Lennox F8AUH Series User manual

Page 1
Corp 9912−L5
Revised 08−2004
AFUE - Up to 80.5%
Heating Input - 45,000 to 120,000 Btuh (13.2 to 35.2 kW)
Add-On Cooling - 1 thru 5 Tons (3.5 to 17.6 kW)
F8AUH
Gas Furnaces
Up-Flow/Horizontal
SERVICE MANUAL
F8AUH series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
with tubular heat exchangers formed of aluminized steel.
F8AUH 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 LPG operation. F8AUH model
units are equipped with a hot surface silicon carbide ignition
system. The F8AUHX unit meets the California Nitrogen Ox-
ides (NOx) Standards and California Seasonal Efficiency re-
quirements. All units use a redundant gas valve to assure
safety shut−off as required by A.G.A. or C.G.A. Units may be
installed in upflow or horizontal position.
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 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Horizontal Venting 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Installation 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks 14. . . . . . . . . . . . . .
V Typical Operating Characteristics 16. . . . . . . . . . . . . .
VI Maintenance 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 19. . . . . . . . . . . .
VIII Control Board Troubleshooting Guide 23. . . . . . . .

Page 2
SPECIFICATIONS
Model No. F8AUH**−24−045
F8AUH**−24−045X F8AUH**−24−060 F8AUH**−36−060 F8AUH**−36−060X F8AUH**−24−075 F8AUH**−36−075 F8AUH**−36−075X
Input Btuh (kW) 45,000 (13.2) 60,000 (17.6) 60,000 (17.6) 75,000 (22.0) 75,000 (22.0)
Output Btuh (kW) 39,600 (10.8) 49,200 (14.4) 49,200 (14.4) 61,700 (18.1) 61,700 (18.1)
AFUE 80.1% 80.5% 80.5% 80.1% 80.0%
California Seasonal Efficiency 75.4% 76.4% 75.9% 76.8% 76.8%
Flue size connection dia. − in. (mm) round 3 (76) 3 (76) 3 (76) 4 (102) 4 (102)
Temperature rise range − _F (_C) 30 − 60 (17 − 33) 45 − 75 (25 − 42) 45 − 75 (25 − 42) 45 − 75 (25 − 42) 45 − 75 (25 − 42)
High static AGA/CGA cert. − in wg. (Pa) .50 (125) .50 (125) .50 (125) .50 (125) .50 (125)
Gas Piping Size IPS Nat. or LPG/propane 1/2 (13) 1/2 (13) 1/2 (13) 1/2 (13) 1/2 (13)
Blower wheel nominal in. 9 x 7 9 x 7 10 x 7 9 x 7 10 x 7
Blower
wheel
nominal
diameter x width mm 229 x 178 229 x 178 254 x 178 229 x 178 254 x 178
Blower motor output − hp (W) 1/4 (187) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224)
Nominal coolin
g
Tons 1, 1.5 or 2 1, 1.5 or 2 2, 2.5 or 3 1, 1.5 or 2 2, 2.5 or 3
Nominal
cooling
that can be added kW 3.5, 5.3 or 7.0 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6
Shipping weight − lbs. (kg) 1 package 130 (59) 130 (59) 135 (61) 135 (61) 135 (61)
Electrical characteristics 120 volts − 60 hertz − 1 phase (less than 12 amps) All models
OPTIONAL ACCESSORIES − Must Be Ordered Extra
Hanging Bracket Kit 46J66 46J66 46J66 46J66 46J66
High Altitude Pressure Switch Kits No Change No Change No Change 88J80 88J80
LPG/propane kit 38K84 38K84 38K84 38K84 38K84
Sidewall Power Venting Kit 79J15 79J15 79J15 79J15 79J15
Twinning Kit 15L38 15L38 15L38 15L38 15L38
Up−Flow/Horizontal Filter and Filter Rack Kits
No. & sizeoffilters− in. (mm)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
*Variable Field.
Annual Fuel Utilization Efficiency based on US DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating
for non−weatherized furnaces.
For proper operation at altitudes over 4500 ft. (1370 m).
Required for horizontal venting applications.
Polyurethane frame type filter is furnished with kit.

