Allied 4SCU18LT Series User manual

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506254-01 Page 1 of 25
Riskofelectricalshock.Disconnectallremote
power supplies before installing or servicing
any portion of the system. Failure to
disconnect power supplies can result in
property damage, personal injury, or death.
WARNING
INSTALLATION AND MAINTENANCE INSTRUCTIONS
4SCU18LT SERIES
Split System Air Conditioner
The equipment covered in this manual is to be installed by trained and experienced service
and installation technicians. Improper installation, modification, service, or use can cause
electricalshock, fire, explosion, or other conditions whichmay cause personal injury,death,
or property damage. Use appropriate safety gear including safety glasses and gloves when
installing this equipment.
WARNING
Installation and servicing of air conditioning
equipment can be hazardous due to internal
refrigerant pressure and live electrical
components.Onlytrainedandqualifiedservice
personnel should install or service this
equipment. Installation and service performed
by unqualified persons can result in property
damage, personal injury, or death.
WARNING
Sharp metal edges can cause injury. When
installing the unit, use care to avoid sharp
edges.
WARNING
TABLE OF CONTENTS
INSTALLATION ...................................... 2
START-UP............................................ 13
OPERATION ........................................ 17
MAINTENANCE ................................... 21
CONNECTION DIAGRAM ................... 23
WARRANTY......................................... 24
ManufacturedBy
AlliedAir Enterprises, Inc.
A Lennox International Inc. Company
215 Metropolitan Drive
West Columbia, SC 29170
*506254-01*
Issue 0912

INSTALLATION When servicing orrepairingHVACcomponents,ensurethe
fastenersareappropriatelytightened. Table 1showstorque
values for fasteners.
Inspection of Shipment
Upon receipt of equipment, carefully inspect it for possible
shipping damage. If damage is found, it should be noted on
the carrier’s freight bill. Take special care to examine the
unitinsidethecartonifthecarton isdamaged.Anyconcealed
damage discovered should be reported to the last carrier
immediately, preferably in writing, and should include a
request for inspection by the carrier’s agent.
If any damages are discovered and reported to the carrier
DO NOT INSTALL THE UNIT, as claim may be denied.
Check the unit rating plate to confirm specifications are
as ordered.
Location of Unit
Outdoor units operate under a wide range of weather
conditions; therefore, multiple factors must be considered
when positioning the unit. The unit must be positioned to
giveadequateclearances for sufficientairflowandservicing.
Refer to Figure 1 for installation clearances.
General
Read this entire instruction manual, as well as the
instructions supplied in separate equipment, before
starting the installation. Observe and follow all
warnings, cautions, instructional labels, and tags.
Failure to comply with these instructions could result
in an unsafe condition and/or premature component
failure.
These instructions are intended as a general guide only for
usebyqualifiedpersonnelanddonotsupersedeanynational
or local codes in any way. The installation must comply with
all provincial, state, and local codes as well as the National
ElectricalCode(U.S.)orCanadianElectricalCode(Canada).
Compliance should be determined prior to installation.
4SCU18LTcondensing units useR410Awhichis anozone-
friendly HFC refrigerant. The unit must be installed with a
matching indoor coil and line set. 4SCU18LT units are
designed for use in expansion valve (TXV) systems only. A
filter drier approved for use with R410A is installed in the
unit.
IMPORTANT: This product has been designed and
manufactured to meet ENERGY STAR criteria for energy
efficiencywhenmatched with appropriate coil components.
However, proper refrigerant charge and proper air flow are
critical to achieve rated capacity and efficiency. Installation
of this product should follow the manufacturer’s refrigerant
chargingandairflowinstructions. Failuretoconfirmproper
charge and airflow may reduce energy efficiency and
shorten equipment life.
Table 1
Fastener Torque
Stem Caps 8 ft. lbs.
Service Port Caps 8 ft. lbs.
Sheet Metal Screws 16 in. lbs.
#8 Machine Screws 16 in. lbs.
#10 Machine Screws 28 in. lbs.
Compressor Bolts 90 in. lbs.
Torque Table
506254-01 Page 2 of 25
Figure 1
Installation Clearances
* A service clearance of 30" must be maintained on one of the
sides adjacent to the control box. Clearance to one of the other
three sides must be 36". Clearance to one of the remaining two
sides may be 12" and the final side may be 6".
A clearance of 24" must be maintained between units.
48" clearance required on top of unit. Maximum soffit overhang is
36".
Issue 0912

