1. Furnace Troubleshooting

2. Combustion Service

3. Objectives : Good furnace troubleshooting requires enhanced skills from the servicer
Service Tips
Induced draft furnace combustion process
Combustion system service checks
System effects on draft
Flame detection - principles and service checks
Flame sensing variables

4. Service Tip Use of diagnostic LED 40” Furnace “book” (p.9)
After introducing the visual, cut to first video segment showing
First check of thermostat call for heat
“Don’t Touch That Dial”!!!
Approach furnace
Check LED Flash Rate
- Wide shot
- Close up of light flashing (2 flash rate)
Next:
PPT: Different flash rates (front cover of control)
PPT: Bullet Slide “Pressure switch error”

5. Service Tip Use of diagnostic LED (40” Furnace “book” (p.9)
DON’T TOUCH THAT DIAL !!
After introducing the visual, cut to first video segment showing
First check of thermostat call for heat
“Don’t Touch That Dial”!!!
Approach furnace
Check LED Flash Rate
- Wide shot
- Close up of light flashing (2 flash rate)
Next:
PPT: Different flash rates (front cover of control)
PPT: Bullet Slide “Pressure switch error”

6. Error Flash Codes R W1 W2 Y R G B WHITE-RODGERS Emerson Electric Co.
DIAGNOSTIC INDICATOR
FLASHING SLOW NORMAL, NO CALL FOR HEAT
FLASHING FAST NORMAL CALL FOR HEAT
CONTINUOUS ON REPLACE CONTROL
CONTINUOUS OFF CHECK POWER
2 FLASHES SYSTEM LOCKOUT (NO FLAME)
3 FLASHES PRESSURE SWITCH PROBLEM
4 FLASHES THERMAL PROTECTION DEVICE OPEN
5 FLASHES FLAME SENSED WITH GAS VALVE OFF
REFER TO SERVICE INSTRUCTIONS FOR MORE INFORMATION FP
PS2
MVH
HLI TH
GND
PS1
MVL MV
COM TR
HLO
WHITE-RODGERS Emerson Electric Co. R WR
MODEL 50A D340021P01
REPLACE WITH
CNT 1308
Green wall PPT of latest IFC cover. Scanned is good if good quality.
Go through the flash rates 1 by 1, quickly
Transition to “Let’s look at 2 of the most common errors” - first of which is a flame sense error - commonly called a 2 flash lockout.
Flame sensing error

7. Error Flash Codes (See p. 9)
WHITE-RODGERS Emerson Electric Co. WR
MODEL 50A D340021P01
REPLACE WITH
CNT 1308
DIAGNOSTIC INDICATOR
FLASHING SLOW NORMAL, NO CALL FOR HEAT
FLASHING FAST NORMAL CALL FOR HEAT
CONTINUOUS ON REPLACE CONTROL
CONTINUOUS OFF CHECK POWER
2 FLASHES SYSTEM LOCKOUT (NO FLAME)
3 FLASHES PRESSURE SWITCH PROBLEM
4 FLASHES THERMAL PROTECTION DEVICE OPEN
5 FLASHES FLAME SENSED WITH GAS VALVE OFF
REFER TO SERVICE INSTRUCTIONS FOR MORE INFORMATION FP
PS2
MVH
HLI TH
GND
PS1
MVL MV
COM TR
HLO R
W1 W2 Y R G B
Green wall PPT of latest IFC cover. Scanned is good if good quality.
Go through the flash rates 1 by 1, quickly
Transition to “Let’s look at 2 of the most common errors” - first of which is a flame sense error - commonly called a 2 flash lockout.
Flame sensing error

8. Pressure Switch Error
What can cause the Integrated Furnace Control to indicate a pressure switch error?
(Flowchart on p. 51 of 40” Furnace “Book”)
Need video of 3 flash from location

9. Pressure Switch Single Stage
INTEGRATED FURNACE CONTROL 6 3 9 12 4 5 10 7 11 1 2 8 Y W G R C
FLAME
SENSOR
TCO
TCO-B
FUSE LINK
PRESSURE
SWITCH 1,
GAS VALVE TR TH MV PS
HLI
HLO FP
GND

10. Pressure Switch Two Stage
INTEGRATED FURNACE CONTROL 2 7 11 8 12 6 10 9 1 3 5 4 Y W G R
FLAME
SENSOR
TCO
TCO-B
FUSE LINK
PRESSURE SWITCH
1ST STAGE B
COM CL HI LO
2ND STAGE
GAS VALVE
THERMOSTAT
TWINNING FP
HLO
HLI
PSI
GND
MVL
MVCOM
MVH
PS2 TH TR

11. Inducer Motor IFC Y W G R B 9 1 3 5 4 FLAME SENSOR TCO TCO-B FUSE LINK
PRESSURE SWITCH
1ST STAGE B 2
COM CL HI LO
THERMOSTAT
TWINNING FP
HLO
HLI
PSI
GND
IGN N
IND N
IND LO
IND HI
IGN
IGNITOR
IND.
MTR.

