Lennox Signature XP19-024 User manual

Page 1 ©2005 Lennox Industries Inc.
Corp. 0510−L4
XP19
Service Literature Revised 06−2008
XP19 SERIES UNITS
The XP19 is a high efficiency residential split−system heat
pump unit, which features a two−step scroll compressor
and R410A refrigerant. XP19 units are available in 2, 3 , 4
and 5 ton sizes. The series is designed for use with an ex-
pansion valve only (approved for use with R410A) in the in-
door unit. This manual is divided into sections which dis-
cuss the major components, refrigerant system, charging
procedure, maintenance and operation sequence.
Information contained in this manual is intended for use by
qualified service technicians only. All specifications are
subject to change.
CAUTION
Physical contact with metal edges and corners while
applying excessive force or rapid motion can result
in personal injury. Be aware of, and use caution when
working nearby these areas during installation or
while servicing this equipment.
CAUTION
To prevent personal injury, or damage to panels, unit
or structure, be sure to observe the following:
While installing or servicing this unit, carefully stow
all removed panels out of the way, so that the panels
will not cause injury to personnel, nor cause damage
to objects or structures nearby, nor will the panels be
subjected to damage (e.g., being bent or scratched).
While handling or stowing the panels, consider any
weather conditions, especially windy conditions,
that may cause panels to be blown around and bat-
tered.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a qualified installer or service
agency.
DANGER
Shock Hazard
Remove all power at disconnect be-
fore removing access panel.
XP19 units use single-pole contac-
tors. Potential exists for electrical
shock resulting in injury or death.
Line voltage exists at all components
(even when unit is not in operation).
Table of Contents
General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications / Electrical Data 2. . . . . . . . . . . . . . . . . .
I Application 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Unit Components 3. . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Refrigerant System 18. . . . . . . . . . . . . . . . . . . . . . . . . .
IV Charging 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V Service and Recovery 24. . . . . . . . . . . . . . . . . . . . . . . .
VI Maintenance 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIIBrazing Procedure 24. . . . . . . . . . . . . . . . . . . . . . . . . .
VIII Diagrams and Operating Sequence 25. . . . . . . . . .

Page 2
SPECIFICATIONS
General
Dt
Model No. XP19−024 XP19−036 XP19−048 XP19−060
Data Nominal Tonnage (kW) 2 (7.0) 3 (10.6) 4 (14.1) 5 (17.6)
Connections
(t)
Liquid line (o.d.) − in. (mm) 3/8 (9.5) 3/8 (9.5) 3/8 (9.5) 3/8 (9.5)
(sweat) Vapor line (o.d.) − in. (mm) 7/8 (22.2) 7/8 (22.2) 7/8 (22.2) 1−1/8 (28.6)
Refrigerant 1R−410A charge furnished 12 lbs. 0 oz. (5.4
kg)
12 lbs. 5 oz. (5.6
kg)
13 lbs. 8 oz. (6.1
kg)
16 lbs. 5 oz. (7.4
kg)
Outdoor
Cil
Net face area − sq. ft. (m2) Outer coil 20.50 (1.90) 20.50 (1.90) 26.92 (2.50) 26.92 (2.50)
Coil Inner coil 19.86 (1.85) 19.86 (1.85) 26.07 (2.42) 26.07 (2.42)
Tube diameter − in. (mm) 5/16 (0.52) 5/16 (0.52) 5/16 (0.52) 5/16 (0.52)
No. of rows 2 2 2 2
Fins per inch (m) 22 (866) 22 (866) 22 (866) 22 (866)
Outdoor
F
Diameter − in. (mm) 26 (660) 26 (660) 26 (660) 26 (660)
Fan No. of blades 3 3 3 3
Motor hp (W) 1/3 (249) 1/3 (249) 1/3 (249) 1/3 (249)
Cfm (L/s) 1st stage 2500 (1180) 2500 (1180) 2800 (1320) 2800 (1320)
2nd stage 2500 (1180) 2800 (1320) 3400 (1605) 3400 (1605)
Rpm − 1st stage 700 700 700 700
2nd stage 700 820 820 820
Watts − 1st stage 70 70 150 150
2nd stage 70 105 220 220
Shipping Data − lbs. (kg) 1 pkg. 304 (138) 315 (143) 352 (160) 387 (176)
ELECTRICAL DATA
Line voltage data − 60hz 208/230V−1ph 208/230V−1ph 208/230V−1ph 208/230V−1ph
3Maximum overcurrent protection (amps) 25 40 50 60
2Minimum circuit ampacity 15.7 23.7 29.3 34.9
Compressor Rated load amps 10.3 16.7 21.2 25.7
p
Locked rotor amps 52 82 96 118
Power factor 0.98 0.98 0.98 0.98
Outdoor Coil
Fan Motor
Full load amps 2.8 2.8 2.8 2.8
OPTIONAL ACCESSORIES − must be ordered extra
Compressor Hard Start Kit 10J42  
p
81J69  
Compressor Low Ambient Cut−Off 45F08    
Freezestat 3/8 in. tubing 93G35    
1/2 in. tubing 39H29    
5/8 in. tubing 50A93    
Indoor Blower Relay 40K58    
Low Ambient Kit 68M04    
Monitor Kit − Service Light 76F53    
Mounting Base 69J07    
Outdoor
Th t t
Thermostat 56A87    
Thermostat
Kit
Mounting Box − US 31461    
Kit
Canada 33A09    
SignatureStattHome Comfort Control 81M28    
Refrigerant
Line Sets
L15−65−15
L15−65−30
L15−65−40
L15−65−50

Field Fabricate 
Time Delay Relay 58M81    
NOTE − Extremes of operating range are plus 10% and minus 5% of line voltage.
1Refrigerant charge sufficient for 15 ft. (4.6 m) length of refrigerant lines.
2Refer to National or Canadian Electrical Code manual to determine wire, fuse and disconnect size requirements.
3HACR type breaker or fuse.

Page 3
I−APPLICATION
All major components (indoor blower and coil) must be
matched according to Lennox recommendations for the
compressor to be covered under warranty. Refer to the En-
gineering Handbook for approved system matchups. A
misapplied system will cause erratic operation and can re-
sult in early compressor failure.
II−Unit Components
Remove 4 screws to
remove panel for
accessing compressor
and controls.
Install by positioning
panel with holes
aligned; install screws
and tighten.
FIGURE 1
Access Panel
Removing Access Panels
Remove and reinstall the access panel as described in fig-
ure 1.
Remove the louvered panels as follows:
1−. Remove 2 screws, allowing the panel to swing open
slightly.
2−. Hold the panel firmly throughout this procedure.
Rotate bottom corner of panel away from hinge corner
post until lower 3 tabs clear the slots (see figure 2, De-
tail B).
3−. Move panel down until lip of upper tab clears the top
slot in corner post (see figure 2, Detail A).
Position and Install PanelPosition the panel almost
parallel with the unit (figure 2, Detail D) with the screw
side" as close to the unit as possible. Then, in a continuous
motion:
Slightly rotate and guide the LIP of top tab inward (figure 2,
Details A and C); then upward into the top slot of the
hinge corner post.
Rotate panel to vertical to fully engage all tabs.
Holding the panel’s hinged side firmly in place, close the
right−hand side of the panel, aligning the screw holes.
When panel is correctly positioned and aligned, insert the
screws and tighten.
Detail A
Detail C
Detail B
FIGURE 2
Removing/Installing Louvered Panels
MAINTAIN MINIMUM PANEL ANGLE (AS CLOSE TO PARALLEL WITH THE UNIT
AS POSSIBLE) WHILE INSTALLING PANEL.
PREFERRED ANGLE
FOR INSTALLATION
Detail D
ROTATE IN THIS DIRECTION;
THEN DOWN TO REMOVE PANEL
SCREW
HOLES
ANGLE MAY BE TOO
EXTREME
HOLD DOOR FIRMLY TO THE HINGED
SIDE TO MAINTAIN
FULLY−ENGAGED TABS
LIP
IMPORTANT! Do not allow panels to hang on unit by top tab. Tab
is for alignment and not designed to support weight of panel.
Panel shown slightly ro-
tated to allow top tab to
exit (or enter) top slot
for removing (or instal-
ling) panel.