Roof Mounting
Install unit at a minimum of 6” above surface of the roof to
avoid ice buildup around the unit. Locate the unit above a
load bearing wall or area of the roof that can adequately
supporttheunit. Consultlocalcodes for rooftopapplications.
Figure 3
• Install the unit high enough above the ground or roof to
allow adequate drainage of defrost water and prevent
ice buildup.
• Inheavysnowareas,donot locate theunitwheredrifting
snowwilloccur. Theunitbaseshouldbe elevated above
the depth of average snows.
NOTE: Elevation of the unit may be accomplished by
construction a frame using suitable materials. If a
support frame is constructed, it must not block drain
holes in unit base.
• Wheninstalledin areas where lowambienttemperatures
exist, locate unit so winter prevailing winds do not blow
directly into outdoor coil.
• Locate unit away from overhanging roof lines which
would allow water or ice to drop on, or in front of, coil or
into unit.
Slab Mounting
When installing a unit at grade level, install on slab high
enough above grade so that water from higher ground will
notcollect aroundthe unit(See Figure2). Slab shouldhave
a slope tolerance away from the building of 2° or 2” per 5’.
Thiswill prevent ice frombuilding up under theunit during a
defrost cycle. Refer to following roof mounting section for
barrierconstruction ifunit must face prevailing winter winds.
If unit coil cannot be mounted away from prevailing winter
winds, a wind barrier should be constructed (See Figure 3).
Size the barrier at least the same height and width as the
outdoor unit. Mount barrier 24” from the sides of the unit in
the direction of the prevailing winds.
Electrical Wiring
Allfield wiring must be done in accordancewith theNational
Electrical Code (NEC) recommendations, Canadian
Electrical Code (CEC) and CSA Standards, or local codes,
whereapplicable.
Refer to the furnace or blower coil installation instructions
for additional wiring application diagrams and refer to unit
rating plate for minimum circuit ampacity and maximum
overcurrent protection size.
WARNING
Unit must be grounded in accordance with national and
local codes. Failure to ground unit properly can result in
personal injury or death.
506254-01 Page 3 of 25
WARNING
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. Failure to disconnect all power supplies could
result in personal injury or death.
Figure 2
Slab Mounting
Issue 0912

Thermostat Designations
See unit wiring diagram for power supply connections.
If the indoor unit is not equipped with a blower relay, one must
be field supplied and installed.
Do not connect C (common) connection between indoor unit
andthermostatexcept whenrequired bytheindoor thermostat.
Refer to thermostat installation instructions. C (common)
connection between indoor unit and outdoor unit required for
proper operation.
Figure 4
Refrigerant Piping
If the 4SCU18LT unit is being installed with a new indoor
coilandline set,the refrigerant connectionsshould bemade
asoutlinedinthis section. If anexistinglineset and/or indoor
coilwill beused tocomplete the system, refer tothis section
as well as the section that follows entitled - Flushing
Existing Line Set and Indoor Coil.
If this unit is being matched with an approved line set or
indoor coil which was previously charged with R-22
refrigerant, the line set and coil must be flushed prior to
installation. Iftheunit is being used withand existingindoor
coilwhich was equipped with a liquid line which served as a
meteringdevice(RFCI),the liquid linemustbereplaced prior
to the installation of the 4SCU18LT unit.
Field refrigerant piping consists of liquid and suction lines
from the outdoor unit (sweat connections) to the indoor coil
(flare or sweat connections).
Select line set diameters from Table 2 to ensure that oil
returns to the compressor. Size vertical suction riser to
maintain minimum velocity at minimum capacity.
Recommended line length is 50’ or less. If more than 50’
line set is required, contact Technical Services. Table 2
showsthediameters forline sets upto 100’althoughvertical
lift applications and trapping requirements need to be
reviewed with Technical Services for line sets over 50’.
Installing Refrigerant Line
During the installation of an air conditioning system, it is
important to properly isolate the refrigerant line to prevent
unnecessary vibration. Line set contact with the structure
(wall, ceiling, or floor) may cause objectionable noise when
vibration is translated into sound. As a result, more energy
or vibration can be expected. Close attention to line set
isolation must be observed.
Following are some points to consider when placing and
installing a high-efficiency outdoor unit:
1. Install line voltage power supply to unit from a properly
sizeddisconnectswitch. Anyexcesshigh voltagefield wiring
should be trimmed or secured away from the low voltage
field wiring.
2.Groundunitatunitdisconnectswitchortoanearthground.
To facilitate conduit, a hole is in the bottom of the control
box. Connect conduit to the control box using a proper
conduit fitting. Units are approved for use only with copper
conductors. 24V Class II circuit connections are made in
the low voltage junction box. Refer to Figure 4 for high
voltagefield wiring diagram. Acomplete unit wiring diagram
is located inside the unit control box cover.
3.Installroomthermostaton an insidewall that isnotsubject
to drafts, direct sunshine, or other heat sources.
4. Install low voltage wiring from outdoor to indoor unit and
from thermostat to indoor unit (See Figure 5).
5. Do not bundle any excess 24V control wire inside control
box. Run control wire through installed wire tie and tighten
wire tie to provide low voltage strain relief and to maintain
seperation of field-installed low and high voltage circuits.
506254-01 Page 4 of 25Issue 0912

