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GENERAL INFORMATION
The flush mount ceiling plenum is designed for application in
systems that utilize field fabricated (OEM supplied) cold air
ducting. The ducting must be routed through the ceiling
cavity (between the interior ceiling and roof). Ducting
specifications are given in the section labeled “Supply Ducting
and Registers”.
This system utilizes a single, non-ducted centrally located
return air opening. The return air opening is contained within
the ceiling plenum. The ceiling plenum must be located
directly below the roof opening used for mounting the roof top
unit.
All manual controls have been removed from the ceiling
plenum. They have been replaced with control relays. The
relays are mounted in the electrical box of the ceiling plenum.
The relays contain 12 VDC coils (which are energized by a
wall mounted thermostat), with contacts that control the 115
VAC used to power the roof top unit.
All air conditioning functions are controlled by the low
voltage wall mounted thermostat. The thermostat controls a
12 VDC electrical circuit which is used to energize the relays
in the ceiling plenum. The thermostats that Airxcel, Inc.
provides for the system are combination (Heat/Cool)
thermostats. These thermostats are capable of operating both
the roof top air conditioner and any furnace with a 12 VDC
control circuit of 1 amp or less (continuous current).
All air conditioning equipment is subject to freeze up when
evaporator air flow is sufficiently reduced. Ducting of any
length creates potential for reduced evaporator air flow and
system freeze-up. To protect both the installer and Airxcel,
Inc. from conditions that promote reduced air flow and system
freeze-up, Airxcel, Inc. has equipped the ceiling plenum
compressor control circuit with a low temperature probe. The
low temperature probe monitors the temperature of the air
conditioner evaporator coil. When the temperature of the
evaporator coil drops below 28 degrees F, the switch will
open, stopping compressor operation. Compressor operation
will resume once the evaporator warms to 55 degrees F.
IMPORTANT
The low temperature sensor is part of the ceiling plenum
electrical circuit. The probe must be inserted into the
evaporator coil of the roof top unit by the installer when
bolting the ceiling plenum to the roof top unit.
The 8330 series ceiling assemblies will mount to and operate
all 47200, 48200 or 49200 series roof top air conditioners.
The 8530 series ceiling assemblies will mount to and operate
all 47000, 48000 or 49000 series roof top heat pumps.
CEILING PLENUM INSTALLATION REQUIREMENT
1.
The ceiling plenum must be installed under the roof
opening.
The ceiling plenum bolts below the roof top unit.
Compression of the framed ceiling cavity between
the roof top unit and the ceiling plenum is what holds
both components in place.
2.
Ceiling cavity depth (the measurement from the
ceiling to the roof – maximum 6”).
3.
The 115 VAC service for the roof top unit must be
routed into the ceiling plenum. To prevent wire
pinching and to promote ease of installation,
allowances must be made for routing the 115 VAC
supply wiring into the front of the roof opening.
4.
Thermostat wiring must be run from the wall
thermostat mounting location to the wirebox low
voltage terminals. To prevent wire pinching and to
promote ease of installation, allowances must be
made for routing the low voltage wiring into the
front of the opening.
5.
The wirebox has a 9 pin receptacle extending from
the front. This mates with the roof unit 115 volt
electrical conduit. When making this connection,
verify that the plugs are properly aligned and have
snapped together securely.
6.
A low voltage terminal strip on the front of the box
connects to the thermostat wires. The wires attach by
1/4" quick connects.
