Lennox 80UHG2-45 Service manual

Page 1  1999 Lennox Industries Inc.
Litho U.S.A.
Corp. 9728−L12
80UHG
Service Literature Revised 01−2002
80UH series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
with tubular heat exchangers formed of aluminized steel.
80UH units are available in heating capacities of 45,000
to 120,000 Btuh and cooling applications up to 5 tons. Refer
to Engineering Handbook for proper sizing.
Units are factory equipped for use with natural gas. Kits are
available for conversion to LP operation. 80UH −1 model
units use electronic (direct spark) ignition. 80UH −2 and −3
model units are equipped with the Lennox SureLight silicon
nitride ignition system. The 80UH X unit meets the Califor
nia Nitrogen Oxides (NOx) Standards and California Sea
sonal Efficiency requirements. All units use a redundant gas
valve to assure safety shut−off as required by A. .A. or
C. .A. Units may be installed in upflow or horizontal posi
tion.
All specifications in this manual are subject to change. Pro
cedures outlined in this manual are presented as a recom
mendation only and do not supersede or replace local or
state codes. In the absence of local or state codes, the
guidelines and procedures outlined in this manual (except
where noted) are recommended only and do not constitute
code.
TABLE OF CONTENTS
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Data 3−4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 5−6. . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components 6−15. . . . . . . . . . . . . . . . . . . . . . . . . . .
II Installation 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks 16−17. . . . . . . . . . .
V Typical Operating Characteristics 18. . . . . . . . . . . . . .
VI Maintenance 19−20. . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 21−28. . . . . . . . .
VIII SureLight Troubleshooting uide 29−34. . . . . . . . . .

Page 2
SPECIFICATIONS
Model No. 80UHG2(X)Ć45 80UHG2(X)Ć 0 80UHG3(X)Ć 0 80UHG2(X)Ć75 80UHG3(X)Ć75 80UHG4(X)Ć75
Input Btuh (kW) 45,000 (13.2) 60,000 (17.6) 75,000 (22.0)
Output Btuh (kW) 36,900 (10.8) 49,200 (14.4) 61,700 (18.1) 61,700 (18.1)
A.F.U.E. 80.1% 80.5% 80.1% 80.0%
California Seasonal Efficiency 75.4% 76.4% 75.9% 76.8% 76.8% 76.3%
Flue size connection diameter Ċ in. (mm) round 3 (76) 4 (102)
Temperature rise range Ċ _F (_C) 30 Ć 60 (17 Ć 33) 45 Ć 75 (25 Ć 42)
High static cert. by A.G.A./C.G.A. Ċ in wg. (Pa) .50 (125)
Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)
Blower wheel nominal in. 9 x 7 10 x 7 9 x 7 10 x 7 12 x 8
Blower
wheel
nominal
diameter x width mm 229 x 178 254 x 178 229 x 178 254 x 178 305 x 203
Blower motor output Ċ hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224) 1/2 (373)
Nominal cooling
Tons 1, 1Ć1/2 or 2 2, 2Ć1/2 or 3 1, 1Ć1/2 or 2 2, 2Ć1/2 or 3 2, 2Ć1/2, 3,
3Ć1/2 or 4
Nominal
cooling
that can be added kW 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or7.0 7.0, 8.8 or 10.6 7.0, 8.8, 10.6,
12.3 or 14.1
Shipping weight Ċ lbs. (kg) 1 package 130 (59) 135 (61) 140 (64)
Electrical Characteristics 120 olts Ċ 60 hertz Ċ 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra)
LPG/propane kit LBĆ69845L (38K84)
Twinning Kit 15L38 - 11lbs. (5 kg)
Up-Flow/Horizontal Filter and Filter Rack Kits Single (32J02) Ten Pack ( K 4)
Up Flow/Horizontal
Filter
and
Filter
Rack
Kits
No. & sizeĂofĂfiltersĂ- in. (mm)
Single
(32J02)
Te n
Pack
(K 4)
(1) 16 x 20 x 1 (406 x 508 x 25)
Sidewall Power Venting Kit 79J15 Ċ 25 lbs. (11 kg)
Hanging Bracket Kit LBĆ69957 (4 J ) Ċ 15 lbs. (8 kg)
SPECIFICATIONS
Model No. 80UHG3/4(X)Ć100 80UHG4/5(X)Ć100 80UHG3/4(X)Ć120 80UHG4/5(X)Ć120
Input Btuh (kW) 100,000 (29.3) 120,000 (35.2)
Output Btuh (kW) 82,000 (24.0) 98,400 (28.8)
A.F.U.E. 80.1% 80.0% 80.0% 80.1%
California Seasonal Efficiency 76.5% 77.0% Not A ailable 75.5%
Flue size connection diameter Ċ in. (mm) round 4 (102)
Temperature rise range Ċ _F (_C) 45 Ć 75 (25 Ć 42) 35 Ć 65 (19 Ć 36) 45 Ć 75 (25 Ć 42)
High static certified by A.G.A./C.G.A. Ċ in wg. (Pa) .50 (125) .65 (162) .50 (125)
Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)
Blower wheel nominal in. 12 x 8 12 x 9 12 x 8 12 x 9
Blower
wheel
nominal
diameter x width mm 305 x 203 305 x 229 305 x 203 305 x 229
Blower motor output Ċ hp (W) 1/2 (373) 3/4 (560) 1/2 (373) 3/4 (560)
Nominal cooling Tons 2, 2Ć1/2, 3, 3Ć1/2 or 4 3Ć1/2, 4, 5 or 6 2, 2Ć1/2, 3, 3Ć1/2 or 4 3Ć1/2, 4, 5 or 6
Nominal
cooling
that can be added kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6or21.1
Shipping weight Ċ lbs. (kg) 1 package 175 (79)
Electrical Characteristics 120 olts Ċ 60 hertz Ċ 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra)
LPG/propane kit LBĆ69845K (81J14)
Twinning Kit 15L38 (5 kg)
Up-Flow/Horizontal Filter and Filter Rack Kits Single (4 J14) Ten Pack ( K 5)
Up Flow/Horizontal
Filter
and
Filter
Rack
Kits
No. & sizeĂofĂfiltersĂ- in. (mm)
Single
(4 J14)
Te n
Pack
( K 5)
(1) 20 x 20 x 1 (508 x 508 x 25)
Sidewall Power Venting Kit 79J15 Ċ 25 lbs. (11 kg)
Hanging Bracket Kit LBĆ69957 (4 J ) Ċ 15 lbs. (8 kg)
Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for nonĆweatherized furnaces.
Polyurethane frame type filter is furnished with kit.