Page 4
FIGURE 3
XP19 PARTS ARRANGEMENT
OUTDOOR FAN
COMPRESSOR
CONTACTOR
DEFROST
CONTROL
LSOM
LOW PRESSURE
SWITCH HIGH PRESSURE
SWITCH
DRIER
REVERSING
VALVE
CAPACITOR
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during unit instal-
lation and service to protect the unit’s electronic
controls. Precautions will help to avoid control
exposure to electrostatic discharge by putting
the unit, the control and the technician at the
same electrostatic potential. Neutralize electro-
static charge by touching hand and all tools on an
unpainted unit surface before performing any
service procedure.
A−Two−Stage Scroll Compressor (B1)
The scroll compressor design is simple, efficient and re-
quires few moving parts. A cutaway diagram of the scroll
compressor is shown in figure 1.The scrolls are located in
the top of the compressor can and the motor is located just
below. The oil level is immediately below the motor.
The scroll is a simple compression concept centered
around the unique spiral shape of the scroll and its inherent
properties. Figure 5 shows the basic scroll form. Two iden-
tical scrolls are mated together forming concentric spiral
shapes (figure 6). One scroll remains stationary, while the
other is allowed to orbit" (figure 7). Note that the orbiting
scroll does not rotate or turn but merely orbits" the station-
ary scroll.
FIGURE 4
TWO−STAGE MODULATED SCROLL
slider ring
solenoid actuator coil
FIGURE 5
SCROLL FORM
FIGURE 6
STATIONARY
SCROLL
ORBITING SCROLL
DISCHARGE
SUCTION
CROSS−SECTION OF SCROLLS
TIPS SEALED BY
DISCHARGE PRESSURE
DISCHARGE
PRESSURE
The counterclockwise orbiting scroll draws gas into the out-
er crescent shaped gas pocket created by the two scrolls
(figure 7 − 1). The centrifugal action of the orbiting scroll
seals off the flanks of the scrolls (figure 7 − 2). As the orbiting
motion continues, the gas is forced toward the center of the
scroll and the gas pocket becomes compressed (figure 7
−3). When the compressed gas reaches the center, it is dis-
charged vertically into a chamber and discharge port in the
top of the compressor (figure 7 − 4). The discharge pressure
forcing down on the top scroll helps seal off the upper and
lower edges (tips) of the scrolls (figure 6). During a single or-
bit, several pockets of gas are compressed simultaneously
providing smooth continuous compression.

Page 5
The scroll compressor is tolerant to the effects of liquid re-
turn. If liquid enters the scrolls, the orbiting scroll is allowed
to separate from the stationary scroll. The liquid is worked
toward the center of the scroll and is discharged.
Due to its efficiency, the scroll compressor is capable of
drawing a much deeper vacuum than reciprocating com-
pressors. Deep vacuum operation can cause internal fusite
arcing resulting in damaged internal parts and will result in
compressor failure. This type of damage can be detected
and will result in denial of warranty claims. The scroll com-
pressor can be used to pump down refrigerant as long as
the pressure is not reduced below 7 psig.
NOTE − During operation, the head of a scroll compressor
may be hot since it is in constant contact with discharge
gas.
The scroll compressors in all XP19 model units are de-
signed for use with R410A refrigerant and operation at high
pressures. Compressors are shipped from the factory with
3MA (32MMMA) P.O.E. oil. See electrical section in this
manual for compressor specifications.
TWO−STAGE OPERATION
The two−stage scroll compressor operates like any stan-
dard scroll compressor with the exception the two−stage
compressor modulates between first stage (low capacity
approximately 67%) and second stage (high capacity).
Modulation occurs when gas is bypassed through bypass
ports (figure 8 bypass ports open) in the first suction pock-
et. This bypassing of gas allows the compressor to operate
on first stage (low capacity) if thermostat demand allows.
Indoor thermostat setting will determine first or second
stage operation. The compressor will operate on first−stage
until demand is satisfied or the indoor temperature reaches
the thermostat set point calling for second−stage.
Second−stage (high capacity) is achieved by blocking the
bypass ports (figure 8 bypass ports closed) with a slider
ring. The slider ring begins in the open position and is con-
trolled by a 24VDC internal solenoid. On a Y2 call the inter-
nal solenoid closes the slider ring, blocking the bypass
ports and bringing the compressor to high capacity. Two−
stage modulation can occur during a single thermostat de-
mand as the motor runs continuously while the compressor
modulates from first−stage to second− stage.
FIGURE 7
SCROLL
HOW A SCROLL WORKS
SUCTION SUCTION
SUCTION
MOVEMENT OF ORBIT
STATIONARY SCROLL
ORBITING
CRESCENT
SHAPED GAS
POCKET
HIGH
PRESSURE
GAS
DISCHARGE
POCKET
FLANKS
SEALED BY
CENTRIFUGAL
FORCE
12
34
SUCTION
INTERMEDIATE
PRESSURE
GAS
SUCTION
POCKET

Page 6
FIGURE 8
Bypass Ports
Closed
High Capacity
Bypass Ports
Open
Low Capacity
TWO−STAGE MODULATION
INTERNAL SOLENOID (L34)
The internal unloader solenoid controls the two−stage op-
eration of the compressor by shifting a slide ring mecha-
nism to open (low capacity) or close (high capacity), two
by−pass ports in the first compression pocket of the scrolls
in the compressor. The internal solenoid is activated by a
24 volt direct current solenoid coil. The internal wires
from the solenoid in the compressor are routed to a 2 pin
fusite connection on the side of the compressor shell. The
external electrical connection is made to the compressor
with a molded plug assembly. The molded plug receives 24
volt DC power from the LSOM II.
If it is suspected the unloader is not operating properly,
check the following
IMPORTANT
This performance check is ONLY valid on systems
that have clean indoor and outdoor coils, proper air-
flow over coils, and correct system refrigerant
charge. All components in the system must be func-
tioning proper to correctly perform compressor
modulation operational check. (Accurate measure-
ments are critical to this test as indoor system load-
ing and outdoor ambient can affect variations be-
tween low and high capacity readings).
STEP 1 Confirm low to high capacity compressor
operation
Tools required
Refrigeration gauge set
Digital volt/amp meter
Electronic temperature thermometer
On-off toggle switch
Procedure
1−. Turn main power "OFF" to outdoor unit.
2−. Adjust room thermostat set point above (heating op-
eration on heat pump) or below (cooling operation) the
room temperature 5ºF.
3−. Remove control access panel. Install refrigeration
gauges on unit. Attach the amp meter to the common
(black wire) wire of the compressor harness. Attach
thermometer to discharge line as close as possible to
the compressor.
4−. Turn toggle switch "OFF" and install switch in series
with Y2 wire from room thermostat.
5−. Cycle main power "ON."
6−. Allow pressures and temperatures to stabilize before
taking any measured reading (may take up to 10 min-
utes).
NOTE − Block outdoor coil to maintain a minimum of 375
psig during testing).
7−. Record all of the readings for the Y1 demand on table
1.
8−. Close switch to energize Y2 demand.
9−. Allow pressures and temperatures to stabilize before
taking any measured reading (this may take up to 10
minutes).
10−.Record all of the readings of Y2 demand on table 1.
NOTE − On new installations or installations that have
shut down for an extended period of time, if the com-
pressor does not cycle from low stage to high stage on
the first attempt, it may be necessary to recycle the com-
pressor back down to low stage and back up to high
stage a few times in order to get the bypass seals to
properly seat
Compare Y1 readings with Y2 readings in table 1. Some
readings should be higher, lower or the same. If the
readings follow what table 1 specifies, the compressor is
operating and shifting to high capacity as designed. If the
readings do not follow what table1 specifies, continue to
step 2 to determine if problem is with external solenoid
plug power.