Placement
Beawarethatsomelocalitiesareadoptingsound ordinances
based on how noisy the unit is at the neighbor’s home, not
at the original installation. Install the unit as far as possible
fromthe propertyline. When possible, do not installtheunit
directly outside a bedroom window. Glass has a verry high
levelof sound transmission. Figure 5 onpage5 showshow
to place the outdoor unit and line set to reduce line set
vibration.
Line Set Isolation
Illustrations on the pages 6 and 7 demonstrate procedures
which ensure proper refrigerant line set isolation. Figure 6
shows how to install line sets on horizontal runs. Figure 7
shows how to make a transition from horizontal to vertical.
Figure 9 shows how to install line sets on vertical runs.
Brazing Connection Procedure
1. Cut ends of refrigerant lines square (free from nicks or
dents). Debur the ends. The pipe must remain round; do
not pinch end of line.
2. Before making line set connections, use dry nitrogen to
purge the refrigerant piping. This will help to prevent
oxidation and the introduction of moisture into the system.
3. Use silver alloy brazing rods (5% or 6% silver alloy for
copper-to-copper brazing or 45% silver alloy for copper-to-
brass or copper-to-steel brazing) which are rated for use
withR410A refrigerant.
4. Removethe Schradercore assemblies before brazing to
protect them from damage due to extreme heat. Replace
the cores when brazing is complete.
5. Remove light maroon washers from service valves and
shield light maroon stickers to protect them during brazing.
Wrap a wet cloth around the valve body and copper tube
stub to protect it from heat damage.
Figure 5
506254-01 Page 5 of 25Issue 0912
Table 2
Refrigerant Line Set Diameters (in.)
For installations exceeding 50’, contact
Technical Services.
Liquid Line
BTUH Line Set Length and Size
12 ft. 25 ft. 50 ft. 75 ft. 100 ft
.
3/8 3/8 3/8 3/8 3/8
24,000
3/8 3/8 3/8 3/8
3/8 3/8 3/8 1/2
36,000
3/8 3/8 3/8 1/2
48,000
60,000 1/2
1/2
1/2
Suction Line
BTUH Line Set Length and Size
12 ft. 25 ft. 50 ft. 75 ft. 100 ft
.
3/4 3/4
24,000 7/8
36,000
7/8
7/8
7/8
1-1/8
7/8
7/8
1-1/8
48,000
7/87/8
7/8
1-1/8
1-1/8
60,000 1/8 1/8 1-1/8
1-1/8
7/8

Figure 6
6. Brazethe line set to the service valve. Quench the joints
with water or a wet cloth to prevent heat damage to the
valve core and opening port. The tube end must stay
bottomed in the fitting during final assembly to ensure
proper seating, sealing, and rigidity.
7. Install the thermal expansion valve which is sold
separately and which is approved for use with R410A
refrigerantintheliquidlineat the indoorcoil(seeRefrigerant
Metering Device on page 9).
Whenflushing existinglinesetand/orindoorcoil,besureto
empty all existing traps. Residual mineral oil can act as an
insulator, preventing proper heat transfer. It can also clog
thethermalexpansionvalve,reducingsystemperformance
and capacity. Failure to properly flush system as explained
inthese instructions will void warranty.
CAUTION
506254-01 Page 6 of 25Issue 0912