Page 3
BLOWER DATA
80UHG2-45, 80UHG2- 0 AND 80UHG2-75 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High MediumĆHigh MediumĆLow Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1270 600 980 460 770 365 570 270
.05 12 1245 590 975 460 770 365 565 265
.10 25 1220 575 975 460 770 365 565 265
.15 37 1195 565 965 455 765 360 560 265
.20 50 1170 550 960 455 760 360 560 265
.25 62 1140 540 950 450 760 360 555 260
.30 75 1110 525 940 445 760 360 550 260
.40 100 1060 500 910 430 750 355 545 255
.50 125 990 465 880 415 740 350 540 255
.60 150 900 425 810 380 690 325 530 250
.70 175 800 380 740 350 630 295 520 245
NOTE Ċ All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
80UHG3- 0 AND 80UHG3-75 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High MediumĆHigh MediumĆLow Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1425 670 1240 585 1000 470 800 380
.05 12 1415 670 1230 580 995 470 800 380
.10 25 1400 660 1220 575 990 465 795 375
.15 37 1385 655 1200 565 985 465 795 375
.20 50 1370 645 1180 555 980 460 790 375
.25 62 1350 635 1160 545 970 460 780 370
.30 75 1330 630 1140 540 955 450 770 365
.40 100 1280 605 1095 515 925 435 750 355
.50 125 1210 570 1040 490 900 425 720 340
.60 150 1135 535 985 465 860 405 680 320
.70 175 1070 505 920 435 800 380 630 300
NOTE Ċ All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
80UHG4-75, 80UHG3/4-100 AND 80UHG3/4-120 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High MediumĆHigh Medium MediumĆLow Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1830 865 1600 755 1325 625 1070 505 880 415
.05 12 1815 855 1585 750 1320 625 1070 505 880 415
.10 25 1800 850 1570 740 1315 620 1070 505 880 415
.15 37 1875 885 1550 730 1310 620 1065 505 875 415
.20 50 1750 825 1530 720 1300 615 1060 500 875 415
.25 62 1725 815 1515 715 1290 610 1050 495 870 410
.30 75 1700 800 1500 710 1275 600 1040 490 870 410
.40 100 1650 780 1460 690 1245 590 1020 480 860 405
.50 125 1600 755 1420 670 1210 570 1000 470 840 395
.60 150 1550 730 1380 650 1170 550 980 460 820 385
.70 175 1480 700 1330 630 1130 535 960 455 790 375
NOTE Ċ All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

Page 4
BLOWER DATA
80UHG4/5Ć100 AND 80UHG4/5Ć120 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High MediumĆHigh Medium MediumĆLow Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s
0 0 2450 1155 2160 1020 1970 930 1700 800 1500 710
.05 12 2440 1150 2155 1015 1965 925 1695 800 1500 710
.10 25 2430 1145 2150 1015 1960 925 1690 800 1495 705
.15 37 2415 1140 2135 1010 1950 920 1685 795 1495 705
.20 50 2400 1135 2120 1000 1940 915 1680 795 1490 705
.25 62 2380 1125 2105 995 1930 910 1675 790 1480 700
.30 75 2360 1115 2090 985 1915 905 1670 790 1470 695
.40 100 2310 1090 2050 965 1870 880 1650 780 1440 680
.50 125 2260 1065 2000 945 1810 855 1610 760 1410 665
.60 150 2180 1030 1950 920 1750 825 1560 735 1370 645
.70 175 2100 990 1890 890 1700 800 1520 715 1330 630
NOTE Ċ All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
FILTER AIR RESISTANCE
cfm (L/s) in. w.g. (Pa)
0 (0) 0.00 (0)
200 (95) 0.01 (2)
400 (185) 0.03 (7)
600 (280) 0.04 (10)
800 (375) 0.06 (15)
1000 (470) 0.09 (22)
1200 (560) 0.12 (30)
1400 (655) 0.15 (37)
1600 (750) 0.19 (47)
1800 (845) 0.23 (57)
2000 (935) 0.27 (67)
2200 (1030) 0.33 (82)
2400 (1125) 0.38 (95)
2600 (1220) 0.44 (110)
HIGH ALTITUDE DERATE
Refer to table below for manifold pressure settings for
Installations at different altitudes and different fuels.
NOTE-In Canada, certification for installations over
4500 ft. (1372 ) above sea level is the jurisdictionof
the local authorities.
Manifold Absolute Pressure in. w.c. (kPa)
ALTITUDE ft. (m)
FUEL 0-4500
(0-1372)
4500-5500
(1372-1676)
5500-6500
(1676-1981)
6500-7500
(1982-2286)
NAT 3.5 (0.87) 3.4 (0.85) 3.3 (0.82) 3.2 (0.80)
LP 9.5 (2.36) 9.2 (2.29) 8.9 (2.21) 8.6 (2.14)
The combustion air inducer pro e switches are factory
set and are not to be adjusted.
At ele ations of 4500 ft. (1372m) or greater, change factory
installed pressure switch to switch listed in table below.
UNIT MODEL PRESSURE SWITCH
PART NUMBER
80UHG-45 NO CHANGE
80UHG-60 NO CHANGE
80UHG-75 88J8001
80UHG-100 18L2401
80UHG-120 18L2401

Page 5
FIGURE 1
VENT ADAPTER CABINET TOP
80UHG
CABINET
CABINET
BOTTOM
HEAT EXCHANGER
ASSEMBLY
BURNER
ASSEMBLY
BLOWER ASSEMBLY
COMBUSTION AIR
INDUCER
FLUE BOX
SECONDARY
LIMITS
FRONT ACCESS
PANEL
DOOR INTERLOCK SWITCH
CONTROL
BOARD
TRANSFORMER
PROVE
SWITCH
80UHG PARTS IDENTIFICATION
FIGURE 2
HEAT EXCHAN ER
COMBUSTION AIR INDUCER
MANIFOLD
ROLLOUT SWITCH (2)
COMBUSTION AIR
PROVE SWITCH
AS VALVE
BURNERS
COLLECTOR
PRIMARY LIMIT
Front
Right
Top
Bottom
Left
Back
HEATING COMPONENTS (shown in horizontal position)

