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American Standard Gas furnace acting weird

I am a heating tech and i am just confussed. Well i think its the board but just looking for a second opinion. Call for heat and the ventor motor starts. after a few seconds the ventor quits and the main blower starts and the fault code states it is reverse wiring, something to do with the ignitor or low voltage. The power comming from the board to the ventor is 120 to ground and 168 volts to neutral. I also have a an amp draw of 10amps at the ventor but if i check the amps at the line wire coming into the furnace i only draw about 1 amp which is normal. I am pretty sure it is the board but i am not used to the american standard furnaces. It is a new american standard stage with reg motor. The main power coming in is good and polarity is good and properly grounded as far as i can see.

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  • subzero_hc Jan 21, 2009

    Ya i have checked the polarity and the grounding and they are both good. Doyou think it is posible for the relay for the ventor to have a high resistance through it causing the high amps? but you would think that you would get high amperage at the main power coming in the unit. The fault code does say that oe posibility is that ignitor, but the ventor doesn't even run long enough to go through the sequence of operations. I wonder if the board does some sort of resistance chech on the ignitor as it is calling for heat. I checked the resistance on the ignitor the other day and it was low and didn't seem too high though. But then everything falls back on that weird voltage to the ventor. I cant even find a number to call American Standard. Let me know if you have any questins or ideas...

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I am concerned of the readings you have given. 120 volts to ground, but 168 volts to neutral? And having 10 amps of current at the "ventor", but only 1 amp for the whole furnace worries me, because power for the "ventor" comes through the furnace.

You should not have 168 volts to anything! Unless somehow 240 volts is feeding the system, and there is a medium resistance short somewhere.

The controller boards are sensitive to AC polarity (if you will). Neutral should be tied to neutral on the board. You can check that by testing for voltage between the neutral terminal and chassis ground (assuming the chassis is properly grounded.). The hot leg of incoming power, which should be 120 volts, should be connected to the terminal that says 120 VAC.

If your getting 168 volts AC somehow, then something is wrong, and you need to disconnect power from this unit until you find the cause.

As a heat-A/C tech, you should know the sequence of operation for all furnaces is pretty much the same. The boards, while manufactured by different manufacturers, all operate pretty much the same way.

Let me know your findings in reply and I will attempt to help you more.

Posted on Jan 20, 2009

  • Mark Egan Jan 21, 2009

    Assuming the "ventor" motor you are talking about is the combustion air fan, if it's power source is the controller board, then the current pulled by the combustion fan should be seen on the power in-feed side to the furnace, and board.
    If it doesn't (and what you describe doesn't), then your looking at an incorrectly wired system. You should be seeing wires that have been cut and spliced that were not factory cut and spliced.

    The relay will not "create" current with a high resistance of some type. You need to go back and remember ohms law to know that (when considering the above as well.), as well as visualize the internal workings of the relay. You whould be able to measure any perceived high resistance that your thinking.

    When you measured the "ventor" motor current, were you measuring the incoming power current at exactly the same time, in order to know the "ventor" was pulling 10 amps while the incoming power was 1 amp?

    Does the ventor motor run?

    I have had a piece of trash (LPS) get in the rubber tube connected to the combustion air "fan prove" switch shut a system down before. Don't remember the code we got, but, the code gave no indication that the combustion air switch was having a problem. And the LPS was hard to identify as it was lose inside the combustion fan housing.

    American Standard is the old Trane. www.americanstandair.com .

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