Figure 7
Figure 8
506254-01 Page 7 of 25Issue 0912

Flushing Existing Line Set and Indoor Coil
This procedure should not be performed on systems
which contain contaminants, such as compressor burn
out.
Required Euipment
The following equipment is needed to flush the existing line
setand indoorcoil (See Figure 9). Twoclean R-22recovery
bottles, an oil-less recovery machine with a “pump down”
feature, and two sets of gauges (one for use with R-22 and
one for use with R410A).
Flushing Procedure
IMPORTANT: The line set and/or indoor coil must be
flushed with at least the same amount of refrigerant that
previously charged the system. Check the charge in the
flushing cylinder before flushing the unit.
1. Remove existing R-22 refrigerant using the appropriate
procedure.
Iftheexistingoutdoorunitisnotequippedwithshutoffvalves,
or if the unit is not operational AND the existing R-22
refrigerant will be used to flush the system:
Disconnect all power to the existing outdoor unit. Connect
theexisting unit,a cleanrecovery cylinder, andthe recovery
machine according to the instructions provided with the
recovery machine. Remove all R-22 refrigerant from the
existing system. Refer to the gauges after shutdown to
confirm that the entire system is completely void of
refrigerant. Disconnectthe liquid and suction lines from the
existing outdoor unit.
If the existing outdoor unit is equipped with manual shutoff
valves AND new R-22 refrigerant will be used to flush the
system:
Start the existing R-22 refrigerant system in cooling mode
and close the liquid line valve. Pump all the existing R-22
refrigerant back into the outdoor unit.
(It may be necessary to bypass the low pressure switches
to ensure complete refrigerant evacuation.)
When the low side system pressures reach 0 psig, close
the suction line valve. Disconnect all power to the existing
outdoorunit. Refer to the gaugesafter shutdown toconfirm
that the valves are not allowing refrigerant to flow back into
thelowside of thesystem. Disconnect the liquidandsuction
lines from the existing outdoor unit.
2. Remove the existing outdoor unit. Set the new R410A
unit and follow the brazing connection procedure outlined
previously on this page to make line set connections. Do
not install the R410A thermal expansion valve at this
time.
3. Make low voltage and line voltage connections to the
new outdoor unit. Do not turn on power to the unit or
open the outdoor unit service valves at this time.
Figure 9
506254-01 Page 8 of 25Issue 0912

4. Removerthe existing R-22 refrigerant flowcontrol orifice
or thermal expansion valve before continuing with flushing
procedures. R-22flow control devices are not approved for
usewithR410A refrigerant andmayprevent properflushing.
Use a field-provided fitting to reconnect the lines.
5. Removethepressuretapvalve coresfromthe4SCU18LT
units service valves. Connect an R-22 cylinder with clean
refrigerant to the suction service valve. Connect the R-22
gauge set to the liquid line valve and connect a recovery
maching with an empty recovery tank to the gauge set.
6. Set the recovery machine for liquid recovery and start
the recovery machine. Open the gauge set valves to allow
therecoverymachinetopullavacuumontheexistingsystem
line set and indoor coil.
7. Invert the cylinder of clean R-22 and open its valve to
allow liquid refrigerant to flow in to the system through the
suction line valve. Allow the refrigerant to pass from the
cylinderand throughthe line set and theindoor coil before it
enters the recovery machine.
8. Afteralloftheliquid refrigerant has beenrecovered,switch
the recovery machine to vapor recovery so that all of the R-
22vapor isrecovered. Allow therecovery machineto pulla
vacuum on the sytem.
NOTE: Asinglesystemflushshouldremoveallofthemineral
oilfromtheexistingrefrigerantlinesandindoorcoil. Asecond
flushingmay bedone (using clean refrigerant) if insufficient
amounts of mineral oil were removed during the first flush.
After each system flush, allow the recovery machine to
pulla vacuum on the system at theend of the procedure.
9. Close the valve on the inverted R-22 cylinder and the
gauge set valves. Pump the remaining refrigerant out of
the recovery machine and turn the machine off.
10. Use nitrogen to break the vacuum on the refrigerant
linesand indoor coil before removing the recovery machine,
gauges, and R-22 refrigerant drum. Re-install pressure tap
valve cores into the 4SCU18LT unit’s service valves.
11. Install the fixed orifice (or thermal expansion valve
approvedfor use withR410A refrigerant) in the liquid line at
the indoor coil.
Refrigerant Metering Device
4SCU18LT units are designed for use with TXV systems.
Referto the appropriate following section for information on
installing the chosen refrigerant metering device.
An R410A system will not operate properly with an R-22
metering device.
Install the refrigerant metering device as shown in Figure
10. Do not twist cap tubes when loosening the seal nut
from the orifice housing. Use wrench to back up the
distributor.
Expansion Valve Systems
Expansion valves equipped with Chatleff-type fittings are
available from the manufacturer. See Table 4 for proper
TXV for each unit.
To install an expansion valve (See Figure 10 above):
1. Separatethedistributor assembly and remove the piston
orifice and used teflon seal. Insert nozzle end of the
expansion valve along with a new teflon seal into the
distributorand tighten to20 - 30 ft.lbs. Use backup wrench
on all wrench flats. Overtightening will crush the teflon
seal and may cause a leak.
2. Attach liquid line portion of distributor assembly along
with new teflon seal to the inlet of the expansion valve.
Tighten to 20 - 30 ft. lbs. Use backup wrench on all wrench
flats. Overtightening will crush the teflon seal and may
cause a leak.
Figure 10
506254-01 Page 9 of 25Issue 0912
Table 4
TXV Data
MODEL PART NUMBER
4SCU18LT- 24,-36
4SCU18LT - 48,-60
A4TXV01
A4TXV03