12. Pressure Switch Error What can cause the integrated furnace control to
indicate a pressure switch error?
Switch CLOSED when it should be OPEN
24 VAC at “PS” too early (inducer not “energized)
(See Flowchart on p.51 of 40” Furnace “Book”)
When referencing the 40” furnace book - ask audience not to try to completely examine the flowchart - it’s there for future reference.
Mention that they start on P.49 with the 1 stg IFC first

13. Pressure Switch Error What can cause the integrated furnace control to
indicate a pressure switch error?
Switch OPEN when it should be CLOSED
No 24 VAC at “PS”, inducer circuit “energized”
(See Flowchart on p.51 of 40” Furnace “Book”)
When referencing the 40” furnace book - ask audience not to try to completely examine the flowchart - it’s there for future reference.
Mention that they start on P.49 with the 1 stg IFC first

14. Pressure Switch Error Diagnostics
Vent Length
Draft/Vacuum Measurements
Electrical Checks
Factors Affecting Draft

15. Determining Total Vent Lengths See p. 9 of Installer Guide 18-CD19D6-5
MAXIMUM VENT LENGTH:
MAXIMUM TOTAL EQUIVALENT FEET
FOR VENT AND INLET AIR (See Notes)
MODEL
2” PIPE
& FITTINGS
2-1/2” PIPE
3” PIPE
*UX040C924
*UX060C936
*UX080C942
*UX100C948
*UX100C960
*UX120C960 60 30
N/A 80 15
100
NOTES: First Letter may be “A” or “T”
1. DO NOT MIX PIPE DIAMETERS IN THE SAME LENGTH
OF PIPE OUTSIDE THE FURNACE CABINET
(except adapters at top of furnace).
2. MAXIMUM PIPE LENGTHS MUST NOT BE EXCEEDED
3. One 90 o elbow is equivalent to 10 ‘ of 3 “ pipe 71/2’ of 21/2”
pipe, & 5’ of 2” pipe. Two 45o elbows equal one 90o elbow.
4. The termination tee or bend must be included in the total number of
elbows. The BAYVENT100A termination is equal to 5 equivalent
feet of pipe. The BAYVENT200A is 0 equivalent feet.
5. Pipe adapters are field supplied.
Use Vent Table from TUC Installer Guide
Prepare to answer many call in questions about this one.

16. Combustion Air Pressure Switch
FIELD SUPPLIED TUBE & TEE SECTION

17. Examine the effects of system variations on draft
Vent Length
Blockages
Wind
Gas Input
Airflow

18. Vacuum / Draft Pathway PRESSURE DIFFERENTIAL SWITCH BURNER INDUCED BOX
INLET PIPE
BURNER
BOX
PRIMARY HEAT EXCHANGER
FLUE COLLECTOR BOX
TRANSFER
TUBE
RECOUP
CELL
PRESSURE DIFFERENTIAL
SWITCH
INDUCED
DRAFT
BLOWER

19. Effects of Low System Airflow on Internal Vacuum
Hot furnace
Means hot flue gases
Hot flue gases expand - take up more space
Expanding flue gases raise pressure in furnace

20. Flame Current

21. Flame Rectification Ref p.25 of 40” Furnace “Book”
Remember Ohm’s Law
E = I X R

22. Basic Electrical Circuit
SOURCE - +
CONDUCTOR
CONTROL
LOAD

23. Alternating Current Sine Wave
Applied AC voltage + -

24. Flame Rectification circuit
What devices are used for electrodes?
Flame rod
Burner

25. Flame Rectification Circuit
Voltage Source: Ignition Control
“Load”: flame sensing circuit inside the control
Conductors: wires, and electrodes already identified.
“Switch”?
The flame completes the circuit.

26. Flame Sense Circuit
One electrode is larger than the other causing electron flow to be greater in one direction than in the other.
Compare the burner size to the flame rod size.

27. Flame Sensing - Service
Measuring outputs
Measuring inputs
Circuit integrity checks
Polarity
Grounding method / continuity

28. + FP
GND _
Current flow when flame rod
is positive + -
5a

29. _ FP
GND +
Current flow when flame rod
is negative + -
1a

30. Effective Flame Signal+ +
a
Effect = 4a pulsating DC
Applied AC voltage -
a -

31. Flame Rectification Circuit
Remember Ohm’s Law ?
What happens in a circuit if resistance increases and voltage stays the same?
What can affect the resistance in the circuit?
What else can affect the flame signal?

32. Increased circuit resistances
Burner oxidation
Non-secure burner
Flame “lift off”
Loose wire connections
Contaminated flame sensor
Faulty grounds
No grounds
Reverse polarity

33. DC Current vs. AC Current
VALVE DROPOUT IS IN AC MICROAMPS

34. DC Current vs. AC Current
50A STG CONTROL

35. DC Current vs AC Current 2 Stage IFC

36. 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!

37. Question
Name something which can cause a “2 flash” lockout which has not yet been discussed.
Answer:
1) No gas available - check supply
2) Multiple recycles caused by other faults (ie: pressure switch trips) (See p.10)
While waiting for questions - cue up 3 flash video