Amana HSI no 24V to Gas Valve


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Old 12-04-11, 12:00 PM
R
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Amana HSI no 24V to Gas Valve

I'm looking at a AMS80703ANA HSI furnace that sends no 24V to the gas valve.

All safeties (roll-outs, pressure/vac switch, etc.) are operational and the main logic sends no codes until an ignition cycle is repeatedly attempted, then lockout code is displayed.

While diagnosing, I found that no 24V signal is sent to the gas valve. This reading taken at the control board itself.

The igniter functions at the correct time. I verified that the gas valve is operational by manually applying 24V to it momentarily.

An odd reading (I think) is the presence of nearly 65V to the flame sensor. Shouldn't the sensor be sending mV signal TO the control board?

My suspect component is the control board although most logic functions seem correct (ie. bypassing pressure switch produces give correct code), but I thought I throw this out there for any input before ordering this part.

Thanks in advance
 
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Old 12-04-11, 12:32 PM
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Yep, replace the circuit board.

An AC voltage is applied to the flame sensor. When the sensor is engulfed by flame, the flame rectifies the voltage and allows a small DC current to flow to chassis ground through the flame. Absent a flame, you have only the voltage present.

Sounds like you did an excellent job of diagnosing the problem.
 
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Old 12-04-11, 04:07 PM
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Thanks for the Kudos & you explanation of the Flame sensor.

R.
 
 

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