3. Connect the external equalizer line to the equalizer port
on the suction line and tighten to 8 ft.lbs.
4. Strap the superheat sensing bulb to the suction header.
If installing an expansion valve on an indoor coil that
previouslyusedafixedorifice, be suretoremovethe existing
fixedorifice. Failure to remove a fixed orifice wheninstalling
an expansion valve to the indoor coil will result in improper
operation and damage to the system.
Manifold Gauge Set
Manifoldguagesets usedwithsystems charged withR410A
refrigerant must be capable of handling the higher system
operating pressures. The gauges should be rated for use
withpressures 1 - 800 onthe high side and a low side of30”
vacuumto 250psiwith dampened speed to 500 psi. Gauge
hoses must be rated for use at up to 800 psi of pressure
with a 4000 psi burst rating.
Liquid and Suction Line Service Valves
The liquid line and suction line service valves (See Figure
11) and service ports are used for leak teating, evacuation,
charging, and checking charge.
Each valve is equipped with a service port which has a
factory-installedSchrader valve. Aservice port cap protects
the Schrader valve from contamination and serves as the
primary leak seal.
To Access the Schrader Port:
1. Remove the service port cap with an adjustable wrench.
2. Connect gauge to the service port.
3. When testing is completed, replace service port cap.
Tighten finger tight, then an additional 1/6 turn.
To Open Liquid or Suction Line Service Valve:
Remove stem cap with an adjustable wrench.
Use service wrench with a hex-head extension to back the
stem out counterclockwise as far as it will go. Use a 3/16”
hex head extension for liquid line service valves and a 5/
16” extension for suction line service valves.
Replace the stem cap. Tighten finger tight, then tighten an
additional 1/6 turn.
To Close Liquid or Suction Line Service Valve:
1. Remove the stem cap with an adjustable wrench.
2. Use a service wrench with a hex-head extension to turn
the stem clockwise to seat the valve. Tighten firmly.
3. Replace the stem cap. Tighten finger tight, then tighten
an additional 1/6 turn.
Suction Line (Ball Type) Service Valve
Suctionline (ball type)service valvesfunction thesame way
astheother valves;the differenceis inthe construction (See
Figure 12).
Theball valve is equipped with a service port with a factory-
installed Schrader valve. A service port cap protects the
Schrader valve from contamination and serves as the
primary seal.
Leak Testing
After the line set has been connected to the indoor and
outdoor units, the line set connections and indoor unit must
be checked for leaks.
Figure 11
506254-01 Page 10 of 25Issue 0912

