Lennox LGT Series Unit Information page 43

K-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 dai-
sychained to the L Connection
For ease of configuration, the A55 can be connected to a
PC with Unit Controller PC software installed.
L-Indoor Air Quality (CO2) Sensor A63
The indoor air quality sensor monitors CO2 levels and
reports the levels to the A55 Unit Controller. The board
adjusts the economizer dampers according to the CO2
levels. The sensor is mounted next to the indoor thermo-
stat or in the return air duct. Refer to the indoor air qual-
ity sensor installation instructions for proper adjustment.
Wiring for the indoor air quality switch is shown on the
temperature control section (C2) wiring diagram in back
of this manual.
M-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 Control-
ler (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
Controller 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 af-
ter the switch has closed to restore unit operation.
N-Smoke Detectors A17 and A64
Photoelectric smoke detectors are a factory installed op-
tion. The smoke detectors can be installed in the supply
air section (A64), return air section (A17), or in both the
supply and return air section. Wiring for the smoke detec-
tors are shown on the temperature control section (C2)
wiring diagram in back of this manual.
Network Control System.
®
O-Factory Installed-Hot Gas Reheat (optional)
General
Hot Gas Reheat units provide a dehumidifying mode of op-
eration. These units contain a reheat coil adjacent to and
downstream of the evaporator coil. Reheat coil solenoid
valve, L14, routes hot discharge gas from the compressor
to the reheat coil. Return air pulled across the evaporator
coil is cooled and dehumidified; the reheat coil adds heat
to supply air. See figure 34 for reheat refrigerant routing
and figure 35 for standard cooling refrigerant routing.
P-Optional Cold Weather Kit (Canada only)
Electric heater is available to automatically control the
minimum temperature in the gas burner compartment.
Heater is C.G.A. certified to allow cold weather operation
of unit down to -60° F (-50° C ).
The kit includes the following parts:
1 - A heater assembly is installed on the vestibule of
the heating compartment. Included in the box are
the following:
a. Electric strip heat (HR6).
b. Thermostat switch (S59) is an auto-reset SPST
N.C. switch which opens on a temperature drop.
The switch is wired in series with 24v power
and the combustion air blower switch. When
the temperature drops below -30° F (-35°C) the
switch opens and the gas heat section is de-
energized. The switch automatically resets when
the heating compartment temperature reaches
-10° F (-12° C).
c. Thermostat switch (S60) is an auto-reset SPST
N.C. switch which opens on a temperature rise.
The switch is wired in series with HR6. When the
temperature rises above 20° F (-7° C) the switch
opens and the electric heater is de-energized.
The switch automatically resets when the heating
compartment temperature reaches -10° F (23.3°
C).
d. Thermostat switch (S61) is an auto-reset SPST
N.O. switch which closes on a temperature
drop. The switch is wired in series with HR6.
When temperature drops below 20° F (-7° C) the
switch closes and electric heater is energized.
The switch automatically opens when heating
compartment temperature reaches 76° F (24° C).
2 - K125 heat shutoff relay de-energizes HR6 heaters
when S60 or S61 thermostat switches open. K125
must be installed in the control section.
3 - Wire harness is routed between the heat section
components and the unit control box. Follow
instructions provided with kit for wire connections.
Page 43