Page 7
TABLE 1
Compressor Operation
Unit Readings
Y1 −
1st-Stage Expected Results
Y2 −
2nd-Stage
Compressor
Voltage Same
Amperage Higher
Condenser Fan motor
Amperage Same or Higher
Temperature
Ambient Same
Outdoor Coil Discharge Air Higher in Cooling
Lower in Heating
Compressor Discharge Line Higher
Indoor Return Air Same
Indoor Coil Discharge Air Lower in Cooling
Higher in Heating
Pressures
Suction (Vapor) Lower
Liquid Higher
STEP 2 Confirm DC voltage output on compressor
solenoid plug
1−. Shut power off to the outdoor unit.
2−. Insert lead wires from voltmeter into back of the red
and black wire plug jack that feeds power to compres-
sor solenoid coil. Set voltmeter to DC volt scale to read
DC voltage output from LSOM II plug. See figure 9.
FIGURE 9
3−. Apply a Y1 and Y2 demand from the indoor thermostat
to the LSOM II.
4−. Turn power back on to unit.
5−. Compressor should cycle ON" when Y1 is calling.
6−. With Y2 calling, 5 seconds after compressor cycles
ON", LSOM II will output 24 volt DC signal to the com-
pressor solenoid plug. Once the solenoid has pulled in,
the LSOM II will reduce the DC voltage to a pulsating
6 to 18 volt DC output to the solenoid to allow the sole-
noid to remain energized.
IMPORTANT
When checking compressor for two−stage operation,
always cycle Y1 to Y2 from terminals on the LSOMII
or room thermostat connections. DO NOT cycle sec-
ond stage (Y2) of compressor by unplugging the
24VDC solenoid LSOM II end of plug. The LSOM II will
only output a 6 to 18VDC signal which will be insuffi-
cient voltage to pull the solenoid coil in for second
stage.
If compressor solenoid is still not shifting to high capac-
ity, this check will verify that DC power is being fed from
the LSOM II.
7−. Shut power off to unit (main and low voltage)
8−. Unplug the 2 pin solenoid plug from the fusite connec-
tion on the compressor and the plug end from the
LSOM II.
9−. Using an OHM meter, check for continuity on the plug
harness wire ends (red to red, black to black). Wires
should have continuity between same colors and no
continuity between opposite color wires.
If the above checks verify that the solenoid plug is pro-
viding power to cycle into high capacity operation, con-
tinue to step 3 to determine if problem is with solenoid
coil in compressor
STEP 3 Confirm internal unloader solenoid has
proper resistance
1−. Shut all power off to unit (main and low voltage)
2−. Unplug the molded plug from the compressor solenoid
2−pin fusite.
3−. Using a volt meter set on the 200 ohm scale
Replace the Compressor under these conditions:

Page 8
Bad Solenoid
a. Measure the resistance at the 2−pin fusite. The resist-
ance should be 32 to 60 ohms depending on compressor
temperature. If no resistance replace compressor.
b. Measure the resistance from each fusite pin to
ground. There should not be continuity to ground. If so-
lenoid coil is grounded, replace compressor.
Good Solenoid
a. Seals not shifting, replace compressor
b. Slider ring not shifting, replace compressor.
B−Contactor (K1)
The compressor is energized by a contactor located in the
control box. All XP19 units are single phase and use single−
pole contactors.
C−Low Pressure Switch (S87)
The XP19 is equipped with an auto−reset low pressure
switch which is located on the suction line. The switch shuts
off the compressor when the suction pressure falls below
the factory setting. This switch is ignored during the first 90
seconds of compressor start up, during defrost operation,
90 seconds after defrost operation, during test mode and
when the outdoor temperature drops below 15°F.
The switch closes when it is exposed to 55 psig and opens
at 25 psig. It is not adjustable.
D−High Pressure Switch (S4)
IMPORTANT
Pressure switch settings for R410A refrigerant will
be significantly higher than units with R22.
An auto-reset, single-pole/single-throw high pressure switch
is located in the liquid line. This switch shuts off the compres-
sor when liquid line pressure rises above the factory setting.
The switch is normally closed and is permanently adjusted to
trip (open) at 590 + 15 psi and close at 418 + 15 psi. See fig-
ure 3 for switch location.
E−Capacitor (C12)
The compressor in XP19−024, −036, −048 and −060 units
use a permanent split capacitor (see unit wiring diagram).
The capacitor is located inside the unit control box. Ratings
are on capacitor side.
F−Condenser Fan with
Variable Speed Motor(B4)
The variable speed condenser fan motor (figure 10) used in all
units is a three-phase, electronically controlled d.c. brushless
motor (controller converts single phase a.c. to three phase
d.c.), with a permanent-magnet-type rotor, manufactured by
GE. Because this motor has a permanent magnet rotor it does
not need brushes like conventional D.C. motors. The motors
consist of a control module and motor . Internal components
are shown in figure 11. The stator windings are split into three
poles which are electrically connected to the controller. This ar-
rangement allows motor windings to be turned on and off in
sequence by the controller.
The controller is primarily an a.c. to d.c. converter. Con-
verted d.c. power is used to drive the motor. The control-
ler contains a microprocessor which monitors varying
conditions inside the motor (such as motor workload).
The controller uses sensing devices to know what position
the rotor is in at any given time. By sensing the position of
the rotor and then switching the motor windings on and off
in sequence, the rotor shaft turns the blower.
VARIABLE SPEED CONDENSER FAN MOTOR
FIGURE 10
RED
YELLOW
BLACK
RED
BLUE
motor
control module
BLOWER MOTOR COMPONENTS
FIGURE 11
STATOR
(WINDINGS)
OUTPUT
SHAFT
BEARING
ROTOR
Internal Operation
The condenser fan motor is a variable speed motor with RPM
settings at 700 (Y1) and 820 (Y2). The variation in speed is
accomplished each time the controller switches a stator wind-
ing (figure10) on and off, it is called a pulse." The length of
time each pulse stays on is called the pulse width." By vary-
ing the pulse width the controller varies motor speed (called
pulse-width modulation"). This allows for precise control of
motor speed and allows the motor to compensate for varying
load conditions as sensed by the controller. In this case, the
controller monitors the static workload on the motor and var-
ies motor rpm in order to maintain constant airflow (cfm).
Motor rpm is continually adjusted internally to maintain
constant static pressure against the fan blade. The control-
ler monitors the static work load on the motor and motor
amp-draw to determine the amount of rpm adjustment.
Blower rpm is adjusted internally to maintain a constant
cfm. The amount of adjustment is determined by the incre-
mental taps which are used and the amount of motor load-
ing sensed internally. The motor constantly adjusts rpm to
maintain a specified cfm.