Page 3
SPECIFICATIONS
Model No. F8AUH**−48−075
F8AUH**−48−075X
F8AUH**−48−100
F8AUH**−48−100X
F8AUH**−60−100
F8AUH**−60−100X F8AUH**−48−120 F8AUH**−60−120 F8AUH**−60−120X
Input Btuh (kW) 75,000 (22.0) 100,000 (29.3) 100,000 (29.3) 120,000 (35.2) 120,000 (35.2)
Output Btuh (kW) 61,700 (18.1) 82,000 (24.0) 82,000 (24.0) 98,400 (28.8) 98,400 (28.8)
AFUE 80.0% 80.1% 80.0% 80.0% 80.1%
California Seasonal Efficiency 76.3% 76.5% 77.0% Not available 75.5%
Flue size connection dia. − in. (mm) round 4 (102) 4 (102) 4 (102) 4 (102) 4 (102)
Temperature rise range − _F (_C) 45 − 75 (25 − 42) 45 − 75 (25 − 42) 35 − 65 (19 − 36) 45 − 75 (25 − 42) 45 − 75 (25 − 42)
High static AGA/CGA cert. − in wg. (Pa) .50 (125) .50 (125) .65 (162) .50 (125) .50 (125)
Gas Piping Size IPS Nat. or LPG/propane 1/2 (13) 1/2 (13) 1/2 (13) 1/2 (13) 1/2 (13)
Blower wheel nominal in. 11 x 8 12 x 8 12 x 9 10 x 10 12 x 9
Blower
wheel
nominal
diameter x width mm 279 x 203 305 x 203 305 x 229 254 x 254 305 x 229
Blower motor output − hp (W) 1/2 (373) 1/2 (373) 3/4 (560) 1/2 (373) 3/4 (560)
Nominal coolin
g
Tons 2 thru 4 2 thru 4 3.5 thru 6 2 thru 4 3.5 thru 6
Nominal
cooling
that can be added kW 7.0 thru 14.1 7.0 thru 14.1 12.3 thru 21.1 7.0 thru 14.1 12.3 thru 21.1
Shipping weight − lbs. (kg) 1 package 140 (64) 175 (79) 175 (79) 175 (79) 175 (79)
Electrical characteristics 120 volts − 60 hertz − 1 phase (less than 12 amps) All models
OPTIONAL ACCESSORIES − Must Be Ordered Extra
Hanging Bracket Kit 46J66 46J66 46J66 46J66 46J66
High Altitude Pressure Switch Kits 88J80 18L24 18L24 18L24 18L24
LPG/propane kit 38K84 81J14 81J14 81J14 81J14
Sidewall Power Venting Kit 79J15 79J15 79J15 79J15 79J15
Twinning Kit 15L38 15L38 15L38 15L38 15L38
Up−Flow/Horizontal Filter and Filter Rack Kits
No. & sizeoffilters− in. (mm)
32J02 (single)
66K64 (ten)
(1) 16 x 20 x 1
(406 x 508 x 25)
46J14 (single)
66K65 (ten)
(1) 20 x 20 x 1
(508 x 508 x 25)
46J14 (single)
66K65 (ten)
(1) 20 x 20 x 1
(508 x 508 x 25)
46J14 (single)
66K65 (ten)
(1) 20 x 20 x 1
(508 x 508 x 25)
46J14 (single)
66K65 (ten)
(1) 20 x 20 x 1
(508 x 508 x 25)
*Variable Field.
Annual Fuel Utilization Efficiency based on US DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating
for non−weatherized furnaces.
For proper operation at altitudes over 4500 ft. (1370 m).
Required for horizontal venting applications.
Polyurethane frame type filter is furnished with kit.