Page 6
FIGURE 3
80UHG BURNER ASSEMBLY (shown in upflow position)
-2 MODEL SHOWN
Top
FLAME
SENSOR
MANIFOLD
ORIFICE
AS VALVE
HEAT EXCHAN ER
VEST PANEL
BURNER
UPPER
BURNER
MOUNTIN
RAIL
LOWER
BURNER
MOUNTIN
RAIL
BURNER BOX
BURNER BOX
TOP
Front
Right
Bottom
Left
Back
PRIMARY LIMIT
ROLLOUT
SWITCHES
SURELI HT
I NITOR
I-UNIT COMPONENTS (Figures 1, 2, 3)
80UHG unit components are shown in figure 1. The gas
al e, combustion air inducer and burners can be acĆ
cessed by remo ing the burner access panel. Electrical
components are mounted to the blower housing.
80UHG units are factory equipped with bottom return air panĆ
els in place. The panels are designed to be field remo ed as
required for bottom air return. Knockout panels are pro ided
for side return air.
CAUTION
Ele trostati dis harge an affe t ele troni
omponents. Take pre autions during furna e
installation and servi e to prote t the furna e's
ele troni ontrols. Pre autions will help to
avoid ontrol exposure to ele trostati disĆ
harge by putting the furna e, the ontrol and
the te hni ian at the same ele trostati potenĆ
tial. Neutralize ele trostati harge by tou hing
hand and all tools on an unpainted unit surfa e,
su h as the gas valve or blower de k, before perĆ
forming any servi e pro edure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
1- Control Transformer (T1)
A transformer located on the blower housing pro ides
power to the low oltage section of the unit. Transformers
on all models are rated 30VA with a 120V primary and a
24V secondary.
2-Door Interlock Switch (S51)
A door interlock switch rated 16A at 125VAC is wired in seĆ
ries with line oltage. When the blower door is remo ed the
unit will shut down.
DANGER
Shock hazard.
Spark related components contain high voltage.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, simĆ
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.

Page 7
3− Furnace Control (A3)
80UHG−2, −3 Models
80UH −2 and −3 model units are equipped with the Len
nox SureLight ignition system. The system consists of
ignition control board (figure 6 with control terminal desig
nations in table 4) and ignitor (figure 7). The board and ig
nitor work in combination to ensure furnace ignition and
ignitor durability. The SureLight integrated board controls
all major furnace operations. The board also features two
LED lights for troubleshooting and two accessory termi
nals rated at (4) four amps. See table 3 for troubleshoot
ing diagnostic codes. Table 1 and 2 show jack plug termi
nal designations. Units equipped with the SureLight
board can be used with either electronic or electro−me
chanical thermostats without modification. The Sur
eLight ignitor is made of durable silicon−nitride. Ignitor
longevity is also enhanced by voltage ramping by the
control board. The board finds the lowest ignitor tempera
ture which will successfully light the burner, thus increas
ing the life of the ignitor. Each time power is applied to the
furnace, the SureLight board performs a selfcheck in
cluding energizing the combustion air blower for a period
of 1 second.
TABLE 1
SureLight BOARD J15 (J2) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1 Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 2
SureLight BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1 Primary Limit / Pressure Switch Out
2Secondary Limit
324V
4Not Used
5Rollout Switch In
624V
7Primary Limit In
8round
9as Valve In
10 Pressure Switch In
11 Rollout Switch Out
12 as Valve Out
a−Electronic Ignition (See Figure 5)
On a call for heat the SureLight control monitors the com
bustion air inducer pressure switch. The control will not be
gin the heating cycle if the prove switch is closed (by−
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differ
ential in the prove switch is great enough, the prove switch
closes and a 15−second pre−purge begins. If the prove
switch is not proven within 2−1/2 minutes, the control goes
into Watchguard−Pressure Switch mode for a 5−minute re−
set period.
After the 15−second pre−purge period, the SureLight igni
tor warms up for 20 seconds during which the gas valve
opens at 19 seconds for a 4−second trial for ignition. The
ignitor stays energized for the first second of the 4−second
trial. 80UH units equipped with control 10M9301: ignitor
remains energized during the 4 second trial until flame is
sensed. If ignition is not proved during the 4−second peri
od, the control will try four more times with an inter purge
and warm−up time between trials of 35 seconds. After a to
tal of five trials for ignition (including the initial trial), the
control goes into Watchguard−Flame Failure mode. After a
60−minute reset period, the control will begin the ignition
sequence again.
The SureLight control board has an added feature that
prolongs the life of the ignitor. After a successful ignition,
the SureLight control utilizes less power to energize the ig
nitor on successive calls for heat. The control continues to
ramp down the voltage to the ignitor until it finds the lowest
amount of power that will provide a successful ignition.
This amount of power is used for 255 cycles. On the 256th
call for heat, the control will again ramp down until the low
est power is determined and the cycle begins again.
b−Fan Time Control
The fan on time of 45 seconds is not adjustable. Fan off
time (time that the blower operates after the heat demand
has been satisfied) can be adjusted by flipping the dip
switches located on the SureLight integrated control. The
unit is shipped with a factory fan off setting of 90 seconds.
Fan off time will affect comfort and is adjustable to satisfy
individual applications. See figure 4.
FIGURE 4
FANOFF TIME ADJUSTMENT
To adjust fan−off timing, flip dip switch to desired setting.
60sec. 90sec. 120sec. 180sec.

Page 8
The SureLight board is equipped with two LED lights for troubleshooting. The diagnostic codes are listed below in table 3.
TABLE 3
DIAGNOSTIC CODES
MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.
LED #1 LED #2 DESCRIPTION
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power − Normal operation
Also signaled during cooling and continues fan.
SIMULTANEOUS FAST
FLASH
SIMULTANEOUS FAST
FLASH Normal operation − signaled when heating demand initiated at thermostat.
SLOW FLASH ON
Primary or Secondary limit open. Units with board 12L69: Limit must close within
5 trials for ignition or board goes into one hour limit Watchguard. Units with board
56L84: Limit must close within 3 minutes or board goes into one hour limit Watch
guard.
OFF SLOW FLASH
Pressure switch open or has opened 5 times during a single call for heat; OR:
Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch
closed prior to activation of combustion air blower.
ALTERNATIN SLOW
FLASH
ALTERNATIN SLOW
FLASH Watchguard − burners fail to ignite.
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: 9 pin connector improperly attached.
ON
ON
OFF
ON
OFF
ON
Circuit board failure or control wired incorrectly.
FAST FLASH SLOW FLASH Main power polarity reversed. Switch line and neutral.
SLOW FLASH FAST FLASH Low flame signal. Measures below 0.2 microAmps. Replace flame sense rod.
ALTERNATIN FAST
FLASH
ALTERNATIN FAST
FLASH
Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR:
Open ignitor circuit.
NOTE − Slow flash equals 1 Hz (one flash per second). Fast flash equals 3 Hz (three flashes per second). Drop out fla e sense current < 0.15 icroA ps
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
DEMAND
CA
B
GAS VALVE
15
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
38
ÉÉÉÉÉÉÉÉ
IGNITOR
341
Pre −Purge Ignitor Warmup Trial for
Ignition
Post
Purge
5 SEC80
*Blower on time will be 45 seconds after ignition. Blower off time will depend on OFF TIME" Setting.
INDOOR BLOWER
ÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉ
FIGURE 5
Blower On"
Delay
SureLight Control Ignition Sequence
(Control 5 L8401 ONLY)
35