Using an Electronic Leak Detector
1. Connect the high pressure hose of the manifold gauge
set to the suction valve service port. (Normally the high
pressure hose is connected to the liquid line port; however,
connectingittothesuctionportshelpstoprotectthemanifold
gauge set from damage caused by high pressure.)
2. Withboth manifoldvalves closed,connect the cylinder of
R410A refrigerant. Open the valve on the R410A cylinder
(vaporonly).
3. Open the high pressure side of the manifold to allow
R410A into the line set and indoor unit. Weigh in a trace
amount of R410A. (A trace amount is a maximum of 2 oz.
of refrigerant or 3 lbs. pressure.) Close the valve on the
R410A cylinder and the valve on the high pressure side of
the manifold gauge set. Disconnect the R410Acylinder.
4. Connecta cylinder of nitrogen witha pressure regulating
valve to the center port of the manifold gauge set. When
using high pressure gas such as nitrogen for this
purpose, be sure to use a regulator that can control the
pressure down to 1 or 2 psig.
5. Adjust nitrogen pressure to 150 psig. Open the valve on
the high side of the manifold gauge set to pressurize the
line set and the indoor coil.
6. After a short period of time, open a refrigerant port to
makesure thatan adequate amount of refrigerant has been
added for detection (refrigerant requirements will vary with
lenths). Checkalljointsforleaks. PurgenitrogenandR410A
mixture. Correct any leaks and rechecks.
Evacuation
Evacuating the system of noncondensables is critical for
proper operation of the unit. Noncondensables are defined
as any gas that will not condense under temperatures and
pressures present during operation of an air conditioning
system. Noncondensables and water vapor combine with
refrigeranttoproducesubstances that corrodecopperpiping
and compressor parts.
Usea thermocoupleor thermistor electronic vacuum gauge
that is calibrated in microns. Use an instrument that reads
down to 50 microns.
1. Connectthemanifold gaugeset to theservice valveports
as follows:
• Low pressure gauge to suction line service valve
• High pressure gauge to liquid line service valve.
2. Connect micron gauge.
3. Connect the vacuum pump (with vacuum gauge) to the
center port of the manifold gauge set.
Figure 12
Refrigerantcan beharmful ifinhaled. Refrigerant must
always be used and recovered responsibly. Incorrect
orirresponsible use of refrigerant can result inpersonal
injury or death.
WARNING
Never use oxygen to pressurize refrigeration or air
conditioning systems. Oxygen will explode on contact
with oil and could cause personal injury or death.
WARNING
Do Not use a compressor to evacuate a system. Avoid
deep vacuum operation. Extremely low vacuums can
cause internal arcing and compressor failure. Danger
ofequipmentdamage. Damagecausedbydeepvacuum
operation will void warranty.
WARNING
506254-01 Page 11 of 25Issue 0912

4. Open both manifold valves and start vacuum pump.
5. Evacuate the line set and indoor unit to a minimum of
500micronsor lower. During the earlystagesofevacuation,
itisdesirable toclosethe manifoldgaugevalve atleastonce
to determine if there is a rapid rise in pressure. Arapid rise
in pressure indicates a relatively large leak. If this occurs,
the leak testing procedure must be repeated.
6. When 500 microns or lower is maintained, close the
manifold gauge valves, turn off the vacuum pump, and
disconnect the manifold gauge center port hose from the
vacuum pump. Attach the manifold gauge center port hose
toa nitrogencylinder with pressure regulator set to 150psig
and purge the hose. Open the manifold gauge valves to
break the vacuum in the line set and indoor unit. Close the
manifold gauge valves.
7. Shut off the nitrogen cylinder and remove the manifold
gauge hose from the cylinder. Open the manifold gauge
valves to release the nitrogen from the line set and indoor
unit.
8. Reconnect the manifold gauge to the vacuum pump,
turn the pump on, and continue to evacuate the line set and
indoorunituntil500 microns ismaintainedwithina20 minute
period after shutting off the vacuum pump and closing the
manifold gauge valves.
9. Whentherequirementsabovehavebeenmet,disconnect
themanifoldhose fromthevacuum pump. Opentheservice
valves to break the vacuum in the line set and indoor unit.
506254-01 Page 12 of 25Issue 0912

