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Electronic Ignition Models - Atwood 79 Series Service Manual

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FURNACE - ELECTRONIC IGNITION Model (continued)
CAUSE
S O O T I N G (caused by lazy yellow flame)
Low gas pressure
Low voltage
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Air leakage at gaskets
Combustion wheel installed backwards or loose
Blockage in heating chamber or burner head
Faulty motor
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Wrong vent kit or draft cap
FAN RUNS CONTINUOUSLY WITH THERMOSTAT "OFF"
Defective thermostat
Shorted thermostat leads
Defective relay
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LIMITING = BURNER CYCLING ON AND OFF - BLOWER RUNS CONSTANTLY WITH THERMOSTAT ON
Restricted or insufficient discharge ducting
Furnace over fired
Restricted return air supply
Defective limit switch
BLOWER SHUTS OFF AT SAME TIME BURNER SHUTS OFF
Wired wrong
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Faulty relay
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BLOWER VIBRATES OR IS NOISY
Motor mount loose
Damaged blower wheel
Motor shaft bent
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INSUFFICIENT HEAT
Furnace under fired
Furnace improperly sized for coach/or conditions
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Effective: 8/10/98
SOLUTION
*Set pressure to a minimum of 11˝ W.C. with all appliances
running. Replace regulator if not obtainable.
Correct power supply*
Replace gaskets
Reposition wheel and tighten.
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Clean or replace
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Replace motor
Replace with correct vent kit or draft cap
Replace thermostat
*Replace wire or wires
Replace relay
a. Ducting must meet furnace's minimum requirements.*
b. No excess ducting or unnecessary bends.*
c. All closeable registers must be fully open and unrestricted.*
Set gas pressure to a minimum of 11˝ W.C. with all appliances
running replace regulator, if not obtainable. Also, check main
burner orifice, it must comply with furnace's specifications.*
Make sure return air meets furnace minimum requirements.*
Replace limit switch
*Correct wiring
Replace relay.
Tighten motor mounting bracket
a. Ducting must meet furnace's minimum requirements*
b. No excess ducting or unnecessary bends.*
c. All closeable registers must be fully open and unrestricted.
Replace blower wheel.
Replace motor
1. Set gas pressure to 11˝ W.C. with all appliances running,
replace regulator if not obtainable. Also, check main burner
orifice, it must comply with furnace's specifications.
2. Check ducting and return air according to furnaces
specifications.*
Replace furnace with proper size.
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