Lennox LCH092H Unit Information page 41

The A55 Unit Controller has a three-strike counter before
locking out. This means the control allows three high
pressure trips per one thermostat demand. The control
can be reset by breaking and remaking the thermostat
demand or manually resetting the control.
5-Low Ambient Switches S11, S84
The low ambient switch is an auto‐reset SPST N.O. pres­
sure switch which allows mechanical cooling operation
at low outdoor temperatures. On standard and high effi­
ciency units, the switches are located in each liquid line
prior to the indoor coil section. On ultra high efficiency
units, S11 (only) is located on the common liquid line pri­
or to the indoor coil section.
On standard and high efficiency units, S11 and S84 are
wired to the A55 Unit Controller which cycles outdoor fans
via K10 (outdoor fan 1) and K68 (outdoor fan 2). On ultra
high efficiency units, S11 is wired to the A55 Unit Controller
which cycles outdoor fan 1 (outdoor fans 2 and 3 are de-en­
ergized during low ambient operation).
When liquid pressure rises to 450 ± 10 psig (3102 ± 69
kPa), the switch closes and the condenser fan is ener­
gized. When discharge pressure in one refrigerant circuit
drops to 240 ± 10 psig (1655 ± 69 kPa), the switch opens
and the condenser fan in that refrigerant circuit is de-ener­
gized. This intermittent fan operation results in higher evap­
orating temperature allowing the system to operate without
icing the evaporator coil and losing capacity.
6-Low Pressure Switches S87, S88
The low pressure switch is an auto‐reset SPST N.O. switch
(held N.C. by refrigerant pressure) which opens on a pres­
sure drop. All units are equipped with this switch. The
switch is located in the compressor suction line.
On standard and high efficiency units, S87 (compressor
one) and S88 (compressor two) are wired to A55 Unit Con­
troller. On ultra high efficiency units, S87 (only) is located on
the common suction line and is wired to A55 Unit Controller.
A55 governs the low pressure switches by shunting the
switches during start up until pressure is stabilized. After
the shunt period, the control has a three‐strike counter, dur­
ing first thermostat demand, before the compressor is
locked out. The control is reset by breaking and remaking
the thermostat demand or manually resetting the control.
When suction pressure drops to 40 + 5 psig (276 ± 34
kPa), (indicating low pressure), the switch opens and the
compressor is de-energized. The switch automatically
resets when pressure in the suction line rises to 90 + 5
psig (620 ± 34 kPa) due to many causes such as refriger­
ant being added.
7-Service Valve (optional)
LCH units may be equipped with service valves located
in the discharge and liquid lines. The service valves are
manually operated valves used for service operation.
8-Filter Drier
LCH units have a filter drier located in the liquid line of each
refrigerant circuit at the exit of each condenser coil. The dri­
er removes contaminants and moisture from the system.
9-Freezestats S49 and S50
Standard and high efficiency units are equipped with a low
temperature switch (freezestat) located on the return
bend of each evaporator coil. S49 (first circuit) and S50
(second circuit) are located on the corresponding evapo­
rator coils. Ultra high efficiency units are equipped with
S49 only which is located on the return bend of the com­
mon evaporator coil.
Each freezestat is wired to the A55 Unit Controller. Each free­
zestat is a SPST N.C. auto-reset switch which opens at 29°F
+ 3°F (‐1.7°C + 1.7°C) on a temperature drop and closes at
58°F + 4°F (14.4°C + 2.2°C) on a temperature rise. To
prevent coil icing, freezestats open during compressor
operation to temporarily disable the respective com­
pressor until the coil warms sufficiently to melt any accu­
mulated frost.
If the freezestats are tripping frequently due to coil icing, check
the unit charge, airflow and filters before allowing unit back in
operation. Make sure to eliminate conditions which might pro­
mote evaporator ice buildup.
10-Condenser Fans B4, B5
See SPECIFICATIONS tables at the front of this manual
for specifications of condenser fans used in all units. All
condenser fans used have single-phase motors. The fan
assembly may be removed for servicing and cleaning.
Ultra High Efficiency Units Only
Ultra high efficiency units are equipped with electronically
commutated condenser fan motors (ECM). The ECM mo­
tors are wired directly to 230VAC power but do not operate
until a pulse width modulated (PWM) control signal is sent
from the A55 Unit Controller. The PWM signal determines
the condenser fan speed. All three fans will operate in low
speed with a Y1 demand; all three fans will operate in high
speed with a Y2 demand.
Both low and high voltage plugs are located at the top of the
blower compartment in the indoor section of the unit. Con­
denser fan motors B4, B5 and B21 high voltage plugs are
J86, J87 and J88 respectively. Low voltage plugs are J336,
J337 and J338 respectively. Refer to wiring markings to
identify plugs. Use figure 13 to identify fan motors.
If an ECM fan is not operating:
1 Check to make sure high voltage is present before
checking low voltage.
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