Page 4
BLOWER DATA
F8AUH**−24−045, F8AUH**−24−060 AND F8AUH**−24−75 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High Medium−High Medium−Low 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 − 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
F8AUH**−36−060 AND F8AUH**−36−075 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High Medium−High Medium−Low 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 − 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
F8AUH**−48−075, F8AUH**−48−100 AND F8AUH**−48−120 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High Medium−High Medium Medium−Low 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 − 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 5
BLOWER DATA
F8AUH**−60−100 AND F8AUH**−60−120 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External
Static
Pressure High Medium−High Medium Medium−Low 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 − 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)

Page 6
HORIZONTAL VENTING REQUIREMENTS
(Requires Optional Side Wall Power Venting Kit)
Furnace
Model No
Vent Pipe Diameter
Furnace Connection
Vent Pipe Minimum
Equivalent Length
Vent pipe Maximum
Equivalent Length
Horizontal Venting
Transition Required
Model No. in. mm feet meters feet meters in. mm
F8AUH**−24−045
F8AUH**−24−060
F8AUH**−36−060 3 76 10 3.0 60 18.0 3 to 4 76 to 102
F8AUH**−24−075
F8AUH**−36−075
F8AUH**−48−075
F8AUH**−48−100
F8AUH**−60−100
F8AUH**−48−120
F8AUH**−60−120
4 102 10 3.0 60 18.0 − − − − − − − −
VENTING NOTES − Elbows − One 3 inch (76 mm) diameter 45_elbow is equivalent to 3 feet (1.0 m) of straight vent pipe.
One 4 inch (102 mm) diameter 45_elbow is equivalent to 4 feet (1.2 m) of straight vent pipe.
One 3 inch (76 mm) 90_elbow is equivalent to 5 feet (1.5 m) of straight vent pipe.
One 4 inch (102 mm) 90_elbow is equivalent to 7 feet (2.1 m) of straight vent pipe.
Two 45_elbows are equal to one 90_elbow.
Tees − One 3 inch (76 mm) diameter tee is equivalent to 19 feet (5.8 m).of straight vent pipe.
One 4 inch (102 mm) diameter tee is equivalent to 25 feet (7.6 m).of straight vent pipe.
Transition − 3 inch to 4 inch (76 mm to 102 mm) transition is equivalent to 2 feet (0.61 m) of straight vent pipe.
Transition furnished with power venter should be installed on top of flue adaptor at induced draft blower.
NOTE − All horizontal venting applications require optional Sidewall Power Venting Kit.
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. (1372m) 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 blower pressure switches are factory
set and are not to be adjusted.
At elevations of 4500 ft. (1372m) or greater, change factory
installed pressure switch to switch listed in table below.
UNIT MODEL PRESSURE SWITCH
PART NUMBER
F8AUH**−24−045(X) NO CHANGE
F8AUH**−24−060
F8AUH**−36−060(X) NO CHANGE
F8AUH**−24−075
F8AUH**−36−075(X)
F8AUH**−48−75(X)
88J80
F8AUH**−48−100(X)
F8AUH**−60−100(X) 18L24
F8AUH**−48−120
F8AUH**−60−120(X) 18L24

Page 7
FIGURE 1
BLOWER
ACCESS PANEL
HEAT EXCHANGER
ASSEMBLY
BURNER
ASSEMBLY
COMBUSTION AIR
BLOWER
CONTROL
BOARD
TRANSFORMER
PRESSURE
SWITCH
GAS VALVE
PRIMARY
LIMIT
BURNER
ACCESS PANEL
BLOWER
ASSEMBLY
F8AUH PARTS ARRANGEMENT
FIGURE 2
HEAT EXCHANGER
COMBUSTION AIR BLOWER
MANIFOLD
ROLLOUT SWITCH (2)
COMBUSTION AIR
PROVE SWITCH
GAS VALVE
BURNERS
COLLECTOR
PRIMARY LIMIT
Front
Right
Top
Bottom
Left
Back
HEATING COMPONENTS (shown in horizontal position)

