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Service/Review...
Rule # 1:
Use the KISS Principle!
Service/Review...
Rule # 1:
Keep
It
Simple
Stupid
Start with the BASICS!
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Assume nothing, check everything, no
matter how unrelated it may seem.
Forget everything that’s been done in
the past service calls.
Check low voltage connections, check
line voltage connections. Check voltages.
Check pressures, cycle it on the
thermostat. Cycle it on the safeties.
Drop out a motor.
Start with the BASICS!
(con”t)
Wiggle wires, jiggle connections and
look everywhere.
 Ignore your urges, remember that
the last guy did what you’re
considering and look how productive
that was.
 What are you looking for? - Won’t
know until you find it!
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SELF DIAGNOSTIC
FEATURE
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The IFC tests for internal & external faults
before allowing a heating sequence to begin.
The external check includes all safety devices &
pressure switches, making certain that they are in
their proper normally open or closed position. 24
volt signal leaves HLO to HLI to check limits &
PS/PS1 for pressure switch.
If a fault is detected the IFC will immediately
enter into a fault mode and flash the LED
according to the fault detected.
(Red Book-Page 9)
SELF DIAGNOSTIC
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The IFC will remain in the fault mode until the
problem is corrected. Once the fault is cleared,
the IFC will start the heating sequence as long as
the call for heat still exists.
The IFC has expanded diagnostic features that
monitors the system. If a fault is detected , the
IFC will de-energize the gas valve & flash the LED.
The control will automatically reset a lock-out due
to loss of flame, see IFC table page 10 reset time.
(Red Book-Page 9)
SELF DIAGNOSTIC
SERVICE CALL
 IMPORTANT: Do not remove blower
door or turn off power before
checking flash rate LED. Sight glass
is provided on upflow models in the
blower door panel. (Pre W4, series
furnaces)
 Note LED flash rate timing.
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(Red Book-Page 9)
Diagnostic Code Label
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Flashing Slow one/ sec
Flashing Fast two/sec
Continuous On
Continuous Off
2 Flashes *
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
Normal, No Call
Call for Heat
Replace Control
Check Power
External Lockout
Inducer / Pr. Switch Error
Open Thermal Limit Switch
Flame Sensed w/o GV On
Ground, Polarity, Low Volts
Gas Valve Circuit Error
Low Flame Sense Signal
Open Igniter
Improper Ground
Low Voltage
Faulty Triac
More Than 10 Volts Between Neutral and Ground
 Flash Rate 1/4 sec on and 1/4 sec off, with 2 sec Pause Between Groups of Flashes
SELF DIAGNOSTIC
FEATURE
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CONTINUOUS ON - internal fault, or
grounded sensor. Turn power off & on before
replacing, may work OK.
2 FLASH - System lockout - no flame. See 1
3 FLASH - Pressure switch error.
4 FLASH - TCO (limit) open.
5 FLASH - Flame sensed with gas valve deenergized, (stuck open)
(Red Book-Page 9)
Fault Diagnostics - 2 FLASH
System lockout (loss of flame)
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BAD GROUND
(power)
LOOSE GROUND
(wire or burner)
WRONG GAS
PRESSURE
BAD HOT SURFACE
IGNITOR
DIRTY SENSOR
BAD SENSOR
NO GAS
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CHECK ALL
CONNECTIONS
SET WITH WATER
MANOMETER
OHM OUT REPLACE
IF BAD
CHECK  amp
SIGNAL
REPL. IF BAD
GAS SUPPLY, SHUT
OFF, GAS VALVE
(Red Book-Page 11)
MICROAMP SIGNAL
 If you are getting call backs w/ two flash
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and have measured good  amp signal check
ground wire.
MUST BE DIRECT FROM UNIT TO PANEL
BOX.
Also check burner closet to flame rod for
good clean tight connection.
MICRO AMP METER HOOK UP
HOOK UP METER IN SERIES
(Red Book-Page 25)
LOCKOUT - 2 FLASH
A momentary loss of gas supply,
flame blowout, or a shorted or open
flame sensor will be sensed within
.7 seconds during normal heating
cycle.
 When a system lockout occurs, the
IFC de-energizes the gas valve,
energizes the inducer motor and
indoor blower to heat speed.