Page 9
SURELIGHT INTEGRATED CONTROL BOARD
FIGURE 6
XFMR-N
Flame
sense
4-Flame Sensor 80UHG -2 models
A flame sensor is located on the left side of the burner
support. See figure 8. The sensor is mounted on a
bracket in the burner support and the tip protrudes
into the flame envelope of the left-most burner. The
sensor is fastened to burner supports and can be reĆ
moved for service without removing any part of the
burners. During operation, flame is sensed by current
passed through the flame and sensing electrode. The
SureLight control allows the gas valve to remain open
as long as flame signal is sensed.
NOTE - The 80UHG furnace contains electronic
components that are polarity sensitive. Make sure that
the furnace is ired correctly and is properly
grounded.
PARK
TERMINAL DESIGNATIONS
COOL-H
HEAT-H
EAC-H
HUM-H
XFMR-H
LINE-H
LINE-N
HUM-N
EAC-N
XFMR-N
CIR-N
Blower - Cooling Speed (120VAC)
Blower - Heating Speed (120VAC)
Electronic Air Cleaner (120VAC)
Humidifier (120VAC)
Transformer (120VAC)
Input (120VAC)
Input (Neutral)
Humidifier (Neutral)
Electronic Air Cleaner (Neutral)
Transformer (Neutral)
Not Used
(FLAME SENSE)
TABLE 4
FIGURE 7
SURELIGHT IGNITOR
SureLight Ignitor
FIGURE 8
NORMAL FLAME SIGNAL u 0.2 MICROAMPS
LOW FLAME SIGNAL v 0.2 MICROAMPS
MINIMUM FLAME SIGNAL v 0.15 MICROAMPS
BURNER
FLAME
SENSOR
SIDE VIEW END VIEW
1/4 in. 7 mm
 1/32 in. 0.79
mm
3/16 in.
4.7 mm
11/16 in. 18 mm
 1/32 in. 0.79
mm

Page 10
5- Furnace Control (A3) 80UHG-1 Model
80UHG units are equipped with an integrated ignition/blower
control (EGCĆ2) which controls ignition, safety circuits,
blower operation, fan off timing, and allows for thermostat
connection and troubleshooting. The EGCĆ2 is a printed
circuit board which is di ided into two sections, 120 and
24VAC. Line oltage comes into the board on the 120VAC
side. See figure 10. Terminal designations are listed in
tables 6 and 7.
Ignition Control
80UHG units use the EGC-2 direct spark integrated
ignition control. The EGC-2 controls and monitors the
entire sequence of operation. On a call fo r he at fr o m th e
thermostat the control monitors the combustion air inĆ
ducer pro e switch. The control will not begin the heatĆ
ing cycle if the pro e switch is closed (byĆpassed). Once
the pro e switch is determined to be open, the combustion
air inducer is energized. When the differential in pressure
across the pro e switch is great enough, the pro e switch
closes and a 15 second preĆpurge period begins. If the
pro e switch does not close within 2 1/2 minutes, the conĆ
trol goes into 5 minute watchguard. After the preĆpurge peĆ
riod, the gas al e will open and ignition (spark) will be atĆ
tempted for 10 seconds. After ignition, the co nt r ol ini tiate s a
ten second flame stabilization period. The flame stabiĆ
lization period allows the burners to heat up and the
flame to stabilize. Once flame is established, the control will
constantly monitor the burner flame using flame rectification.
Flame failure response time is 0.8 seconds.
If the initial attempt for ignition fails, the sequence is reĆ
peated up to fi e times. After the fifth trial, the control goes into
Watchguard"*. During watchguard mode, the entire unit will
be deĆenergized for one hour. After one hour the control will
repeat the ignition sequence. Watchguard may be manually
reset by breaking and remaking thermostat demand.
*NOTE-If fla e is established beyond the 10 second fla e
stabilization period then lost, the control resets for five ore
ignition trials. The control can be reset five ti es during one
unsa tis f ied ther os tat de and, pr ovi ding a ax i u
of 25 trials for ignition.
Safety Circuits
During the entire heating demand the control monitors the
safety circuits. If the primary or secondary heating limits
open, the control deĆenergizes the main gas al e and
combustion air blower while the indoor blower remains enĆ
ergized. When the limit automatically resets, the ignition seĆ
quence also resets. If either of the limits trip fi e consecuĆ
ti e times during one unsatisfied thermostat demand, the
control will go into watchguard for one hour.
The control monitors main al e oltage. If oltage is sensed
when no oltage should be present, the control deĆenergizes
the combustion air inducer which terminates oltage to the
al e. The system goes into hard lockĆout which is reset only
by remo ing power to the unit.
If flame is sensed when no flame should be present, the conĆ
trol will energize the combustion and indoor blowers. The
unit will remain locked in this sequence until the flame is no
longer sensed or the main power is turned off to reset the
control.
The rollĆout circuit is also monitored by the EGCĆ2 control. If
the switch opens, the control will deĆenergize the gas
al e, combustion air inducer, and indoor blower. The
unit will remain deĆenergized until the switch is manualĆ
ly reset.
DANGER
Shock hazard. Avoid personal injury. Make sure to
disconnect power before changing fan off" timing.
Blower Operation / Fan Off Timings
Fan off" timing (time that the blower operates after the heat
demand has been satisfied) can be adjusted by mo ing the
jumper on the EGCĆ2 blower control board. Figure 9 shows
the arious fan off" timings and how jumper should be posiĆ
tioned. To adjust fan off " timing, gently disconnect jumper
and reposition across pins corresponding with new timing.
Unit is shipped with a factory fan off" setting of 180 seconds.
Fan on" time is factory set at 45 seconds following the
opening of the main gas al e and is not adjustable.
Fan off" time will affect comfort and efficiency and is adĆ
justable to satisfy indi idual applications. The fan off" timĆ
ing is initiated after a heating demand but not after a coolĆ
ing demand.
NOTEĊIf fan off" ti e is set too low, residual heat in
heat exchanger ay cause pri ary li it S10 to trip, reĆ
sulting in frequent cycling of blower. If this occurs, adjust
blower to longer fan off" ti e setting.
FIGURE 9
FANĆOFF TIME ADJUSTMENT
180 60
120 90
To adjust fanĆoff timing:
Remo e jumper from EGCĆ2 and select
one of the other pin combinations to
achie e the desired time.
TIMING
JUMPER
TIMING PINS
(seconds)
Lea e jumper off for
240 second fanĆoff timing.

