STEP
ACTION
YES
NO
GO TO
18.
Turn power off.
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—
19
19.
Do you have continuity across the following connections?
• PL1-1 and BLUE wire at gas valve GV.
• PL1-10 and GREEN wire at gas valve GV.
13
20
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20.
The BLUE or GREEN wire from 2-stage furnace control to gas valve GV is not
making a good connection. Repair wire(s) or replace harness.
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—
8
21.
Does gas valve open and allow gas to flow?
24
22
—
22.
Are all manual gas cocks in ON position?
23
15
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23.
Replace gas valve.
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—
8
24.
Do main burners ignite?
26
25
—
25.
Check for the following:
• Inadequate flame carryover or rough ignition.
• Low inlet gas pressure.
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—
15
26.
Do main burners stay on?
36
27
—
27.
Turn power off and disconnect jumper across R and W/W1 thermostat termi-
nals.
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—
28
28.
Connect a DC microammeter in series with flame sensor wire.
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—
29
29.
Turn power on. Jumper R and W/W1 thermostat terminals.
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30
30.
Is DC current below 0.5 microamps?
32
31
—
31.
Check connections and retry. If current is near typical value and control will not
stay on, replace 2-stage furnace control. Current is typically 4.0 to 6.0 micro-
amps.
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—
8
32.
Clean flame sensor with fine sandpaper and recheck current. Current is typically
4.0 to 6.0 microamps.
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—
33
33.
Is current near typical value?
35
34
—
34.
Replace electrode.
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—
8
35.
Will main burners ignite and stay on?
8
13
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36.
Do you have burner pulsations?
37
38
—
37.
Check the following:
• Inadequate flame carryover.
• Low inlet gas pressure.
• Proper vent sizing for installation.
• Poor gas valve regulation.
• Leakage in, or around heat exchanger.
• Leakage in collector box.
• Leakage between inducer and collector box.
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—
8
38.
While unit is operating in low heat, jumper R and W2.
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—
39
39.
Do you have burner pulsations in high heat?
37
8
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