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I-Control Systems
The A55 Unit Controller provides all control function for the
rooftop unit. Default operation requires a standard room
thermostat or direct digital controller (DDC). The A55 can
also control the unit from a zone temperature sensor. The
A55 Unit Controller is a network controller when daisy-
chained to the L Connection
®
Network Control System. For
ease of configuration, the A55 can be connected to a PC
with Unit Controller PC software installed.
J-Smoke Detectors A171, A172, A173
Photoelectric smoke detectors are a factory- and field-in
stalled option. The smoke detectors can be installed in the
supply air section (A172), return air section (A171), or in both
the supply and return air section. Smoke detection control
module (A173) is located below the control panel. Wiring for
the smoke detectors are shown on the temperature control
section (C) wiring diagram in back of this manual.
K-Blower Proving Switch S52
The blower proving switch monitors blower operation and
locks out the unit in case of blower failure. The switch is
N.O. and closes at .15” W.C. (3.3 Pa) The switch is mount
ed on the middle left corner of the blower support panel.
Wiring for the blower proving switch is shown on the tem
perature control section (C) wiring diagram in back of this
manual.
L-Dirty Filter Switch S27
The dirty filter switch senses static pressure increase indi
cating a dirty filter condition. The switch is N.O. and closes
at 1” W.C. (248.6 Pa) The switch is mounted on the top cor
ner of the economizer. Wiring for the dirty filter switch is
shown on the temperature control section (C) wiring diagram in
back of this manual.
M-Optional UVC Lights
The Healthy Climate
®
germicidal light emits ultraviolet
(UVC) energy that has been proven effective in reducing
microbial life forms (viruses, bacteria, yeasts and molds) in
the air.
UVC germicidal lamps greatly reduce the growth and prolif
eration of mold and other bio-aerosols (bacteria and virus
es) on illuminated surfaces.
Germicidal lamps are NOT intended to be used for removal
of active mold growth. Existing mold growth must be appro
priately removed PRIOR to installation of the germicidal
lamp.
Refer closely to UVC light installation instruction warnings
when servicing units.
N-Drain Pan Overflow Switch S149 (optional)
The overflow switch is used to interrupt cooling operation
when excessive condensate collects in the drain pan.
The N.C. overflow switch is connected to the M2 Unit Con
troller (A55) through DI-3. When the switch opens, the Unit
Controller will shut off the unit. After a five-minute time out,
the Unit Controller will verify the overflow switch position
and restart the unit (if the switch has closed). The Unit Con
troller has a three-strike counter before the unit locks out.
This means the Unit Controller will allow the overflow switch
to open three times per thermostat demand. If the unit locks
out, a reset of the Unit Controller is required after the switch
has closed to restore unit operation.
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