Direct Gas Make-Up Air
39
Building Freeze Protection
This option is intended to disable the unit supply fan
in the event the discharge temperature falls below
35°F for five minutes. This is accomplished through
electromechanical controls or a microprocessor.
Building freeze protection is selected when the unit may
operate while the space it serves is unoccupied.
Carbon Dioxide (CO
2
) Sensor
This sensor is intended to measure the CO
2
concentra-
tion in the ventilated space or return air duct. If the unit
has been equipped with a microprocessor controller, the
CO
2
sensor will modulate either the VFD or the return
and outside air dampers based upon a comparison of
the CO
2
set point to the actual CO
2
levels reported from
the sensor. The duct mount or room mount sensor is
shipped loose for field mounting and wiring.
Duct-Mounted Smoke Detector
The duct smoke detector provides early detection of
smoke present in the HVAC duct system. The smoke
detector is designed to prevent the recirculation of
smoke by the air handling system. Complete system
shut down will occur in the event of smoke detection.
The detector will operate on 115 or 24 VAC. Output
terminals are provided for remote accessories such
as a horn, strobe, remote status indicators and reset
switches or push buttons.
Microprocessor Controls
The controller has been pre-programmed to offer
multiple control sequences for providing tempered air.
Easy monitoring and adjustment of unit parameters can
be accomplished by way of the lighted graphical display
and an integral push-button keypad or by way of the
Building Management System (BMS) communication
with the addition of an optional BMS communication
card. This addition allows the user too remotely adjust
set points, view unit status points and alarms. The
sequence parameters are fully adjustable. For additional
information, reference the supplemental Microprocessor
Controller for Make-Up Air Reference Guide for more
information.
Packaged Direct Expansion (PDX)
Cooling Module
The PDX module is a complete package that has
been designed for outdoor installations. The PDX
system in the module is a complete, sealed unit with
compressed R-410A refrigerant. It consists of one or
two compressors, evaporator and condenser coils,
and all other necessary components. Reference the
supplemental
Packaged DX Module
Installation,
Operation and Maintenance Manual for more
information.
Start-Up: Optional Features
Other
Dirty Filter Switch
To adjust the switch, the unit must be running with all of
the access doors in place, except for the compartment
where the switch is located. The filters must be clean
and in good condition. The adjusting screw is located
on the top of the switch.
Setscrew (on front of switch) must be manually
adjusted after the system is in operation.
Negative pressure connection is toward
the 'front or top' of the switch.
(Senses
pressure on the fan side of filters)
Positive pressure connection is toward the 'back or bottom' of
the switch.
(Senses pressure at the inlet side of filters)
1. Open the filter compartment and place a sheet of
plastic or cardboard over 50% of the filter media.
2. Close and secure the filter compartment door.
3. Check to see if there is power at the alert signal
leads (refer to electrical diagram).
4. If power is present, turn the adjustment screw
counterclockwise until the power goes off. Turn
slightly clockwise until power comes back on. If
power is not present, turn the adjustment screw
clockwise until the power comes on.
5. Open the filter compartment and remove the
obstructing material.
6. Close and secure the door and check to make sure
there is no power at the alert signal leads. The unit is
now ready for operation.
Heating and/or Cooling Inlet Air
Sensor(s)
The heating inlet air sensor locks out heating operation
when the inlet temperature rises above set point (field-
adjustable). The cooling inlet air sensor locks out
cooling when inlet temperature falls below set point
(field-adjustable). These components are located in the
unit’s control center. Reference the unit’s ladder diagram
for component identification and terminal designation.
Inlet Damper End Switch
Provides a damper actuator with an end switch that
is wired into the unit’s control center. This will prevent
the supply fan from starting up until the end switch
is proven. Reference the unit’s ladder diagram for
component identification and terminal designation.
