American Standard furnace not firing.


  #1  
Old 12-03-15, 12:59 PM
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American Standard furnace not firing.

Hi guys,

Furnace is an American Standard mod# aud080c936j0

Problem: Furnace diagnostic light flashes fast (asking for heat).
Inducer comes on.
igniter does not come on.
Furnace repeats sequence 3 times and then enters lock out mode.

What I tested when the unit was calling for heat:
I have 28 volts to both terminals of both limit switches.
I have 28 volts to all 3 terminals of the pressure switch.
Tested continuity of the igniter and it was good.

I am thinking the board is bad. Am I missing something else I should check? Does the igniter have to fall under a certain resistance to function? (I only tested continuity). Thanks for the help.
 
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Old 12-03-15, 01:57 PM
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Are the LEDs flashing a code when it locks out?
 
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Old 12-03-15, 02:13 PM
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No, just the lock out code.
 
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Old 12-03-15, 03:14 PM
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Take the cover off and there should be a list of codes that will tell what's wrong. Let us know what you find.
 
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Old 12-03-15, 05:21 PM
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After the pressure switch closes, the next thing that should happen is for the circuit board to turn on the power to the hot surface ignitor.

You should measure the voltage being applied to the ignitor, which is commonly 120 VAC. Presumably you are getting no voltage there, but I'd double check that to be sure.

If you aren't getting that voltage, the circuit board is defective since it's not switch on that voltage.

However, typically the circuit board would turn on the main burner gas for 2-3 seconds before shutting it off since the gas isn't lighting. Is that happening?
 
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Old 12-03-15, 05:21 PM
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Welcome to the forums.

No, just the lock out code.
What is THAT code ?

These furnaces are hard to find exact service info for.
Is this a single or two stages furnace ?
Do you see two pressure switches ?

Your problem is a classic pressure switch not closing issue. You said all three terminals showed 24vac ? When the draft inducer is not running there should be no power on one wire. When the inducer starts to run.... then there is power on that terminal.
 
 

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