START-UP
1. Rotate fan to check for frozen bearings or binding.
2. Inspect all factory and field-installed wiring for loose
connections.
3. Afterevacuationis complete,open liquidline and suction
line service valves to release refrigerant charge (contained
in outdoor unit) into system.
4. Replace the stem caps and secure finger tight, then
tighten an additional 1/6 of a turn.
5. Check voltage supply at the disconnect switch. The
voltagemust be withintherangelistedonthe unit nameplate.
If not, do not start equipment until the power company has
been consulted and the voltage condition corrected.
6. Set thermostat for cooling demand, turn on power to
indoor blower, and close the outdoor unit disconnect switch
to start the unit.
7. Recheck unit voltage with unit running. Power must be
within range shown on unit nameplate.
Refrigerant Charging
This system is charged with R410A refrigerant which
operates at much higher pressures than R-22. The liquid
line drier provided with the unit is approved for use with
R410A. Do not replace it with one designed for use with R-
22. This unit is NOT approved for use with coils which
use capillary tubes as a refrigerant metering device.
R410A refrigerant cylinders are rose colored. Refrigerant
shouldbeadded throughthesuction valveinthe liquidstate.
Certain R410A cylinders are identified as being equipped
with a dip tube. These allow liquid refrigerant to be drawn
fromthe bottom ofthe cylinderwithout invertingthe cylinder.
Do not turn this type of cylinder upside down to draw
refrigerant.
Units are factory charged with the amount of R410A
refrigerant indicated on the unit rating plate. This charge is
based on a matching indoor coil and outdoor coil with 15’
line set. For varying lengths of line set, refer to Table 5 for
refrigerant charge adjustment. A blank space is provided
on the unit rating plate to list the actual field charge.
Table 5
If the system is void of refrigerant, clean the system using
the procedure described below.
1. Use dry nitrogen to pressurized the system and check
for leaks. Repair leaks, if possible.
2. Evacuate the system to remove as much of the moisture
as possible.
3. Use dry nitrogen to break the vacuum.
4. Evacuate the system again.
5. Weighthe appropriateamountofR410Arefrigerant(listed
on unit nameplate) into the system.
6. Monitor the system to determine the amount of moisture
remainingin the oil. Use atest kit to verify that the moisture
content is withing the kit’s dry color range. It may be
necessaryto replace the filter drier several times to achieve
the required dryness level. If system dryness is not
verified, the compressor will fail in the future.
The outdoor unit should be charged during warm weather.
However, applications arise in which charging mustoccur in
the colder months. The method of charging is determined
by the unit’s refrigerant metering device and the outdoor
ambient temperature.
Measuretheliquid line temperatureandthe outdoorambient
temperature as outlined below:
If unit is equipped with a crankcase heater, it should be
energized 24 hours before unit start-up to prevent com-
pressor damage as a result of slugging.
CAUTION
Mineral oils are not compatible with R410A. If oil must
be added, it must be a polyolester oil.
IMPORTANT
Liquid Line Set Diameter
Oz. Per 5 ft. adjust from 15 ft. line set*
3/8 in. 3 oz. Per 5 ft.
* If line length is greater than 15 ft., add this amount.
If line length is less than 15 ft., remove this amount.
Refrigerant ChargeAdjustment
506254-01 Page 13 of 25Issue 0912

5. Comparethesubcooling valuewith those shown inTable
6 on page 14. If subcooling is greater than shown, recover
somerefrigerant. Ifsubcoolingislessthan shown, addsome
refrigerant.
ChargeUsingApproach Method - Outdoor Temperatures
65°F or Above
The following procedure is intended as a general guide and
isforuse onexpansionvalve systemsonly. Forbest results,
indoortemperature shouldbe 70°Fto 80°F. Monitorsystem
pressures while charging.
1. Record outdoor ambient temperature using a digital
thermometer.
2. Attach high pressure gauge set and operate unit for
several minutes to allow system pressures to stabilize.
3. ComparestabilizedpressureswiththoseprovidedinTable
8 on page 15. Minor variations in these pressures may be
expected due to differences in installations. Significant
differences could mean that the system is not properly
charged or that a problem exists with some component
in the system. Pressures higher than those listed indicate
that the system is undercharged. Verify adjusted charge
using the approach method.
4. Use the same digital thermometer to check liquid line
temperature.
5. Subtractthe outdoorambienttemperature fromthe liquid
line temperature to determine the approach temperature.
Blocking Outdoor Coil
Figure 11
506254-01 Page 14 of 25Issue 0912
1. Connectthemanifold gaugeset to theservice valveports
as follows (See Figure 13):
• Low pressure gauge to suction line service valve
• High pressure gauge to liquid line service valve
2. Close manifold gauge set valves. Connect the center
manifold hose to an upright cylinder of R410A.
3. If room temperature is below 70°F, set the room
thermostat to call for heat. This will create the necessary
load for properly charging the system in the cooling cycle.
4. Use a digital thermometer to record the outdoor ambient
temperature.
5. Whenthe heatingdemand has been satisfied, switchthe
thermostat to cooling mode with a set point of 68°F. When
pressures have stabilized, use a digital thermometer to
record the liquid and suction line temperatures.
6. The outdoor temperature will determine which charging
method to use. Proceed with the appropriate charging
method.
Charge Using Subcooling Method - Outdoor
Temperatures Below 65°F
When the outdoor ambient temperature is below 65°F, the
subcooling method can be used to charge the unit. It may
be necessary to restrict the air flow through the outdoor coil
to achieve pressures in the 200-250 psig range. These
higher pressures are necessary for checking the charge.
Block equal sections of air intake panels and move
obstructionssideways until the liquid pressureis in the 200-
250 psig range (see Figure 11).
1. With the manifold gauge hose on the liquid service port
and the unit operating stably, use a digital thermometer to
record the liquid line temperature.
2. Atthe same time, record the liquid line pressure reading.
3. Use the temperature/pressure chart (Table 5 on page
14) to determine the saturation temperature for the liquid
line pressure reading.
4. Subtract the liquid line temperature from the saturation
temperature(accordingtothechart) to determinesubcooling