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(Red Book-Page 11)
Flame Sensing - Variables
Remember Ohms Law E=I x R
 Watch that resistance
 Too little DC = too bad
 Too much AC = too bad
 Grounded flame sensor
 Look out for noise!
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Increased Circuit Resistances
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Burner oxidation
Non-secure burner
Flame “lift off”
Loose wire connections
Contaminated flame sensor
Faulty grounds
No grounds
Reverse polarity
Fault Diagnostics - 3 FLASH
Single Stage
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Bad vent system - improper draft, flue
pipe or chimney blocked or plugged.
Bad venter motor or fan dirty.
Heat exchanger plugged or cracked.
90% units PVC not supported or pitched
correctly back towards unit.
?? Maybe a bad pressure switch.??
A draft gauge or incline needed for
testing.
(Red Book-Page 11)
Fault Diagnostic - 3 FLASH
Two Stage and Variable Speed
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Blocked condensate drain
90% - 30 second off to drain condensate
Inducer starts on hi speed then goes to low
If 2nd stg PS after 3 min delay IFC
restarts unit and run for 10 min. If 2nd stg
PS still dose not close after 10 min IFC will
start cycle again as long as there is a call
for 2nd stage heat at thermostat.
(Red Book-Page 12)
3 FLASH - cont.
Variable Speed / TUY-R-A
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If 1st stg PS opens during 1st stg call for
heat, gas valve is de-energized and inducer
will go to hi speed for 10 min. If PS closes
during 10 min the IFC will restart ignition
sequence. If PS dose not close the inducer
will be energized to hi again and continue
cycle as long as 1st stg heat is calling.
2nd stg operation is same as page 12.
(Red Book-Page 13)
Fault Diagnostic - 4 FLASH
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Thermal Protection Devices Open
TCO limit, aux.. limit, flame roll out, bad
indoor blower motor, wrong motor speed,
90% units inducer limit (155’F open),
burner box manual reset limit.
If TCO is open check temperature rise
through unit, check specs on unit label.
(Red Book-Page 13)
Fault Diagnostic-5 FLASH
Flame sensed without a call for heat
or when gas valve is de-energized.
The IFC will energize indoor blower
to run on heating speed.
 The system goes into lockout and will
not be reset until this fault is
corrected.
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(Red Book-Page 13)
IFC Quick Reference
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YOU MUST HAVE:
SERVICE TIPS
Volt/OHM Meter with
micro amp scale A
Water Manometer
Incline Manometer
with a 0 - 2” range
Dwyer #1227 good
Pocket Thermometer
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IFC requires 1.0A
minimum flame signal
80&90% single stage
1.8-3.0 
80&90% two stage
1st stg 1.2-1.8 A 
2nd stg 2.3-3.0A 
A good procedure is to
check A signal B4
cleaning and after
(Red Book-Page 20)
Radiant Sense Ignition Controls
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Radiant sense was used for a short time on
TUE Trane units. The control system is no
longer used. There are six different
versions how to identify see pages 39-40.
Page 41 shows sensor and correct position
of hot surface ignitor.
The rest of the pages are sequence of
operation and wiring schematics. Use as
needed.
(Red Book-Pages 39-49)
Troubleshooting Procedures
If the LED on the IFC is on
continuously, the fault is internal to
the IFC. To make sure, interrupt line
voltage for a few seconds and then
restore. If internal fault is indicated
again, and flame sensor is not shorted
to ground, replace control.
 Note caution on five flash fault.
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(Red Book-Page 50)
Troubleshooting Procedures
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Flow charts for controls 50A50, 50A51,
and 50A52. Page numbers are off by two,
49=51, 50=52, 51=53 etc. correct now.
50A50 flame sensor fault (2 flash) what
chart and page do we go to??
Page 55, chart 5a - 5p
Lets do it.
Pages 51 - 64 flow charts.
(Red Book-Page 50)
Service/Review...
Observe...
 Ask questions…
 Observe…
 Check Fault Codes...
 Check equipment / proper sequence
of operation, etc...
 Proper tools!
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Installation/Service
(Review)
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Things We Need To Get Better At:
Gathering Information from the consumer.
Looking beyond the failure in front of us, why
did it fail. Shit does not just happen!
Running the system long enough to stabilize:
Checking your temperature rise or subcooling and
superheat.
Remember - Over 50% of the electronic controls
replaced, did not need to be replaced.
Sample Service TicketWHAT’S WRONG?