Page 11
Thermostat Connection
Thermostat wires are connected to the terminal strip
found on the EGCĆ2 control board.
Troubleshooting
The EGCĆ2 control board is equipped with two diagnostic
green LEDs to indicate the mode of failure. The LED lights
are marked DIAG #1 and DIAG #2. The codes are gi en in
table 5.
A slotted edge connector is also pro ided for the Lennox
Diagnostic Module (part number 11K75). See figure 10.
When connected to the EGCĆ2 control board, the module disĆ
plays (in words) the diagnostic condition.
TABLE 5
EGCĆ2 DIAGNOSTIC CODES
DIAG #2 DIAG #1 DIagnosti Condition
Simultaneous
Flash Simultaneous Flash
Power ON". Normal Operation. InĆ
creased flash rate indicates there
is a heating demand.
On Flash Primary or Secondary Limit Switch Open.
AutoĆReset Switch.
Flash Off Pressure Switch Watchguard, pressure switch opened during
operation.
Alternate
Flash Alternate Flash Watchguard, burners failed to ignite.
Off Flash Flame sensed without
al e energized.
Flash On RollĆout Switch Open.
ManualĆReset Switch.
Continuous
On Continuous On Circuit board selfĆcheck failure or
ignition/blower control
is wired incorrectly.
EDGE
CONNECTION
FIGURE 10
80UHG-1 MODEL INTEGRATED CONTROL (EGC-2)
(Shown as installed in horizontal left hand application)
(See tables and 3 for terminal designations)
THERMOSTAT
TERMINAL STRIP
(DETACHABLE)
BLOWER TIME
ADJUSTMENT
JUMPER
DIAGNOSTIC MODULE
DIAGNOSTIC LEDS
DIAGNOSTIC CODE ERASE JUMPER
(Remo e power to control and short pins for
10 seconds to erase pre ious code.)
24VAC
PLUG P20
5
6
7
8 9 10 11 12 13 15
123
4
14
1
2
3
4
6
5
7
8
9

Page 12
TABLE
BLOWER CONTROL A15 TERMINAL DESIGNATIONS
Termi nal
Designation
(See fig. 10)
Type Fun tion
RScrew Strip 24VAC to Thermostat (Red)
GScrew Strip Manual Fan Input from Thermostat
(Green)
WScrew Strip Heat Demand Input from Thermostat
(White)
YScrew Strip Cool Demand Input from Thermostat
(Yellow)
CScrew Strip Common Ground to Thermostat
11/4" Spade 24VAC Hot from Transformer
21/4" Spade 24VAC Return to Transformer
31/4" Spade 24VAC Ground
4, 5, 6 1/4" Spade 120VAC Return - 120VAC Common
71/4" Spade 120VAC Return - 120VAC Common
Input
81/4" Spade Combustion Blower (Line Voltage)
91/4" Spade Heat Only Accessory (Line Voltage)
10 1/4" Spade 120VAC Hot to Transformer
11 1/4" Spade 120VAC Hot Input
12, 13 1/4" Spade Accessories (Line Voltage)
14 1/4" Spade ACB Cool Speed (Line Voltage)
15 1/4" Spade ACB Heat Speed (Line Voltage)
TABLE 7
EGCĆ2 CONTROL JACK/PLUG 20 TERMINAL DESIGNATIONS
Pin # Fun tion
1Rollout Switch Out
2 Spare
3Gas Val e Common
4Pressure Switch Return
5Hi Limit Return / Pressure Switch Out
6Flame Sensor
7Gas Val e Out
8High Limit Out
9Rollout Switch Return
-Blower Motors and Capacitors
All 80UHG units use direct dri e blower motors. All motors
used are 120V permanent split capacitor motors to ensure
maximum efficiency. See table 8 for ratings.
TABLE 8
80UHG BLOWER RATINGS 120V 1PH
BLOWER MOTOR HP
80UHG2
80UH 3
80UH 3/4
CAP
1/2
1/3
1/4 5MFD 370V
5MFD 370V
7.5MFD 370V
80UH 5/6
80UH 4
80UH 4/5
1/2 7.5MFD 370V
3/4 40MFD 370V
3/4 40MFD 370V
FIGURE 11
SUPPLY AIR BLOWER
AND SECONDARY LIMITS
Front
Bottom
Right
Left
Top Back
BLOWER
MOTOR
To Remo e Blower From Unit: Remo e Bolts and
Wiring Jackplugs. Then Slide Out Front of Unit.
MOTOR
CAPACITOR
SECONDARY
LIMITS (S21)
7-Combustion Air Inducer (B )
All 80UHG units use a combustion air inducer to mo e air
through the burners and heat exchanger during heating
operation. The blower uses a 120VAC motor. The motor
operates during all heating operation and is controlled by
furnace control A3. The blower also operates for 15 seĆ
conds before burner ignition (preĆpurge) and for 5 seconds
after the gas al e closes (postĆpurge)
A pro ing switch connected to the combustion air inducer
housing is used to pro e combustion air inducer operation.
The switch monitors air pressure in the blower housing. DurĆ
ing normal operation, the pressure in the housing is negaĆ
ti e. If pressure becomes less negati e (signifying an obĆ
struction) the pro e switch opens. When the pro e switch
opens, the furnace control (A3) immediately closes the gas
al e to pre ent burner operation.
8-Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box. Each furnace is equipped with two
identical switches. One switch is located o er the leftmost
burner and the other switch is located o er the rightmost
burner. The limit is a N.C. SPST manualĆreset limit conĆ
nected in series with the ignition control A3. When S47