Page 9
Initial Power Up
When line voltage is applied to the motor, there will be a
large inrush of power lasting less than 1/4 second. This in-
rush charges a bank of DC filter capacitors inside the con-
troller. If the disconnect switch is bounced when the discon-
nect is closed, the disconnect contacts may become
welded. Try not to bounce the disconnect switch when ap-
plying power to the unit.
The DC filter capacitors inside the controller are connected
electrically to the speed tap wires. The capacitors take
approximately 5 minutes to discharge when the disconnect
is opened. For this reason it is necessary to wait at least 5
minutes after turning off power to the unit before attempting
to service motor.
DANGER
Disconnect power from unit and wait at
least five minutes to allow capacitors
to discharge before attempting to ser-
vice motor. Failure to wait may cause
personal injury or death.
Motor Start-Up
At start-up, the motor may gently rock back and forth for a
moment. This is normal. During this time the electronic
controller is determining the exact position of the rotor.
Once the motor begins turning, the controller slowly
eases the motor up to speed (this is called soft-start").
The motor may take as long as 10-15 seconds to reach
full speed. If the motor does not reach 200rpm within 13
seconds, the motor shuts down. Then the motor will im-
mediately attempt a restart. The shutdown feature pro-
vides protection in case of a frozen bearing or blocked
fan blade. The motor may attempt to start eight times. If
the motor does not start after the eighth try, the controller
locks out. Reset controller by momentarily turning off
power to unit.
Troubleshooting
If first or second stage thermostat call for cool is present
and the variable speed condenser fan motor does not ener-
gize, check voltage at the breaker box. If voltage is present
do the following and reference figure 12.
1− Check for 240 volts between the compressor RED wi-
res.
2− Initiate a first stage call for cool. Check for 24 volts be-
tween the fan motor YELLOW wire and fan motor
BLACK wire.
3− Initiate a second stage call for cool. Check for 24 volts
between the fan motor YELLOW wire and fan motor
BLACK wire, then check for 24 volts between the fan
motor BLUE wire and fan motor BLACK.
4− Repeat steps 1 and 2 with a HEAT call.
FIGURE 12
RED
RED
240V
YELLOW
BLUE
BLACK
common
1st Stage (low capacity − 700 rpm)
2nd Stage (High capacity − 820 rpm)
B4
24V
Y1
Y2
RED
RED
YELLOW
BLUE
BLACK
B4
240V
24V
common
Y2
Y1
24V
0V
24V
24V
240V
240V

Page 10
Replacement
See figure 13 if condenser fan motor replacement is nec-
essary.
FIGURE 13
A" See Table 2
TABLE 2
XP19 UNIT "A" DIM. +1/8"
−024, −036 3/4"
−048, −060 Flush
G−Filter Drier
A filter drier designed for all XP19 model units is factory
installed in the liquid line. The filter drier is designed to re-
move moisture and foreign matter, which can lead to com-
pressor failure.
Moisture and / or Acid Check
Because POE oils absorb moisture, the dryness of the
system must be verified any time the refrigerant sys-
tem is exposed to open air. Acompressor oil sample
must be taken to determine if excessive moisture has been
introduced to the oil. Table 3 lists kits available from Lennox
to check POE oils.
If oil sample taken from a system that has been exposed to
open air does not test in the dry color range, the filter drier
MUST be replaced.
IMPORTANT
Replacement filter drier MUST be approved for
R410A refrigerant and POE application.
Foreign Matter Check
It is recommended that a liquid line filter drier be replaced
when the pressure drop across the filter drier is greater
than 4 psig.
H−Accumulator (XP19−060−1 and −2 only)
5 ton XP19−1 and −2 units are equipped with an accumula-
tor. The purpose of the accumulator is to trap and evapo-
rate all liquid refrigerant returning to the compressor.
TABLE 3
KIT CONTENTS TUBE SHELF LIFE
10N46 − Refrigerant Analysis Checkmate−RT700
10N45 − Acid Test Tubes Checkmate−RT750A (three pack) 2 − 3 years @ room temperature. 3+ years
refrigerated
10N44 − Moisture Test Tubes Checkmate − RT751 Tubes (three pack) 6 − 12 months @ room temperature. 2 years
refrigerated
74N40 − Easy Oil Test Tubes Checkmate − RT752C Tubes (three pack) 2 − 3 years @ room temperature. 3+ years
refrigerated
74N39 − Acid Test Kit Sporlan One Shot − TA−1

Page 11
I−Lennox System Operation Monitor (A132)
The Lennox system operation monitor (LSOM) is a 24 volt
powered module, (see diagnostic module A132 on wiring
diagram and figure 14) wired directly to the indoor unit. The
LSOM is located in the control box and is used to trouble
shoot problems in the system. The module has three LED’s
for troubleshooting: GREEN indicates power status, YEL-
LOW indicates an abnormal condition and RED indicates
thermostat demand, but compressor not operating. See
table 4 for troubleshooting codes.
The diagnostic indicator detects the most common fault
conditions in the heat pump system. When an abnormal
condition is detected, the module communicates the spe-
cific condition through its ALERT and TRIP lights. The
module is capable of detecting both mechanical and elec-
trical system problems. See figure 14 for the system opera-
tion monitor.
FIGURE 14
Lennox System Operation Monitor
DATA OUTPUT
CONNECTOR
.25" SPADE
CONNECTOR (5)
SOLENOID
CONNECTOR
POWER LED
Y2
Y
L
R
C
ALERT LED
TRIP LED
IMPORTANT − The LSOM is not a safety component
and cannot shutdown or control the XP19. The LSOM
is a monitoring device only.
LED Functions
Alert LED (green) − Indicates voltage within the range of
19−28VAC is present at the system monitor connections.
Alert LED (yellow) − communicates an abnormal system
condition through a unique Flash Code the alert LED
flashes a number of times consecutively; then pauses;
then repeats the process. This consecutive flashing corre-
lates 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.
Flash code number − corresponds to a number of LED
flashes, followed by a pause, and then repeated.
Trip & Alert LEDs flashing simultaneously − indicates that
the control circuit voltage is too low for operation. Reset
ALERT flash code by removing 24VAC power from moni-
tor. Last ALERT flash code will display for 1 minute after
monitor is powered on.
Thermostat Second-Stage Cooling
The Lennox system operation monitor (LSOM) requires a
two-stage room thermostat to operate properly.
Y2 room thermostat connectionWhile the compressor
is not running, LSOM will not power the solenoid, re-
gardless of the state of Y2. If alert codes 1 or 9 (see
table 4) appear while the compressor is running,
LSOM will turn off the solenoid to prevent solenoid
damage from overheating conditions.
L terminal connectionThe L connection is used to com-
municate alert codes to the room thermostat. On se-
lected Lennox SignatureStatthermostats, a blinking
check" LED will display on the room thermostat and on
select White-Rodgers room thermostats, an icon on
the display will flash. Either will flash at the same rate
as the LSOM yellow alert LED.
NOTE − ROOM THERMOSTAT WITH SERVICE OR
CHECK LIGHT FEATURE − The room thermostat may
blink the Check" or Service" LED or it may come on
solid. Confirm fault by observing and interpreting the
code from the LSOM yellow alert LED at the unit.
Y2 DC Solenoid Connector (DC SOL)The 24VDC so-
lenoid, which is internal to the compressor, will not op-
erate properly if 24VAC is applied to the compressor
solenoid terminals. A voltmeter attached to the
DCSOL output will measure 4−18 VDC when the sole-
noid is be energized.
Installation verification-LSOMTo verify correct LSOM
installation, two functional tests can be performed. Dis-
connect power from the compressor and force a ther-
mostat call for cooling. The red trip LED should turn on
indicating a compressor trip as long as 24VAC is mea-
sured at the Y terminal. If the red LED does not function
as described, refer to table 4 to verify the wiring. Dis-
connect power from the compressor and 24VAC power
from LSOM. Remove the wire from the Y terminal of
LSOM and reapply power to the compressor, allowing
the compressor to run. The yellow alert LED will begin
flashing a code 8 indicating a welded contactor. Dis-
connect power from the compressor and 24VAC power
from the LSOM. While the LSOM is off, reattach the
wire to the Y terminal. Reapply power to the compres-
sor and 24VAC power to the LSOM; the yellow alert
LED will flash the previous code 8 for one minute and
then turn off. If the yellow LED does not function as de-
scribed, refer to table 4 to verify the wiring.
Resetting alert codesAlert codes can be reset manual-
ly or automatically:
Manual reset: Cycle the 24VAC power to LSOM off and on.
Automatic reset: After an alert is detected, the LSOM con-
tinues to monitor the compressor and system. When/if
conditions return to normal, the alert code is turned off
automatically.

