Lennox F8AUH Series Service Manual Download | Manualshive

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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 SEC

82

*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

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Summary of Contents for F8AUH Series

Page 1: ...e 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 rep...

Page 2: ...r 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...

Page 3: ... 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 pr...

Page 4: ...5 795 375 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 ...

Page 5: ...125 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 ...

Page 6: ...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 sett...

Page 7: ...R 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: ... 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 ...

Page 9: ... 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 go...

Page 10: ...er 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 Mea...

Page 11: ...tive Make sure that the furnace is wired 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 U...

Page 12: ...ocated over the rightmost burner The limit is a N C SPST manual reset limit con nected in series with the ignition control A3 When S47 senses rollout the ignition control immediately stops igni tion and closes the gas valve If unit is running and flame rollout is detected the gas valve will close and ignition con trol will be disabled Rollout can be caused by a blocked flue or lack of combustion a...

Page 13: ...ion air blower housing by means of a flexible silicone hose It monitors air pressure in the combustion air blower housing The switch is a single pole single throw pressure switch electrically connected to the furnace control The purpose of the switch is to prevent burner operation if the combus tion air blower is not operating or if the flue becomes ob structed FIGURE 15 PROVE SWITCH COMBUSTION AI...

Page 14: ...vice techni cian or gas supplier Turning Off Gas To Unit 1 Set thermostat to lowest setting 2 Turn off all electrical power to unit if service is to be performed 3 Remove access panel 4 Switch lever on White Rodgers gas valve to OFF turn knob on Honeywell valve clockwise to OFF Do not force 5 Replace access panel C Safety or Emergency Shutdown Turn off unit power Close manual and main gas valves D...

Page 15: ...LVE REGULATION 3 5 0 0 3 Natural L P 9 5 0 5 Unit Fuel The gas valve is factory set and should not require adjustment All gas valves are factory regulated See table 6 See specifica tions section of this manual for High Altitude manifold pressure settings Manifold Adjustment Procedure 1 Connect a test gauge to outlet pressure tap on gas valve Start unit and allow 5 minutes for unit to reach steady ...

Page 16: ...ICS A Blower Operation and Adjustment NOTE The following is a generalized procedure and does not apply to all thermostat controls 1 Blower operation is dependent on thermostat control system 2 Generally blower operation is set at thermostat sub 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 ...

Page 17: ...ion 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 crimps designed in the heat exchanger cleaning is not recommended Removal is for inspection only NOTE...

Page 18: ...esulting in gas leaks fire or explosion C Supply Air Blower 1 Check and clean blower wheel 2 Motors used on the F8AUH series units are perma nently lubricated and need no further lubrication D Flue and Chimney Flue must conform to all AGA GAMA venting require ments Flue pipe deteriorates from the inside out and must be disconnected in order to check thoroughly Check flue pipe chimney and all conne...

Page 19: ...hguard Pressure Switch delay Once S18 closes a 15 se cond pre purge follows 4 Control board energizes ignitor An 11 to 21 second warm up period begins 5 Gas valve opens for a 4 second trial for ignition igni tor will remain energized for the first second 6 Flame is sensed gas valve remains open for the heat call 7 After 45 second delay control board energizes in door blower B3 8 When heat demand i...

Page 20: ... LED 1 ON LED 2 SLOW FLASH SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES GAS VALVE OFF COMBUSTION AIR BLOWER ON INDOOR BLOWER ON HEATING SPEED LED 1 SLOW FLASH LED 2 OFF GAS VALVE OFF COMBUSTION AIR BLOWER OFF INDOOR BLOWER OFF WITH DELAY LED 1 OFF LED 2 SLOW FLASH Sequence holds until pressure switch closes or thermostat resets control NO NO YES NO NO NO IS COMBUSTION AIR BLOWER ENERGIZED HAS COMBUS...