Page 13
senses rollout, the ignition control immediately stops igniĆ
tion and closes the gas al e. If unit is running and flame
rollout is detected, the gas al e will close and ignition conĆ
trol will be disabled. Rollout can be caused by a blocked
flue or lack of combustion air. The switch is factory set and
cannot be adjusted. The setpoint will be printed on the side of
the limit. The switch can be manually reset. To manually reĆ
set a tripped switch, push the reset button located on the
control.
FIGURE 12
ROLLOUT SWITCH (S47)
MANUAL
RESET BUTTON
9-Primary Limit Control (S10)
FIGURE 13
80UHG SERIES UNITS
LIMIT CONTROL FOR
THIS TYPE AUTOĆRESET LIMIT
IS USED FOR THE PRIMARY LIMIT (S10) AND
RIGHT SECONDARY LIMIT (S21)
(see FIGURE 11)
The primary limit (S10) on 80UHG units is located in the
middle of the heating estibule panel. When excess heat is
sensed in the heat exchanger, the limit will open. If the limit is
tripped, the furnace control energizes the supply air blower
and closes the gas al e. The limit automatically resets when
unit temperature returns to normal. The switch is factory set
and cannot be adjusted. The switch may ha e a different
setpoint for each unit model number. Howe er, the setpoint
will be printed on the side of the limit.
10-Secondary Limit Controls (S21)
The secondary limit (S21) on 80UHG units is located in the
blower compartment in the back side of the blower housing.
When excess heat is sensed in the blower compartment, the
limit will open. If the limit is tripped, the furnace control enerĆ
gizes the supply air blower and closes the gas al e. The limit
automatically resets when unit temperature returns to normal.
The switch is factory set and cannot be adjusted. The setĆ
point will be printed on the limit.
Two limits are supplied in each furnace. 80UHG3, 80UHG4
and 80UHG4/5 model units built prior to Apri 1999, will
ha e one each of style shown in figures 13 and 14. If stick
limit (figure 14) suffers frm nuisance trips on the abo e
model units and the furnace is in the horizontal position, reĆ
place with limit kit no. 50L98. All 80UHG2 model units will
ha e one of each style shown in figures 13 and 14.
INSULATING COVER (s)
FIGURE 14
SECONDARY LIMIT CONTROL (S21)
FOR 80UHG SERIES UNITS
SPADE CONNECTORS
INSULATING COVER
LIMIT
LIMIT
THIS TYPE AUTOĆRESET LIMIT IS
USED FOR THE LEFT SECONDARY
LIMIT (S21) (see FIGURE 11)
11-Spark Electrode and Flame Sensor
80UHG-1 Models
Figure 17 shows the arrangement of flame sensor, spark
electrode and burners. The ignition control uses direct
spark to ignite the rightmost burner and the burners crossĆ
light to the left. The flame sensor uses flame rectification to
sense combustion. A flame retention ring in the end of
each burner is used to maintain correct flame length and
shape and to keep the flame from lifting off the burner
head.
Figure 18 shows the gap between tip of the electrodes and
the burner surface, and the gap between the sensor and
burner surface.
12-Gas Valve
The 80UHG uses a gas al e manufactured by HoneyĆ
well or White Rodgers. The al e is internally redundant to
assure safety shut-off. If the gas al e must be replaced,
the same type al e must be used.
24VAC terminals and gas control knob are located on top of
the al e. All terminals on the gas al e are connected to
wires from the electronic ignition control. 24V applied to the
terminals energizes the al e.
Inlet and outlet pressure taps are located on the al e. A reguĆ
lator adjustment screw (figures 15 and 16) is located on the
al e.
LPG changeo er kits are a ailable from Lennox. Kit s include
burner orifices and a gas al e regulator con ersion kit.

Page 14
WHITE RODGERS 3 E SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 15
ON
OFF
HONEYWELL VR8205 SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 1
FIGURE 17
TYPICAL BURNER/ELECTRODE ORIENTATION
BURNER
FLAME RETENTION RIN
UPPER BURNER
MOUNTIN RAIL
LOWER BURNER
MOUNTIN RAIL
MANIFOLD ORIFICE
Right Left
Top
Bottom
FLAME SENSOR
SPARK ELECTRODE ROUND
1/8"(+1/64")
23/32 in.
(18 mm)
80UHG-1 MODEL SHOWN
FIGURE 18
SPARK ELECTRODE
SPARK ELECTRODE TO BURNER GAP
80UHG-1 MODEL SHOWN
BURNER
FLAME SENSOR TO BURNER GAP
BURNER
FLAME SENSOR
SPARK
ELECTRODE
5/16 in.
(7 mm)
5/16 in.
(7 mm)
13-Combustion Air Blower Prove
Switch (S18)
80UHG series units are equipped with a combustion air
pro e switch located on the estibule panel. The switch is
connected to the combustion air inducer housing by means
of a flexible silicone hose. It monitors air pressure in the
combustion air blower housing.
The switch is a singleĆpole singleĆthrow pressure switch
electrically connected to the furnace control. The purpose
of the switch is to pre ent burner operation if the combusĆ
tion air blower is not operating or if the flue becomes obĆ
structed.

Page 15
FIGURE 19
PROVE SWITCH
COMBUSTION AIR INDUCER
PROVE SWITCH
Normally Open
Closes on Negati e Pressure
PROVE
SWITCH
Sensing Tube
Attaches to Top
Side Of Blower
Top
Bottom
Left
Right
Back
Front
On startĆup, the switch senses that the combustion air
blower is operating. It closes a circuit to the furnace control
when pressure inside the combustion air blower deĆ
creases to a certain set point. Set points ary depending
on unit size. The pressure sensed by the switch is relati e
to atmospheric pressure. If the flue becomes obstructed
during operation, the switch senses a loss of negati e
pressure (pressure becomes more equal with atmospherĆ
ic pressure) and opens the circuit to the furnace control
and gas al e. A bleed port on the switch allows dry relati Ć
ity air in the estibule to purge switch tubing, to pre ent
condensate build up. The switch also has an internal inline
orifice, designed to pre ent nuisance shut downs due to
erratic ent pressure fluctuations.
The switch is factory set and is not field adjustable. It is a
safety shutĆdown control in the furnace and must not be
by-passed for any reason. If switch is closed or by-passed,
the control will not initiate ignition at start up.
II-PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installation
instructions and applicable codes.
III-STARTĆUP
A-Preliminary and Seasonal Checks
1 - Inspect electrical wiring, both field and factory installed
for loose connections. Tighten as required.
2 - Check oltage at disconnect switch. Voltage must be
within range listed on the nameplate. If not, consult the
power company and ha e oltage condition corrected
before starting unit.
B-Heating StartĆUp
WARNING
Shock and burn hazard.
80UHG-1 units are equipped with a direct spark igniĆ
tion system. Do not attempt to light manually.
1 - STOP! Read the safety information at the beginning
of this section.
2 - Set thermostat to lowest setting.
3 - Turn off all electrical power to appliance.
4 - This appliance is equipped with an ignition de ice
which automatically lights the burners. Do not try to
light the burners by hand.
5 - Remo e top access panel.
6 - White Rodgers 36E Gas Valve -- Switch le er to
OFF. See figure 15.
Honeywell VR8205 Gas Valve -- Turn knob on gas
al e clockwise to OFF. Do not force. See figĆ
ure 16.
7 - Wait fi e (5) minutes to clear out any gas. If you then
smell gas, STOP! Close manual main shut-off al e to
the furnace. Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's instructions.
If you do not smell gas go to next step.
8 - White Rodgers 36E Gas Valve -- Switch gas al e le er
to ON.
Honeywell VR8205 Gas Valve -- Turn knob on gas
al e counterclockwise to ON. Do not force.
9 - Replace access panel.
10- Turn on all electrical power to unit.
11- Set thermostat to desired setting.
NOTE–When unit is initially started, steps 1 through 11
may need to be repeated to purge air from pilot line.
12- If the appliance will not operate, follow the instructions
To Turn Off Gas To Unit".
Turning Off Gas To Unit
1 - Set thermostat to lowest setting.
2 - Turn off all electrical power to unit if ser ice is to be
performed.
3 - Remo e access panel.
4 - Switch le er on White Rodgers gas al e to OFF; turn
knob on Honeywell al e clockwise to OFF. Do not
force.
5 - Replace access panel.
C-Safety or Emergen y Shutdown
Turn off unit power. Close manual and main gas valves.
D-Extended Period Shutdown
Turn off thermostat or set to UNOCCUPIED" mode. Close
all gas al es (both internal and external to unit) to guaranĆ
tee no gas leak into combustion chamber. Turn off power
to unit. All access panels, co ers and ent caps must be in
place and secured.