Page 12
TABLE 4
System Operation Monitor LED Troubleshooting Codes
Status LED Condition Status LED Description Status LED Troubleshooting Information
Green Power" LED ON Module has power 24VAC control power is present at the module terminal.
Green Power" LED
OFF
Module not powering up Determine/verify that both R and C module terminals are connected
and voltage is present at both terminals.
Red Trip" LED ON System and compressor
check out OK
1Verify Y terminal is connected to 24VAC at contactor coil.
2Verify voltage at contactor coil falls below 0.5VAC when off.
3Verify 24VAC is present across Y and C when thermostat demand
signal is present; if not present, Y and C wires are reversed.
Thermostat demand signal
Y1 is present, but compres-
sor not running
NOTE − During 5-minute
delay in defrost board, the
red trip" LED will be on.
1Compressor protector is open.
2Outdoor unit power disconnect is open.
3Compressor circuit breaker or fuse(s) is open.
4Broken wire or connector is not making contact.
5Low pressure switch open if present in the system.
6Compressor contactor has failed to close.
Red Trip" & Yellow
Alert" LEDs Flashing Simultaneous flashing. Indicates that the control circuit voltage is too low for operation.
Yellow Alert" Flash
Code 1*
Long Run Time − Compres-
sor is running extremely
long run cycles
1Low refrigerant charge.
2Evaporator blower is not running.
3Evaporator coil is frozen.
4Faulty metering device.
5Condenser coil is dirty.
6Liquid line restriction (filter drier blocked if present).
7Thermostat is malfunctioning.
Yellow Alert" Flash
Code 2*
System Pressure Trip or
Discharge Sensor Fault −
Discharge or suction pres-
sure out of limits or
compressor overloaded
1Check high head pressure or discharge line sensor.
2Condenser coil poor air circulation (dirty, blocked, damaged).
3Condenser fan is not running.
4Return air duct has substantial leakage.
5If low pressure switch is present, see Flash Code 1 information.
Yellow Alert" Flash
Code 3*
Short Cycling − Compres-
sor is running only briefly
1Thermostat demand signal is intermittent.
2Time delay relay or control board is defective.
3If high pressure switch is present, see Flash Code 2 information.
4If discharge sensor is present, see Flash Code 2 information.
Yellow Alert" Flash
Code 4*
Locked Rotor 1Run capacitor has failed.
2Low line voltage (contact utility if voltage at disconnect is low).
3Excessive liquid refrigerant in the compressor.
4Compressor bearings are seized.
Yellow Alert" Flash
Code 5*
Open Circuit 1Outdoor unit power disconnect is open.
2Unit circuit breaker or fuse(s) is open.
3Unit contactor has failed to close.
4High pressure switch is open and requires manual reset.
5Open circuit in compressor supply wiring or connections.
6Unusually long compressor protector reset time due to extreme ambi-
ent temperature.
7Compressor windings are damaged.
Yellow Alert" Flash
Code 6*
Open Start Circuit − Cur-
rent only in run circuit
1Run capacitor has failed.
2Open circuit in compressor start wiring or connections.
3Compressor start winding is damaged.
Yellow Alert" Flash
Code 7*
Open Run Circuit − Current
only in start circuit
1Open circuit in compressor start wiring or connections.
2Compressor start winding is damaged.
Yellow Alert" Flash
Code 8*
Welded Contactor −Com-
pressor always runs
1Compressor contactor failed to open.
2Thermostat demand signal not connected to module.
Yellow Alert" Flash
Code 9*
Low Voltage − Control cir-
cuit <17VAC
1Control circuit transformer is overloaded.
2Low line voltage (contact utility if voltage at disconnect is low).
*Flash code number corresponds to a number of LED flashes, followed by a pause, and then repeated. Reset ALERT flash code
by removing 24VAC power from monitor; last code will display for 1 minute after monitor is powered on.

Page 13
J−Defrost System
The demand defrost controller measures differential tem-
peratures to detect when the system is performing poorly
because of ice build−up on the outdoor coil. The controller
self−calibrates" when the defrost system starts and after
each system defrost cycle. The defrost control board com-
ponents are shown in figure 15.
Defrost Control Board
24V TERMINAL
STRIP
CONNECTIONS
DIAGNOSTIC
LEDS
PRESSURE
SWITCH
CIRCUIT
CONNECTIONS
TEST PINS
Note − Component Locations Vary by Board Manufacturer.
SENSOR PLUG IN
(COIL, AMBIENT,
& DISCHARGE-
SENSORS)
FIGURE 15
REVERSING
VALVE
DELAY
PINS
LOW
AMBIENT
THERMOSTAT
PINS
DEFROST
TERMINATION
PIN SETTINGS
The control monitors ambient temperature, outdoor coil
temperature, and total run time to determine when a de-
frost cycle is required. The coil temperature probe is de-
signed with a spring clip to allow mounting to the outside
coil tubing. The location of the coil sensor is important for
proper defrost operation.
NOTE − The demand defrost board accurately measures
the performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates on
the outdoor coil before the board initiates defrost cycles.
Diagnostic LEDs
The state (Off, On, Flashing) of two LEDs on the defrost
board (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 6.
Defrost Board Pressure Switch Connections
The unit’s automatic reset pressure switches (LO PS − S87
and HI PS − S4) are factory−wired into the defrost board on
the LO−PS and HI−PS terminals, respectively.
Low Pressure Switch (LO−PS)When the low pressure
switch trips, the defrost board will cycle off the compressor,
and the strike counter in the board will count one strike. The
low pressure switch is ignored under the following condi-
tions:
during the defrost cycle and 90 seconds after the termina-
tion of defrost
when the average ambient sensor temperature is below
15° F (−9°C)
for 90 seconds following the start up of the compressor
during "test" mode
High Pressure Switch (HI−PS)When the high pressure
switch trips, the defrost board will cycle off the compressor,
and the strike counter in the board will count one strike.
Defrost Board Pressure Switch Settings
High Pressure (auto reset) − trip at 590 psig; reset at 418
psig.
Low Pressure (auto reset) − trip at 25 psig; reset at 40 psig.
5−Strike Lockout Feature
The internal control logic of the board counts the pressure
switch trips only while the Y1 (Input) line is active. If a pres-
sure switch opens and closes four times during a Y1 (In-
put), the control logic will reset the pressure switch trip
counter to zero at the end of the Y1 (Input). If the pressure
switch opens for a fifth time during the current Y1 (Input),
the control will enter a lockout condition.
The 5−strike pressure switch lockout condition can be reset
by cycling OFF the 24−volt power to the control board or by
shorting the TEST pins between 1 and 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while the Y1 Out line is engaged,
a 5−minute short cycle will occur after the switch closes.
Defrost System Sensors
Sensors connect to the defrost board through a field-re-
placeable harness assembly that plugs into the board.
Through the sensors, the board detects outdoor ambient,
coil, and discharge temperature fault conditions. As the de-
tected temperature changes, the resistance across the
sensor changes. Sensor resistance values can be checked
by ohming across pins shown in table 5. The graph in figure
16 shows sensor temperature to resistance range.
NOTE − When checking the ohms across a sensor, be
aware that a sensor showing a resistance value that is not
within the range shown in table 5, may be performing as de-
signed. However, if a shorted or open circuit is detected,
then the sensor may be faulty and the sensor harness will
need to be replaced.
TABLE 5
Sensor Temperature / Resistance Range
Sensor
Temperature
Range °F (°C)
Resistance values
range (ohms)
Pins/Wire
Color
Outdoor −35 (−37) to 120
(48)
280,000 to 3750 3 & 4
(Black)
Coil −35 (−37) to 120
(48)
280,000 to 3750 5 & 6
(Brown)
Discharge (if
applicable)
24 (−4) to 350
(176)
41,000 to 103 1 & 2
(Yellow)
Note: Sensor resistance increases as sensed temperature decreases.