Table 6
Table 8
R410ATemperature/Pressure Chart
Approach Values for TXV Systems
506254-01 Page 15 of 25Issue 0912
6. Compare the approach value with those shown in Table
7. If thevalues do not agree with those provided inTable 7,
addrefrigeranttolower the approachtemperatureor recover
refrigerant from the system to increase the approach
temperature.
Check Charge Using Normal Operating Pressures
Use Table 8 to perform maintenance checks. Table 8 is not
a procedure for charging the system. Minor variations in
these pressures may be due to differences in installations.
Significant deviations could mean that the system is not
properly charged or that a problem exists with some
component in the system.
Table 7
Subcooling Values

Table 8
Normal Operating Pressures
Low Capacity
24 36 48 60Outdoor Coil
Entering Air
Temp. °F L S L S L S L S
65 205 140 203 139 196 142 236 132
75 247 142 242 141 240 144 278 136
85 288 145 287 144 294 149 321 140
95 330 147 344 147 348 150 363 144
105 372 148 391 149 402 151 405 148
115 413 151 438 153 456 154 447 152
High Capacity
24 36 48 60Outdoor Coil
Entering Air
Temp. °F L S L S L S L S
65 212 137 210 141 237 137 248 123
75 254 139 247 143 286 139 293 128
85 295 142 298 145 330 140 337 132
95 337 144 349 147 374 142 382 137
105 379 146 400 149 418 144 427 142
115 424 149 451 151 462 145 471 146
506254-01 Page 16 of 25Issue 0912

OPERATION
Outdoor unit and indoor blower cycle on demand from the
room thermostat. When the thermostat blower switch is
moved to the ON position, the indoor blower operates
continuously.
System Diagnostic Module
4SCU18LT units contain a diagnostic module for
troubleshooting air conditioning system failures. By
monitoring and analyzing data from the compressor and
thermostat demand, the module can accurately detect the
cause of electrical and system related failure without any
sensors. If a system problem occurs, a flashing LED
indicator communicates the failure code.
LED Description
POWER LED (Green) indicates voltage is present at the
power connection of the module.
ALERT LET (Yellow) communicates an abnormal system
conditionthrough aunique flash code. TheALERTLED will
flash a number of times consecutively, pause, and then
repeat the process. The number of consecutive flashes
correlates to a particular abnormal condition.
TRIP LED (Red) indicates there is a demand signal from
the thermostat but no current to the compressor is detected
by the module. The TRIP LED typically indicates the
compressorprotectorisopen or mayindicatemissingsupply
power to the compressor.
Interpreting the Diagnostic LEDs
Whenan abnormal system condition occurs, the diagnostic
module displays the appropriateALERT and/or TRIP LED.
The yellow ALERT LED will flash a number of times
consecutively, pause, and then repeat the process. To
identify a flash code number, count the number of
consecutiveflashes. Refer toTable 9 onpage 18 andTable
10 on page 19 for information on the flash codes.
Everytime the module powers up,the lastALERTLED flash
code that occurred prior to shutdown is displayed for 60
seconds. The module will continue to display the previous
flash code until the condition returns to normal or 24 VAC is
removedfrom the module. TRIPandALERTLEDsflashing
at the same time means control circuit voltage is too low for
operation.
24 VAC Power Wiring
The diagnoctic module requires a constant nominal 24VAC
powersupply. The wiringto themodule’s R and Cterminals
must be directly from the indoor unit or thermostat.
Thermostat Demand Wiring
Thediagnosticmodule requiresathermostat demandsignal
to operate properly. The thermostat demand signal input,
labeled Y on the module, should always be connected to
the compressor contactor coil so that when the coil is
energized, the demand signal input is 24VAC. When the
Coil is not energized, the demand signal input should be
less than 0.5VAC.
Miswired Module Codes
Dependingon the system configuration, someALERTflash
codes may not be active. The presence of safety switches
affects how the system alerts are displayed by the module.
Miswiringthediagnostic modulewill cause falseLED codes.
Table 11 on page 19 describes LED opeation when the
module is miswired and what troubleshooting action is
required to correct the problem.
506254-01 Page 17 of 25Issue 0912

Table 9
Flash Codes
506254-01 Page 18 of 25Issue 0912

Table 10
Flash Codes (cont.)
506254-01 Page 19 of 25Issue 0912

Table 11
Miswired Module Troubleshooting
506254-01 Page 20 of 25Issue 0912