Page 16
IV-HEATING SYSTEM SERVICE CHECKS
A-A.G.A./C.G.A. Certification
All units are A.G.A. and or C.G.A. design certified without
modifications. Refer to the 80UHG Operation and InstallaĆ
tion Instruction Manual Information.
B-Gas Piping
as supply piping should not allow more than 0.5"W.C.
drop in pressure between gas meter and unit. Supply
gas pipe must not be smaller than unit gas connection.
Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.
C-Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shutĆoff valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas al e must be
disconnected and isolated. Gas al es can be damaged if
subjected to more than 0.5psig (14" W.C.). See figure 20. If
the pressure is equal to or less than 0.5psig (14"W.C.), use
the manual shut-off al e before pressure testing to isoĆ
late furnace from gas supply.
FIGURE 20
MANUAL MAIN SHUT-OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSI (14"W.C.)
AS VALVE
CAP
GAS PIPING TEST PROCEDURE
FIELD PROVIDED
LINE PRESSURE TAP
When checking piping connections for gas leaks, use preĆ
ferred means. Kitchen detergents can cause harmful corroĆ
sion on arious metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is a ailable
through Lennox under part number 31B2001. See Corp.
8411-L10, for further details.
Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.
D-Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap (field pro ided). See figure 20. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas al e or
o erfire. For 80UHG-45,60 and 75 BTUH natural gas
units, operating pressure at the unit must be a minimum
4.5"W.C. For the 80UHG-100 and 120 BTUH units, the opĆ
erating pressure must be a minimum of 5.0"W.C. For L.P.
gas units, operating pressure at unit gas connection must
be a minimum of 11.0" W.C.
On multiple unit installations, each unit should be checked
separately, with and without other units operating. Supply
pressure must fall within range listed in pre ious paraĆ
graph.
E-Check Manifold Pressure
After line pressure has been checked and adjusted, check
manifold pressure. Mo e pressure gauge to outlet presĆ
sure tap located on unit gas al e (GV1). Checks of manĆ
ifold pressure are made as erification of proper regulator
adjustment. Manifold pressure for the 80UHG can be meaĆ
sured at any time the gas al e is open and is supplying gas
to the unit. Normal manifold pressure for natural gas units is
3.5 in. W.C. For LP/propane gas the correct manifold presĆ
sure is 9.5 in. W.C.
IMPORTANT
For safety, connect a shutĆoff valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
Operating Pressure (outlet) in. W.C.
TABLE 9
GAS VALVE REGULATION
3.5 +0 -0.3Natural
L.P. 9.5 + 0.5
Unit (Fuel)
The gas valve is factory set and should not require adĆ
justment. All gas valves are factory regulated. See
table 9. See specifications section of this manual for
High Altitude manifold pressure settings.

FIGURE 21
TRANSDUCER
(PART #78H5401)
Page 17
Manifold Adjustment Procedure:
1 - Connect a test gauge to outlet pressure tap on gas
al e. Start unit and allow 5 minutes for unit to reach
steady state.
2 - While waiting for the unit to stabilize, notice the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue. L.P. gas should burn
mostly blue with some orange streaks.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to alues gi en in
table 9.
NOTE-Shut unit off and re ove ano eter as soon as
an accurate reading has been obtained. Take care to
replace pressure tap plug.
F- Proper Gas Flow (Approximate)
Furnace should operate at least 5 minutes before
checking gas flow. Determine time in seconds for two
revolutions of gas through the meter. (Two revoluĆ
tions assures a more accurate time.) Divide by two
and compare to time in table 10 below. Adjust manĆ
ifold pressure on gas valve to match time needed.
NOTE- To obtain accurate reading, shut off all other
gas appliances connected to eter.
TABLE 10
GAS METER CLOCKING CHART
Seconds for One Revolution
80UHG
Uit
Natural LP
Unit 1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
-45 80 160 200 400
-60 60 120 150 300
-100 36 72 90 180
-120 30 60 75 150
Natural-1000 btu/cu ft LP-2500 btu/cu ft
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
G-Flame Signal
A microamp DC meter is needed to check the flame signal
on the ignition control.
Flame (microamp) signal is an electrical current which passes
from the furnace control through the sensor during unit operaĆ
tion. Current passes from the sensor through the flame to
ground to complete a safety circuit.
To Measure Flame Signal - Ignition Control:
A transducer (Part
#78H5401 a ailable from
Lennox Repair Parts) is
required to measure
flame signal if meter used
will not read a low micro
amp signal. ĂSeeĂfigĆ
ureĂ21. The transducer
con erts microamps to olts on a 1:1 con ersion. Flame sigĆ
nal should for the EGC control should be 1.0 - 5.0 with a lock-
out signal of .45 nominal microamps, therefore a reading of
1.0 - 5.0 nominal olts should be read on the meter. Flame
signal for the SureLight control should read 0.7 microamps
with a lockout signal of .15 microamps. A digital readout meter
must be used. The transducer plugs into most meters.
See figure 22 for proper use of transducer.
1 - Set the olt meter to the DC oltage scale. Insert
transducer into the VDC and common inputs. ObĆ
ser e correct polarities. Failure to do so results in
negati e (-) alues.
2 - Turn off supply oltage to control.
3 - Disconnect ignition control flame sensor wire from the
flame sensor.
4 - Connect (-) lead of the transducer to flame sensor.
5 - Connect (+) lead of transducer to the ignition control senĆ
sor wire.
6 - Turn supply oltage on and close thermostat contacts to
cycle system.
7 - When main burners are in operation for two minutes, take
reading. Remember 1 DC olt = 1 DC microamp.
SET DIAL TO MEASURE VDC
(+)
(-)
(-) TO
FLAME SENSOR
NOTE-MUST USE DIGITAL METER
RED COLLAR
INDICATES
POSITIVE
LEAD
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 22