Page 14
Ambient and Coil Sensor Discharge Sensor
RESISTANCE (OHMS) RESISTANCE (OHMS)
TEMPERATURE (ºF) TEMPERATURE (ºF)
5750
7450
9275
11775
15425
19975
26200
34375
46275
62700
200
325
250
425
600
825
1175
1700
2500
3750
5825
100
90
80
70
60
50
40
30
20
10
0
300
280
260
240
220
200
180
160
140
120
100
10000 30000 50000 70000 90000 1000 2000 50004000 60003000
4650
3000
2025
1400
1000
700
225
275
375
500
85300
FIGURE 16
FIGURE 17
Sensor Locations
24 tubes up
(after April
2006)
SLEEVE
AMBIENT SENSOR − Extend
tip of plastic sensor just
outside of plastic sleeve.
Place ambient sensor and wire
from defrost board inside of
plastic sleeve and route thru
gap between corner post and
coil support as shown. Secure
with wire tie.
DISCHARGE SENSOR
WIRE TIE
COIL SENSOR −
Clip coil temperature sensor from the defrost board
on the return bend shown on models as follows:
Model −024 & −036: 12 tubes up from bottom (11−1/2");
Model −048 & −060 (before April 2006): 16 tubes up from bottom (15−1/2")
Model −048 & −060 (after April 2006): 24 tubes up from bottom (23−1/2")
Models −024 & −036 Models −048 & −060
16 tubes
up (before
April 2006)
12 tubes up
Ambient SensorThe ambient sensor (shown in detail A,
figure 17) considers outdoor temperatures below −35°F
(−37°C) or above 120°F (48°C) as a problem. If the ambient
sensor is detected as being open, shorted or out of the tem-
perature range of the sensor, the board will not perform de-
mand defrost operation. The board will revert to time/tem-
perature defrost operation and will display the appropriate
fault code. Heating and cooling operation will be allowed in
this fault condition.
Coil SensorThe coil temperature sensor (shown in de-
tail B, figure 17) considers outdoor temperatures below
−35°F (−37°C) or above 120°F (48°C) as a problem. If the
coil temperature sensor is detected as being open, shorted
or out of the temperature range of the sensor, the board will
not perform demand or time/temperature defrost operation
and will display the appropriate fault code. Heating and
cooling operation will be allowed in this fault condition.
Discharge Line SensorIf the discharge line tempera-
ture (shown in figure 17) exceeds a temperature of 285°F
(140°C) during compressor operation, the board will de−en-
ergize the compressor contactor output (and the defrost
output, if active). The compressor will remain off until the
discharge temperature has dropped below 225°F (107°C)
and the 5-minute anti−short cycle delay has been satisfied.
This sensor has two fault and lockout codes:
3−. If the board recognizes five high discharge line temper-
ature faults during a single (Y1) compressor demand,
it reverts to a lockout mode and displays the appropri-
ate code. This code detects shorted sensor or high dis-
charge temperatures. (Code on board is Discharge
Line Temperature Fault and Lockout").

Page 15
4−. If the board recognizes five temperature sensor range
faults during a single (Y1) compressor demand, it re-
verts to a lockout mode and displays the appropriate
code. The board detects open sensor or out-of-tem-
perature sensor range. This fault is detected by allow-
ing the unit to run for 90 seconds before checking sen-
sor resistance. If the sensor resistance is not within
range after 90 seconds, the board will count one fault.
After 5 faults, the board will lockout. (Code on board is
Discharge Sensor Fault and Lockout").
The discharge line sensor, which covers a range of 150°F
(65°C) to 350°F (176°C), is designed to mount on a ½" re-
frigerant discharge line.
NOTE − Within a single room thermostat demand, if
5−strikes occur, the board will lockout the unit. Defrost
board 24 volt power R" must be cycled OFF" or the
TEST" pins on board must be shorted between 1 to 2 sec-
onds to reset the board.
Second−Stage OperationIf the board receives a call for
second−stage compressor operation Y2" in heating or
cooling mode and the first-stage compressor output is ac-
tive, the second-stage compressor solenoid output will be
energized by the LSOM.
NOTE − The LSOM has a 5 second delay between Y2 being
powered and the solenoid energizing.
If first-stage compressor output is active in heating mode
and the outdoor ambient temperature is below the selected
compressor lock−in temperature, the second-stage com-
pressor solenoid output will be energized without the Y2"
room thermostat input. If the jumper is not connected to one
of the temperature selection pins on P3 (40, 45, 50, 55°F),
the default lock−in temperature of 40°F (4.5°C) will be used.
The board de−energizes the second-stage compressor so-
lenoid output immediately when the Y2" signal is removed
or the outdoor ambient temperature is 5°F above the se-
lected compressor lock−in temperature, or the first-stage
compressor output is de−energized for any reason.
Defrost Temperature Termination Shunt (Jumper)
PinsThe defrost board selections are: 50, 70, 90, and
100°F (10, 21, 32 and 38°C). The shunt termination pin is
factory set at 50°F (10°C). If the temperature shunt is not
installed, the default termination temperature is 90°F
(32°C).
Delay Mode
The defrost board has a field−selectable function to reduce
occasional sounds that may occur while the unit is cycling
in and out of the defrost mode. When a jumper is installed
on the DELAY pins, the compressor will be cycled off for 30
seconds going in and out of the defrost mode. Units are
shipped with jumper installed on DELAY pins.
NOTE − The 30 second off cycle is NOT functional when
jumpering the TEST pins.
Operational Description
The defrost control board has three basic operational
modes: normal, calibration, and defrost.
Normal ModeThe demand defrost board monitors the O
line, to determine the system operating mode (heat/cool),
outdoor ambient temperature, coil temperature (outdoor
coil) and compressor run time to determine when a defrost
cycle is required.
Calibration ModeThe board is considered uncalibrated
when power is applied to the board, after cool mode opera-
tion, or if the coil temperature exceeds the termination tem-
perature when it is in heat mode.
Calibration of the board occurs after a defrost cycle to en-
sure that there is no ice on the coil. During calibration, the
temperature of both the coil and the ambient sensor are
measured to establish the temperature differential which is
required to allow a defrost cycle. See figure 19 for calibra-
tion mode sequence.
Defrost ModeThe following paragraphs provide a de-
tailed description of the defrost system operation.
Detailed Defrost System Operation
Defrost CyclesThe demand defrost control board initi-
ates a defrost cycle based on either frost detection or time.
Frost DetectionIf the compressor runs longer than 34
minutes and the actual difference between the clear
coil and frosted coil temperatures exceeds the maxi-
mum difference allowed by the control, a defrost cycle
will be initiated.
TimeIf 6 hours of heating mode compressor run time has
elapsed since the last defrost cycle while the coil tem-
perature remains below 35°F (2°C), the demand de-
frost control will initiate a defrost cycle.

