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Furnace Troubleshooting. Combustion Service. 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

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objectives good furnace troubleshooting requires enhanced skills from the servicer
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
service tip
Service Tip
  • Use of diagnostic LED
    • 40” Furnace “book” (p.9)
service tip5
Service Tip
  • Use of diagnostic LED

(40” Furnace “book” (p.9)

DON’T TOUCH THAT DIAL !!

error flash codes

WHITE-RODGERS Emerson Electric Co.

WR

MODEL 50A51 - 405 D340021P01

REPLACE WITH

CNT 1308

FP

MVH

PS2

HLI

TH

GND

R

MV

COM

TR

MVL

PS1

GND

HLO

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

W1W2 Y R G B

Error Flash Codes
error flash codes see p 9

WR

FP

MVH

PS2

HLI

TH

GND

MV

COM

TR

MVL

PS1

GND

HLO

Error Flash Codes(See p. 9)

WHITE-RODGERS Emerson Electric Co.

MODEL 50A51 - 405 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

R

W1W2 Y R G B

pressure switch error
Pressure Switch Error
  • What can cause the Integrated Furnace Control to indicate a pressure switch error?

(Flowchart on p. 51 of 40” Furnace “Book”)

pressure switch single stage

INTEGRATED FURNACE CONTROL

TR

6

TH

3

GAS VALVE

9

MV

2

1,

3

MV

12

4

PRESSURE

SWITCH

5

FUSE LINK

TCO

PS

10

HLI

7

11

FUSE LINK

TCO-B

1

HLO

FP

2

FLAME

SENSOR

8

GND

G

R

C

Y

W

Pressure SwitchSingle Stage
pressure switch two stage

INTEGRATED FURNACE CONTROL

TR

2

TH

7

GND

11

PRESSURE SWITCH

2ND STAGE

PS2

8

GAS VALVE

MVH

3

12

MVCOM

2

6

MVL

1

10

PRESSURE SWITCH

1ST STAGE

GND

9

FUSE LINK

TCO

PSI

1

HLI

3

FUSE LINK

TCO-B

HLO

5

FP

4

FLAME

SENSOR

COM

LO

R

G

B

W

W

Y

CL

HI

1

2

THERMOSTAT

TWINNING

Pressure SwitchTwo Stage
inducer motor

IGN

1

IND HI

2

IND.

MTR.

IND LO

3

IFC

IND N

4

IGNITOR

IGN N

5

PRESSURE SWITCH

1ST STAGE

GND

9

FUSE LINK

TCO

PSI

1

HLI

3

FUSE LINK

IFC

TCO-B

HLO

5

FP

4

FLAME

SENSOR

COM

LO

R

G

B

W

W

Y

CL

HI

1

2

THERMOSTAT

TWINNING

Inducer Motor
pressure switch error12
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”)

pressure switch error13
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”)

pressure switch error diagnostics
Pressure Switch Error Diagnostics
  • Vent Length
  • Draft/Vacuum Measurements
  • Electrical Checks
  • Factors Affecting Draft
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)

2” PIPE

& FITTINGS

2-1/2” PIPE

& FITTINGS

3” PIPE

& FITTINGS

MODEL

*UX040C924

*UX060C936

*UX080C942

*UX100C948

*UX100C960

*UX120C960

60

60

60

30

30

N/A

80

80

80

80

80

15

100

100

100

100

100

60

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.

Determining Total Vent LengthsSee p. 9 of Installer Guide 18-CD19D6-5
examine the effects of system variations on draft
Examine the effects of system variations on draft
  • Vent Length
  • Blockages
  • Wind
  • Gas Input
  • Airflow
vacuum draft pathway

PRESSURE DIFFERENTIAL

SWITCH

BURNER

BOX

PRIMARY HEAT EXCHANGER

INLET PIPE

TRANSFER

TUBE

RECOUP

CELL

FLUE COLLECTOR BOX

Vacuum / Draft Pathway

INDUCED

DRAFT

BLOWER

effects of low system airflow on internal vacuum
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

basic electrical circuit
Basic Electrical Circuit

SOURCE

-

+

CONDUCTOR

CONTROL

LOAD

alternating current sine wave

+

+

+

Applied AC voltage

-

-

Alternating Current Sine Wave
flame rectification circuit
Flame Rectification circuit

What devices are used for electrodes?

  • Flame rod
  • Burner
flame rectification circuit25
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.
flame sense circuit
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.
flame sensing service
Flame Sensing - Service
  • Measuring outputs
  • Measuring inputs
  • Circuit integrity checks
    • Polarity
    • Grounding method / continuity
slide28

5a

+

0

-

+

FP

GND

_

Current flow when flame rod

is positive

slide29

1a

+

0

-

_

FP

GND

+

Current flow when flame rod

is negative

effective flame signal
Effective Flame Signal

+

+

a

Effect = 4a pulsating DC

Applied AC voltage

-

-

a

flame rectification circuit31
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?

increased circuit resistances
Increased circuit resistances
  • Burner oxidation
  • Non-secure burner
  • Flame “lift off”
  • Loose wire connections
  • Contaminated flame sensor
  • Faulty grounds
  • No grounds
  • Reverse polarity
dc current vs ac current
DC Current vs. AC Current

VALVE DROPOUT IS IN AC MICROAMPS

dc current vs ac current34
DC Current vs. AC Current

50A50 1 STG CONTROL

flame sensing variables
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!
question
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)