FIGURE 23
STATIC PRESSURE
TEST
MANOMETER
80UHG UNIT
Page 18
WARNING
Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property
damage, personal injury or loss of life.
V-TYPICAL OPERATING CHARACTERISTICS
A-Blower Operation and Adjustment
NOTE- The following is a generalized procedure and
does not apply to all ther ostat controls.
1 - Blower operation is dependent on thermostat control
system.
2 - Generally, blower operation is set at thermostat subĆ
base fan switch. With fan switch in ON position, blower
operates continuously on heating speed. With fan
switch in AUTO position, blower cycles with demand or
runs continuously while heating or cooling circuit cycles.
3 - Depending on the type of indoor thermostat, blower
and entire unit will be off when the system switch is in
OFF position.
B-Temperature Rise
Temperature rise for 80UHG units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of AIR TEMP. RISE
°F" listed on the unit rating plate.
To Measure Temperature Rise:
1 - Place plenum thermometers in the supply and return
air plenums. Locate supply air thermometer in the first
horizontal run of the plenum where it will not pick up raĆ
diant heat from the heat exchanger.
2 - Set thermostat to highest setting.
3 - After plenum thermometers ha e reached their highĆ
est and steadiest readings, subtract the two readings.
The difference should be in the range listed on the unit
rating plate. If the temperature is too low, decrease
blower speed. If temperature is too high, first check
the firing rate. Pro ided the firing rate is acceptable, inĆ
crease blower speed to reduce temperature. To
change blower speed taps see the Blower Speed Taps
section in this manual.
C-External Static Pressure
1 - Tap locations shown in figure 23.
2 - Punch a 1/4" diameter hole
in supply and return air pleĆ
nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with perĆ
magum. Connect the zero
end of the manometer to the
discharge (supply) side of the system. On ducted sysĆ
tems, connect the other end of manometer to the reĆ
turn duct as abo e. For systems with non-ducted reĆ
turns, lea e the other end of the manometer open to
the atmosphere.
3 - With only the blower motor running and the e aporator
coil dry, obser e the manometer reading. Adjust blowĆ
er motor speed to deli er the air desired according to
the job requirements.
4 - External static pressure drop must not be more than
0.5" W.C.
5 - Seal around the hole when the check is complete.
D-Blower Speed Taps Leadless Motors
80UHG-1 Models
Blower speed tap selection is accomplished by changing the
taps at the blower motor harness connector. Disconnect harĆ
ness connector from motor to expose speed selectors.
Blower speed selections are listed in table 11.
To Change Blower Speed:
1 - Turn off electric power to furnace.
2 - Remo e blower access door.
Disconnect blower motor harness from motor.
3 - Select desired speeds for heating and cooling. (Red =
heating, Black = cooling, White = common).
4 - Depress harness connector tab to release wire termiĆ
nal. Select connector location for new speed (refer to
unit wiring diagram). Insert wire terminal until it is seĆ
curely in place. See figure 24.
5 - Replace harness connector to motor.
TABLE 11

Page 19
FIGURE 24
BLOWER SPEED TAP SELECTION
Leaded Motors HARNESS
CONNECTOR
MOTOR
DEPRESS TAB TO RELEASE
WIRE TERMINAL. SELECT
CONNECTOR LOCATION
FOR NEW SPEED (REFER TO
UNIT WIRING DIAGRAM). INĆ
SERT WIRE UNTIL IT IS SEĆ
CURELY IN PLACE.
E-Blower Speed Taps Leaded Motors
80UHG-2 Models
Blower speed tap changes are made on the SureLight
control board. See figure 6. Unused taps must be secured
on two dummy terminals labeled "PARK on the SureLight
board. The heating tap is connected to the "HEAT-H " terĆ
minal and the cooling tap is connected to the "COOL-H"
terminal. The continuous blower tap is the same as the
heating tap.
To change existing heat tap, turn off power then switch out
speed tap on "HEAT-H" with tap connected to "PARK" .
See table 12 for blower motor tap colors for each speed.
TABLE 12
VI-MAINTENANCE
At the beginning of each heating season, the system
should be checked as follows:
A-Filters
Return air filter is not supplied with unit. See Optional AcĆ
cessaries section in this manual for filter and rack size. A
filter must be used in order to ensure long life and proper
operation. The filter is located in the return air duct or return
air register. Filters must be cleaned or replaced when dirty
to assure proper unit operation.
B- Heat Exchanger and Burners
Due to dimples designed in the heat exchanger, cleanĆ
ing is not recommended. Removal is for inspection
only.
NOTE-Use papers or protective covering in front of furĆ
nace while cleaning furnace.
To clean burners:
1 - Remo e screws holding upper burner mounting rail (figĆ
ure 17). Remo e rail.
2 - Slide burners off each orifice pull burners from heat exĆ
changer.
3 - Clean holes in burner head (retention ring) with a wire
brush. See figure 17.
4 - With a shop acuum or rags, clean out soot and scale
deposits from burners.
5 - Remo e screws securing flue box to estibule panel.
Remo e flue box from unit. Lea e combustion air
blower attached to flue box.
6 - With a shop acuum or rags, clean out soot and scale
deposits from heat exchanger tubes and flue box. If turĆ
bulators are remo ed (figure 1) make sure they are reĆ
installed before reassembling units.
7 - Inspect heat exchanger for corrosion damage, holes or
cracks.
8 - Replace burners making sure to fully engage on orifice.
Resecure burner mounting rail and flue box. Inspect flue
box gasket. Replace gasket if necessary.
9 - Slide heat exchanger into cabinet and reĆsecure heat
exchanger screws.
10 - Reinstall filler piece making sure that there is a good
seal between the cabinet sides, blower and deck and
filler piece. Use silicon caulking to fill in any potential
gaps.
11 - ReĆsecure flue pipe, gas piping and access panels.
12 - Carefully check all piping connections (factory and
field) for gas leaks. Use a leak detecting solution or othĆ
er preferred means.
12 - Turn on gas and electrical supply.

Page 20
FIGURE 25
HEAT EXCHANGER REMOVAL (unit shown in horizontal position)
REMOVE SCREWS (4)
SLIDE ENTIRE ASSEMBLY OUT OF CABINET Front
Right
Top
Bottom
Left
Back
CAUTION
Potential for gas leaks, fire or explosion.
Some soaps used for leak detection are corrosive
to certain metals. Carefully clean piping thorĆ
oughly after leak detection has been completed.
Can cause damage to piping resulting in gas
leaks, fire or explosion.
C-Supply Air Blower
1 - Check and clean blower wheel.
2 - Motors used on the Lennox 80UHG series units are
permanently lubricated and need no further luĆ
brication.
D-Flue and Chimney
Flue must conform to all AGA/GAMA enting requireĆ
ments. Flue pipe deteriorates from the inside out and must
be disconnected in order to check thoroughly. Check flue
pipe, chimney and all connections for tightness and to
make sure there is no blockage or leaks.
E-Electrical
1 - Check all wiring for loose connections.
2 - Check for correct oltage.
3 - Check amp-draw on blower motor.