Page 8
FIGURE 3
F8AUH BURNER ASSEMBLY (shown in upflow position)
Top
FLAME
SENSOR
MANIFOLD
ORIFICE
GAS VALVE
HEAT EXCHANGER
VEST PANEL
BURNER
UPPER
BURNER
MOUNTING
RAIL
LOWER
BURNER
MOUNTING
RAIL
BURNER
BOX
BURNER
BOX
TOP
Front Right
Bottom
Left
Back
PRIMARY LIMIT
ROLLOUT
SWITCHES
CARBIDE
IGNITOR
I−UNIT COMPONENTS (Figures 1, 2, 3)
F8AUH unit components are shown in figure 1. The gas
valve, combustion air blower and burners can be ac-
cessed by removing the burner access panel. Electrical
components are mounted to the blower housing.
F8AUH units are factory equipped with bottom return air pan-
els in place. The panels are designed to be field removed as
required for bottom air return. Knockout panels are provided
for side return air.
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace’s
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis-
charge by putting the furnace, the control and
the technician at the same electrostatic poten-
tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per-
forming any service procedure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
1− Control Transformer (T1)
A transformer located on the blower housing provides
power to the low voltage 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 se-
ries with line voltage. When the blower door is removed 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, sim-
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.

Page 9
3− Furnace Control (A3)
All F8AUH model units are equipped with an integrated
ignition blower control (50A55), which controls ignition,
safety circuits, blower operation, fan off timing and allows
for thermostat connection and troubleshooting. The sys-
tem consists of ignition control board (figure 6 with control
terminal designations in table 4) and a silicon carbide ig-
nitor (figure 7). The board features two LED lights for
troubleshooting and two accessory terminals rated at (4)
four amps. See table 3 for troubleshooting diagnostic
codes. Table 1 and 2 show jack plug terminal designa-
tions. Units equipped with this control board board can be
used with either electronic or electro−mechanical thermo-
stats without modification. Each time power is applied to
the furnace, the control board board performs a selfcheck
including energizing the combustion air blower for a peri-
od of 1 second.
TABLE 1
CONTROL BOARD J156 (J2) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1Combustion Air Blower Line
2Ignitor Line
3Combustion Air Blower Neutral
4Ignitor Neutral
TABLE 2
CONTROL BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1High Limit Out
2Not Used
324V
4Not Used
5Rollout Switch In
624V
7High Limit In
8Ground
9Gas Valve In
10 Pressure Switch In
11 Rollout Switch Out
12 Gas Valve Out
a−Electronic Ignition (See Figure 5)
On a call for heat the 50A55 control board monitors the
combustion air blower pressure switch. The control will not
begin the heating cycle if the pressure switch is closed (by−
passed). Once the pressure switch is determined to be
open, the combustion air blower is energized. When the
differential in the pressure switch is great enough, the
pressure switch closes and a 15−second pre−purge be-
gins. If the pressure switch is not proven within 2−1/2 min-
utes, the control goes into Watchguard−Pressure Switch
mode for a 5−minute re−set period.
After the 15−second pre−purge period, the carbide ignitor
warms up for 11 to 21 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. If ignition is not proved during the 4−second period,
the control will try four more times with an inter purge and
warm−up time between trials of 37 seconds. After a total 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.
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 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 individu-
al 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 10
The 50A55 control 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 12L42: Limit must close within
5 trials for ignition or board goes into one hour limit Watchguard. Units with board
56L85: 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.
ALTERNATING SLOW
FLASH
ALTERNATING 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 .7 microAmps. Replace flame sense rod.
ALTERNATING FAST
FLASH
ALTERNATING 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 flame sense current < 0.15 microAmps
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
DEMAND
CAB
GAS VALVE
15
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
ÉÉ
40
ÉÉÉÉÉÉÉÉ
IGNITOR
36
1
Pre -Purge Ignitor Warmup Trial for
Ignition
Post
Purge
5 SEC82
*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
50A55 Control Board Ignition Sequence
37