Page 16
ActuationWhen the reversing valve is de−energized, the
Y1 circuit is energized, and the coil temperature is below
35°F (2°C), the board logs the compressor run time. If the
board is not calibrated, a defrost cycle will be initiated after
34 minutes of heating mode compressor run time. The con-
trol will attempt to self−calibrate after this (and all other) de-
frost cycle(s).
Calibration success depends on stable system tempera-
tures during the 20−minute calibration period. If the board
fails to calibrate, another defrost cycle will be initiated after
45 minutes (90 minutes for −1 to −4 boards) of heating mode
compressor run time. Once the defrost board is calibrated,
it initiates a demand defrost cycle when the difference be-
tween the clear coil and frosted coil temperatures exceeds
the maximum difference allowed by the control OR after 6
hours of heating mode compressor run time has been
logged since the last defrost cycle.
NOTE − If ambient or coil fault is detected, the board will not
execute the TEST" mode.
TerminationThe defrost cycle ends when the coil tem-
perature exceeds the termination temperature or after 14
minutes of defrost operation. If the defrost is terminated by
the 14−minute timer, another defrost cycle will be initiated
after 34 minutes of run time.
Test ModeWhen Y1 is energized and 24V power is be-
ing applied to the board, a test cycle can be initiated by
placing the termination temperature jumper across the
Test" pins for 2 to 5 seconds. If the jumper remains across
the Test" pins longer than 5 seconds, the control will ignore
the test pins and revert to normal operation. The jumper will
initiate one cycle per test.
Enter the TEST" mode by placing a shunt (jumper) across
the TEST" pins on the board after power−up. (The TEST"
pins are ignored and the test function is locked out if the
shunt is applied on the TEST" pins before power−up).
Board timings are reduced, the low−pressure switch and
loss of charge detection fault is ignored and the board will
clear any active lockout condition.
Each test pin shorting will result in one test event. For
each TEST" the shunt (jumper) must be removed for at
least 1 second and reapplied. Refer to flow chart (figure 18)
for TEST" operation.
Note: The Y1 input must be active (ON) and the O" room
thermostat terminal into board must be inactive.
Defrost Board Diagnostics
See table 6 to determine defrost board operational condi-
tions and to diagnose cause and solution to problems.
If in COOLING Mode If in HEATING Mode If in DEFROST Mode
Short test pins for longer
than 1 second but less than
2.0 seconds
Short test pins for more than 2.0 seconds
Y1 Active (0" line inactive)
FIGURE 18
Test Mode
Test pin short REMAINS in place for more than 5 seconds Test pins short REMOVED before a
maximum of 5 seconds
Clear any short cycle lockout
and 5 strike fault lockout
function, if applicable. No
other functions will be
executed and unit will
continue in the mode it was
operating.
No further test mode
operation will be
executed until the test
short is removed and
reapplied.
The controller will check for
ambient and coil faults (open or
shorted). If a fault exists, the
unit will remain in Heat Mode
and no further test mode
operation will be executed until
the test short is removed and re
applied. If no fault exists, the
unit will go into Defrost mode.
The unit will terminate
defrost and enter Heat
Mode uncalibrated with
defrost timer set for 34
minute test. No further
test mode operation will
be executed until the test
short is removed and
reapplied.
Clear any short cycle lockout and 5 strike
fault lockout function, if applicable.
The unit will return to Heat mode uncalibrated with defrost
timer set for 34 minutes. No further test mode operation will
be executed until the test short is removed and re applied.
The unit will remain in Defrost mode
until termination on time or temperature

Page 17
Calibration Mode Sequence
Occurs after power up, after cooling operation, or if the coil temperature exceeds the termination
temperature while in Heat Mode.
DCB defaults to 34 minutes Time/Temperature Mode
Reset Compressor Runtime / Reset Three / Five Strike Counter
DEMAND MODE
Accumulate compressor run-
time while coil temperature
is below 35° F (2°C). When
the accumulated compres-
sor time exceeds 6 hours or
if the coil sensor indicates
frost is present on coil, go to
Defrost.
34 MIN. TIME/TEMP. MODE
Accumulate compressor run-
time while coil temperature
is below 35° F (2°C). When
the accumulated compressor
time exceeds 34 minutes go
to Defrost.
45 MIN. TIME/TEMP. MODE
(90 min for −1 to −4 boards)
Accumulate compressor run-
time while coil temperature is
below 35° F (2°C). When the
accumulated compressor
time exceeds 90 minutes go
to Defrost.
DEFROST
OUTDOOR FAN Off
Reversing Valve ON
W1 line ON
Monitor coil temperature
and time in defrost mode.
HOW DID DEFROST TERMINATE?
Coil temperature was
above 35°F (2°C) for 4
min. of the 14 min. de-
frost OR reached defrost
termination temp.
DCB’s 60L3901 and 46M8201
LO−PS Termination Option
selected. Defrost terminated by
pressure.
Defrosted for 14 min. with-
out the coil temp. going
above 35°F (2°C) for 4
min and coil did not reach
termination temp.
At termination of defrost the compressor
runtime counter is reset/Turn on Outdoor
FAN /Rev Valve & W1 turn off.
At Termination of Defrost
the compressor runtime
counter is reset/Turn on
Outdoor FAN/Rev valve &
W turn OFF
Attempt to Calibration−Temperature measurements are not taken
for the first few minutes of each heat demand. This is to allow coil
temperatures to stabilize. DCB has a maximum of 20 minutes of
accumulated compressor runtime in heat mode to calibrate DCB
This may involve more than one heating demand.
YES, calibration occurred Was stable coil temp. attained
within 20 minutes?
NO, DCB reverts to 45 min. (90
min. for −1 to −4 boards) time/temp.
FIGURE 19

Page 18
TABLE 6
Defrost Control Board Diagnostic LEDs
DS2
Green
DS1
Red Condition/Code Possible Cause(s) Solution
OFF OFF Power problem No power (24V) to board termi-
nals R & C or board failure.
1Check control transformer power (24V).
2If power is available to board and LED(s) do
not light, replace board.
Simultaneous
SLOW Flash
Normal operation Unit operating normally or in
standby mode.
None required.
Alternating
SLOW Flash
5−minute anti−short cycle
delay
Initial power up, safety trip, end of
room thermostat demand.
None required (Jumper TEST pins to override)
Simultaneous
FAST Flash
Ambient Sensor Problem Sensor being detected open or shorted or out of temperature range. Board will re-
vert to time/temperature defrost operation. (System will still heat or cool).
Alternating
FAST Flash
Coil Sensor Problem Sensor being detected open or shorted or out of temperature range. Board will not
perform demand or time/temperature defrost operation. (System will still heat or
cool).
ON ON Circuit Board Failure Indicates that board has internal component failure. Cycle 24 volt power to board. If
code does not clear, replace board.
FAULT & LOCKOUT CODES (Each fault adds 1 strike to that code’s counter; 5 strikes per code = LOCKOUT)
OFF SLOW
Flash
Low Pressure Fault 1Restricted air flow over indoor
or outdoor coil.
2Improper refrigerant charge in
t
1Remove any blockages or restrictions from
coils and/or fans. Check indoor and outdoor
fan motor for proper current draws.
2Ch k t h i h & b
OFF ON Low Pressure LOCKOUT
pp g g
system.
3Improper metering device
installed or incorrect operation
pp
2Check system charge using approach & sub-
cooling temperatures.
3Check system operating pressures and
SLOW
Flash
OFF High Pressure Fault
i
ns
t
a
ll
e
d
or
i
ncorrec
t
opera
ti
on
of metering device.
4Incorrect or improper sensor
location or connection to sys-
3Ch
ec
k
sys
t
em opera
ti
ng pressures an
d
compare to unit charging charts.
4Make sure all pressure switches and sensors
have secure connections to system to prevent
ON OFF High Pressure LOCKOUT
location
or
connection
to
sys
tem.
have
secure
connections
to
system
to
prevent
refrigerant leaks or errors in pressure and
temperature measurements.
SLOW
Flash
ON Discharge Line Tempera-
ture Fault
This code detects shorted sensor or high discharge temperatures. If the discharge
line temperature exceeds a temperature of 285ºF (140ºC) during compressor op-
eration the board will de
−
energize the compressor contactor output (and the de
-
FAST
Flash
ON Discharge Line Tempera-
ture LOCKOUT
era
ti
on,
th
e
b
oar
d
w
ill
d
e−energ
i
ze
th
e compressor con
t
ac
t
or ou
t
pu
t
(
an
d
th
e
d
e-
frost output if active). The compressor will remain off until the discharge tempera-
ture has dropped below 225ºF (107ºC).
OFF Fast
Flash
Discharge Sensor Fault The board detects open sensor or out of temperature sensor range. This fault is
detected by allowing the unit to run for 90 seconds before checking sensor resist-
ance If the sensor resistance is not within range after 90 seconds the board will
Fast
Flash
OFF Discharge Sensor
LOCKOUT
ance. If the sensor resistance is not within range after 90 seconds, the board will
count one fault. After 5 faults, the board will lockout.

