86
McQuay IM 487-4
Unit Options
Duct High Pressure Limit
The duct high pressure limit control (DHL) is provided on all
VAV units. The DHL protects the duct work, the terminal
boxes, and the unit from over pressurization, which could be
caused by, for example, tripped fire dampers or control failure.
The DHL control is factory set to open when the discharge
plenum pressure rises to 3.5" w.c. (872 Pa). This setting should
be correct for most applications; however, it is adjustable.
Removing the front cover of the device reveals a scale
showing the current setting. Turning the adjustment screw
(located on the bottom of the device) adjusts the setting up or
down.
If the DHL switch opens, digital input MCB BI 14 on the Main
Control Board will be de-energized. The MicroTech II
controller then shuts down the unit and enters the Off-Alarm
state. The alarm must be manually cleared before the unit can
start again. Refer to the operation manual supplied with your
unit for more information on clearing alarms (OM138 or
OM137).
MicroTech II™ Remote User Interface (UI)
Both a unit mounted and an identical, remote mounted keypad
and display are provided with this option. A remote-mounted
user interface (UI) is available as an option with all rooftop
units. The following items are provided:
•
Unit mounted UI
•
Unit mounted power supply and R485 isolator for the
remote UI
•
Selector switch to activate either the unit mounted UI or the
remote UI. Only one UI is active at a time.
•
Wall mounted electrical box that contains the remote UI. See
Figure 93.
Cable and Wiring Recommendations
Remote wiring to connect the unit to the remote UI is not
included. See Figure 94 on page 86 for wiring information and
the following recommendations.
•
No more than 1200 feet of wiring can be used to connect the
remote user interface to the unit.
•
Use overall foil shield, 3 twisted pairs, 22 AWG stranded
connectors with drain wire.
•
UL 910 plenum rated = Belden 6542FE-1000-877
•
Non-plenum rated = Belden 5542FE-1000-8
Figure 93. Factory-assembled remote user interface
Figure 94. Remote user interface wiring diagram
Surface Mount,
Modular Jack
with 6 contacts,
Screw Terminals
Enclosure
with Cover
(4) #6-32
Hex Nuts
(4) #6 Split
Lock Washers
Ground
Keypad/Display
Module
Cable Assembly
6.9 "
7.2 "
4.4 "
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