum
outdoor air supply.
Economizer Minimum Position
The economizer minimum position is set during occupied mode
when outside air is not suitable for free cooling. The position of
the damper is set proportionally between the "Economizer
Minimum Position and the Economizer Minimum Position Low
Speed Fan" set points, in relationship to the VFD output
percentage. On a constant volume single speed supply fan
system both set-points should be set to the same value.
Free Cooling
Four types of free cooling options are available: dry bulb
changeover, single enthalpy, dual enthalpy changeover, and
Auto.
Dry Bulb Changeover
For dry bulb economizer operation, the outside air is suitable for
free cooling if the outside air temperature is 1°F below the
Economizer OAT Enable Setpoint and 1°F below the Return Air
Temperature.
Free cooling is no longer available if the outside air temperature
rises above either the Economizer OAT Enable setpoint or the
return air temperature.
Single Enthalpy Changeover
For single enthalpy economizer operation, the outside air is
suitable for free cooling if the outside air enthalpy is at least 1
BTU/lb below the Economizer Outside Air Enthalpy Setpoint
5121817-TIM-A-0515
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