Page 19
K−Crankcase Heater (HR1)
Compressors in all units are equipped with a 70 watt belly-
band type crankcase heater. HR1 prevents liquid from ac-
cumulating in the compressor. HR1 is controlled by the
crankcaseheater thermostat.
L− Crankcase heater Thermostat (S40)
Thermostat S40 controls the crankcase heater in all units.
S40 is located on the liquid line. When liquid line tempera-
ture drops below 50° F the thermostat S40 closes energizing
HR1. The thermostat will open, de−energizing HR1 once liq-
uid line temperature reaches 70° F .
III−REFRIGERANT SYSTEM
IMPORTANT
The Clean Air Act of 1990 bans the intentional vent-
ing of (CFC’s and HFC’s) as of July 1, 1992. Approved
methods of recovery, recycling or reclaiming must
be followed. Fines and/or incarceration my be levied
for noncompliance.
Field refrigerant piping consists of liquid and vapor lines
from the outdoor unit (sweat connections). Use Lennox
L15 series line sets as shown in table 7.
Separate liquid and suction service ports are provided at
the service valves for connection of gauge manifold during
charging procedure. Figure 20 shows XP19 refrigerant
flow and gauge manifold connections.
TABLE 7
Mdl
Valve Field Size
Connections Recommended Line Set
Model
Liquid
Line
Vapor
Line Liquid
Line
Vapor
Line
L15
Line Sets
−024,−
036
3/8 in.
10 mm
7/8 in.
22 mm
3/8 in.
10 mm
7/8 in.
19 mm
L15−65
15 ft. − 50 ft.
4.6 m − 15 m
−048
3/8 in.
10 mm
1−1/8 in.
29 mm
3/8 in.
10 mm
7/8 in.
22 mm
L15−65
15 ft. − 50 ft.
4.6 m − 15 m
−060 3/8 in.
10 mm
1−1/8 in.
29 mm
3/8 in.
10 mm
1−1/8 in.
29 mm
Field
Fabricated
XP19 COOLING CYCLE
(Showing Gauge Manifold Connections)
NOTE−Use gauge ports on vapor line valve and liquid valve for evacuating refrigerant lines
and indoor coil. Use suction gauge port to measure suction pressure during charging.
OUTDOOR
COIL
EXPANSION/
CHECK VALVE
BIFLOW
FILTER / DRIER
TO
R410A
DRUM
LOW
PRESSURE
HIGH
PRESSURE
COMPRESSOR
REVERSING VALVE
VAPOR
LINE
VALVE
MUFFLER
NOTE − ARROWS INDICATE
DIRECTION OF REFRIGERANT FLOW.
REFRIGERANT WILL FLOW IN OPPOSITE
DIRECTION IN HEATING CYCLE.
SERVICE
PORT
SUCTION
EXPANSION/CHECK
VALVE
INDOOR UNIT
OUTDOOR UNIT
LIQUID
LINE
SERVICE
PORT
GAUGE MANIFOLD
DISTRIBUTOR
INDOOR
COIL
FIGURE 20

Page 20
A−Service Valves
Access the liquid line and vapor line service valves (figures
21 and 22) and gauge ports are used for leak testing, eva-
cuating, charging and checking charge. See table 8 for
torque requirements.
Each valve is equipped with a service port which has a fac-
tory−installed Schrader valve. A service port cap protects
the Schrader valve from contamination and serves as the
primary leak seal.
TABLE 8
Part Recommended Torque
Service valve cap 8 ft.− lb. 11 NM
Sheet metal screws 16 in.− lb. 2 NM
Machine screws #10 28 in.− lb. 3 NM
Compressor bolts 90 in.− lb. 10 NM
Gauge port seal cap 8 ft.− lb. 11 NM
IMPORTANT
Service valves are closed to the outdoor unit and
open to line set connections. Do not open the valves
until refrigerant lines have been leak tested and
evacuated. All precautions should be exercised to
keep the system free from dirt, moisture and air.
To Access Schrader Port:
1 − Remove service port cap with an adjustable wrench.
2 − Connect gauge to the service port.
3 − When testing is complete, replace service port cap.
Tighten finger tight, then an additional 1/6 turn.
To Open Service Valve:
1 − Remove stem cap with an adjustable wrench.
2 − Using service wrench and hex head extension, back
the stem out counterclockwise as far as it will go.
NOTE − Use a 3/16" hex head extension for liquid line
size.
3 − Replace stem cap and tighten it firmly. Tighten finger
tight, then tighten an additional 1/6 turn.
To Close Service Valve:
1 − Remove stem cap with an adjustable wrench.
2 − Using service wrench and hex head extension, turn
stem clockwise to seat valve. Tighten it firmly.
NOTE − Use a 3/16" hex head extension for liquid line
size.
3 − Replace stem cap. Tighten finger tight, then tighten an
additional 1/6 turn.
Vapor Line (Ball Type) Valve
Vapor line service valves function the same way as the oth-
er valves, the difference is in the construction. These
valves are not rebuildable. If a valve has failed, you must
replace it. A ball valve valve is illustrated in figure 22.
The ball valve is equipped with a service port with a factory−
installed Schrader valve. A service port cap protects the
Schrader valve from contamination and assures a leak−
free seal.
Front-Seated Liquid Line Service Valve
(Valve Shown
Closed)
Insert hex
wrench here
SCHRADER
VALVE
SERVICE
PORT
To outdoor coil
STEM
CAP
STEM
CAP
(VALVE front-
seated)
To outdoor coil
SCHRADER
VALVE
[open to line set
when valve is
closed (front
seated)]
(Valve Shown Open)
insert hex wrench here
To
indoor coil
SERVICE PORT CAP
SERVICE PORT
SERVICE PORT CAP
To
indoor coil
FIGURE 21
Vapor Line (Ball Type) Service Valve
(Valve Open)
FIGURE 22
BALL
(Shown
closed)
STEM
STEM
CAP
SERVICE
PORT
SCHRADER
VALVE
SERVICE
PORT CAP
To indoor coil
To outdoor coil
Use Adjustable Wrench
To close: rotate Stem
Counter-clockwise 90°.
To open: rotate Stem
Clockwise 90°.