Lennox CHA16, Service Manual

Page: 48 / 86

Page 48
H-Low Ambient Kit (all units)
The optional low ambient kit (figure 53) allows for mechan
ical cooling operation at low outdoor temperature.
NOTE-
See CAUTION.
CAUTION
Compressor monitor (Low Ambient Lockout Switch)
S3 cannot be used with optional low ambient kit.Com
pressor monitor MUST be disconnected before allow
ing low ambient kit to be used.
The components included in the low ambient kit vary from
unit to unit.Low ambient kits may include any combination
of a pressure switch, a low ambient thermostat or a relay.
WARNING
Electrical shock hazard. Low ambient kit wiring
changes depending on unit size. Depending on the
application, low ambient controls may be wired to low
voltage or line voltage. Be sure to disconnect power
to unit before servicing. Then check unit wiring dia
gram and become familiar with low ambient wiring be
fore proceeding.
The pressure switch, if used, is connected to the condens
er fan and the compressor discharge line. The pressure
switch senses a drop in outdoor temperature by monitor
ing the pressure of the discharge line. When discharge line
pressure drops below a preset limit, the pressure switch
opens the circuit to the condenser fan. With the condenser
fan deenergized, the discharge pressure will slowly in
crease. When discharge pressure increases above a pre
set limit the pressure switch closes the circuit to the con
denser fan and the fan resumes operation. The pressure
switch will continue to cycle the fan in this fashion as long
as low ambient conditions exist.
The low ambient thermostat, if used, is connected to the
second stage compressor. The switch monitors outdoor
temperature conditions and opens the circuit to the sec
ond stage compressor when outdoor temperture drops
below a preset limit. The second stage compressor re
mains disconnected from the circuit until outdoor tempera
ture rises above the preset limit.
The low ambient kit relay, if used, is typically used to sense
a call for compressor demand. When the relay coil is ener
gized, the contacts switch to complete a circuit through the
low ambient pressure switch.
FIGURE 53
TYPICAL INSTALLATION
LOW AMBIENT
PRESSURE SWITCH
HIGH PRESSURE
SWITCH
COMPRESSOR
DISCHARGE
LINE
LOSS OF
CHARGE
SWITCH
VALVE
DEPRESSOR TEE
SHOCK
LOOP
LOW AMBIENT KIT
Refer to low ambient kit installation instructions for de
tailed installation and operation information. Low ambient
kit wiring is shown on the unit wiring digrams in back of this
manual.
I-Status Panels SP11 and SSP11
Optional status panels allow remote monitoring of system
operation.Two types of panels are available.The SP11 (fig
ure 54) provides system readout only.The SSP11 switching
status panel (figure 55) is a combination switching subbase
and system readout.The SSP11 also has an After Hours
Timer" to override the unoccupied mode (night heating set
back / cooling setup).
FIGURE 54
SP11 STATUS PANEL
Cool Mode
Heat Mode
Compressor 1
Compressor 2
No Heat
Filter