Page 21: ...OD YES FLAME STABILIZATION PERIOD GAS VALVE OFF COMBUSTION AIR BLOWER ON INDOOR BLOWER OFF HAS CONTROL FAILED TO SENSE FLAME FOR FIVE CONSECUTIVE TRIES DURING A SINGLE HEAT DEMAND WATCHGUARD MODE GAS VALVE OFF COMBUSTION AIR BLOWER OFF INDOOR BLOWER OFF WITH DELAY LEDs SIGNAL WATCHGUARD FAILURE CODE IS 60 MINUTE RESET PERIOD COMPLETE YES 4 SECONDS YES HAS CONTROL RESET IGNITION SEQUENCE FOUR TIMES...

Page 22: ...H CLOSED CHECK FOR MAIN BURNER FLAME SENSE IS MAIN BURNER FLAME OFF LED SLOW FLASH RATE REMAINS UNCHANGED THROUGHOUT COOLING CYCLE THERMOSTAT CALLS FOR COOLING COMPRESSOR CONTACTOR AND SYSTEM FAN ENERGIZED WITH 0 SECOND DELAY COOLING SPEED EAC H TERM ENERGIZED COMPRESSOR OFF THERMOSTAT OPENS SYSTEM FAN AND ACC TERM OFF WITH 0 SECOND DELAY NO GAS VALVE OFF COMBUSTION AIR BLOWER ON INDOOR BLOWER ON ...

Page 23: ...lly reset the roll out switch by pushing the top button ACTION 2 Determine the cause of the roll out switch activation before leaving furnace code LED 1 O 1 2 2 Roll out switch failure ACTION 1 Check continuity across roll out switch Replace roll out switch if switch is reset but does not have continuity LED 1 On LED 2 Slow Flash 1 2 3 Miswiring or improper connections at ACTION 1 Check wiring con...

Page 24: ... Fast Flash LED 2 Alternating Fast Flash 2 1 2 Broken or failed ignitor ACTION 1 Unplug ignitor and read resistance across ignitor If resistance does not read be tween 10 9 and 19 7 ohms replace the ignitor PROBLEM 3 UNIT FAILS TO FIRE IN THE HEATING MODE COMBUSTION AIR BLOWER DOES NOT ENERGIZE Condition Possible Cause Corrective Action Comments 3 1 Unit operates with a cooling or con tinuous fan ...

Page 25: ...bing with a heating demand Diagnostic lights flash the pressure switch failure code 2 5 minutes after heating demand 4 1 2 Pressure switch does not close due to obstructions in the pressure tub ing ACTION 1 Remove any obstructions from the pressure tubing and or taps LED 1 Off LED 2 Slow Flash 4 1 3 Pressure switch tubing damaged ACTION 1 Check pressure switch tubing for leaks Replace any broken t...

Page 26: ...prior to satisfying T stat demand Diagnostic lights flash the pressure switch code LED 1 Off LED 2 Slow Flash 6 1 1 Low pressure differential at the pres sure switch ACTION 1 Check for restricted vent inlet or ex haust Remove all blockage ACTION 2 Check for proper vent sizing See installation instructions 6 2 Combustion air blower energizes with a heating demand B li ht b t f il t t lit 6 2 1 Sens...

Page 27: ... heat exchanger ACTION 1 Check for sooting deposits or other restrictions in the heat exchanger assembly Clean assembly as outlined in instruction manu al ACTION 2 Check for proper combustion and flow CO2 should measure between 6 0 and 8 0 for natural and 6 5 and 8 5 for L P CO should measure below 04 400PPM in an air free sample of flue gases 6 3 4 Burners are not properly located in the burner b...

Page 28: ...contaminated ACTION 1 Check sense rod for contamination or coated surface Clean the sense rod with steel wool or replace sensor DO NOT USE SAND PA PER TO CLEAN ROD SAND PAPER WILL CONTRIBUTE TO THE CONTAMINATION PROBLEM PROBLEM 8 INDOOR BLOWER FAILS TO OPERATE IN COOLING HEATING OR CONTINUOUS FAN MODE Condition Possible Cause Corrective Action Comments 8 0 Indoor blower fails to operate in continu...

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