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System Operation
UNIT COMPONENTS
IMPORTANT
Some scroll compressors have an internal vacuum
protector that will unload scrolls when suction pressure
goes below 20 psig. A hissing sound will be heard when
the compressor is running unloaded. Protector will
reset when low pressure in system rises above 40 psig.
DO NOT REPLACE COMPRESSOR.
The outdoor unit and indoor blower cycle on demand from
the room thermostat. If the thermostat blower switch is in
the
ON
position, the indoor blower operates continuously.
Liquid line Filter Drier
The unit is equipped with a large-capacity filter drier which
keeps the system clean and dry. If replacement is neces
-
sary, order another of the same design and capacity. The
replacement filter drier must be suitable for use with HFC-
410A refrigerant.
Low Pressure Switch (S87)
The ML18XC2 is equipped with an auto-reset low pres-
sure switch which is located on the vapor line. The switch
shuts off the compressor when the vapor pressure falls
below the factory setting. This switch, which is ignored
during defrost operation, closes at pressures at or above
40 ± 5 psig (276 ± 34 kPa) and opens at 25 ± 5 psig (172
± 34 kPa). It is not adjustable.
High Pressure Switch (S4)
The ML18XC2 is equipped with an auto-reset high pres-
sure switch (single-pole, single-throw) which is located on
the liquid line. The switch shuts off the compressor when
discharge pressure rises above the factory setting. The
switch is normally closed and is permanently adjusted to
trip (open) at 590 ± 15 psig (4068 ± 103 kPa).
NOTE
–
A Schrader core is under the pressure switches.
Crankcase Heater (HR1) and Thermostat Switch (S40)
All models sizes are equipped with a belly band type
crankcase heater. HR1 prevents liquid from accumulating
in the compressor. The HR1 is controlled by a single pole,
single throw thermostat switch (S40) located on the liquid
line. On all units, the heater is on when there is no com
-
pressor operation.
Thermal Protection Switch (S173) – Compressor
Mounted
Some ML18XC2 units are equipped with a compressor
mounted normally closed temperature switch that pre
-
vents compressor damage due to overheating caused
by internal friction. The switch is located on top of the
compressor casing (see figure 1). This switch senses
the compressor casing temperature and opens at 239-
257°F (115°C-125°C) to shut off compressor operation.
The auto-reset switch closes when the compressor cas-
ing temperature falls to 151-187°F (66°C-86°C), and the
compressor is re-energized. This single-pole, single-throw
(SPST) bi-metallic switch is wired in series with the 24V Y
input signal to control compressor operation.
Maintenance
DEALER
WARNING
Electric Shock Hazard. Can cause injury or
death. Unit must be properly grounded in
accordance with national and local codes.
Line voltage is present at all components
when unit is not in operation on units with
single-pole contactors. Disconnect all remote
electric power supplies before opening
access panel. Unit may have multiple power
supplies.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer or
equivalent, service agency, or the gas supplier.
Maintenance and service must be performed by a quali
-
fied installer or service agency. At the beginning of each
cooling season, the system should be checked as follows:
Outdoor Unit
1 - Clean and inspect outdoor coil (may be flushed with
a water hose). Ensure power is off before cleaning.
2 - Outdoor unit fan motor is pre-lubricated and sealed.
No further lubrication is needed.
3 -
Visually inspect all connecting lines, joints and coils
for evidence of oil leaks.
4 -
Check all wiring for loose connections.
5 -
Check for correct voltage at unit (unit operating).
6 -
Check amp draw on outdoor fan motor.
Motor Nameplate:_________ Actual:__________.
7 -
Inspect drain holes in coil compartment base and
clean if necessary.
NOTE
–
If insufficient cooling occurs, the unit should be
gauged and refrigerant charge should be checked.
Outdoor Coil
It may be necessary to flush the outdoor coil more fre-
quently if it is exposed to substances which are corrosive
or which block airflow across the coil (e.g., pet urine, cot-
tonwood seeds, fertilizers, fluids that may contain high
levels of corrosive chemicals such as salts)
•
Outdoor Coil – The outdoor coil may be flushed with a
water hose.
• Outdoor Coil (Sea Coast) – Moist air in ocean locations
can carry salt, which is corrosive to most metal. Units that
are located near the ocean require frequent inspections
and maintenance. These inspections will determine the
necessary need to wash the unit including the outdoor
coil. Consult your installing contractor for proper intervals/
procedures for your geographic area or service contract.
