Natural Gas Furnace - no heat

Discussion in 'HVAC' started by madrussian, Dec 20, 2016.

  1. Dec 20, 2016 #1

    madrussian

    madrussian

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    Got an Amana/Goodman natural gas furnace. Model CHPF1824A6AA, about 12 years old.

    Has worked great until late last week. LED lights blink 3 times, indicating an induction air problem.

    I checked the vacuum switch - infinite resistance when induction fan is off. When induction fan turns on goes to zero resistance. I think this is OK.

    Checked limit switch, it being cold - is closed at zero resistance (not open) - i think this is OK.

    I need to check the . But what else do I need to check?
     
  2. Dec 20, 2016 #2

    madrussian

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    I also tested the ignition element - giving me 50 ohms - so i am assuming this is OK?
     
  3. Dec 20, 2016 #3

    Snoonyb

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    The #CHPF1824A6AA, is for the "A" coil, not the furnace.
     
  4. Dec 20, 2016 #4

    buffalo

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    Does it fire at all? Check and make sure your exhaust and intake pipes are not blocked either by snow or pests .
     
  5. Dec 20, 2016 #5

    madrussian

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    Nope does not fire. The induction fan turns on, vacuum switch closes, but nothing after that. Vacuum switch seems to operate properly but the thing does not fire up.
     
  6. Dec 20, 2016 #6

    madrussian

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    anyone know the order of operation? Should burner kick in next, then main blower turn on?

    I am thinking main control board...
     
  7. Dec 20, 2016 #7

    kok328

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    what's your voltage on the HSI after the vacuum/pressure switch closes?
     
  8. Dec 20, 2016 #8

    madrussian

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    HSI is the igniter? Should I unplug the igniter and measure voltage across those two leads?
     
  9. Dec 20, 2016 #9

    nealtw

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    You didn't answer all of Buffalo's question.

    page_Snow_Furnace_Intake_2.jpeg
     
  10. Dec 21, 2016 #10

    kok328

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    Your trying to determine voltage TO the inginiter so test the leads that connect to the igniter, not the leads on the igniter.
    and of course you know not to touch the igniter with your fingers.
    Inspect the igniter for hot spots and hairline cracks but, i think you already ohmed it out at 50
     
    Last edited: Dec 21, 2016
  11. Dec 21, 2016 #11

    madrussian

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    Sorry - yeah replaced all filters. Didnt climb on the roof (not a ladder guy). However given the information that when induction fan comes on, the pressure switch closes, I think it is safe to assume there is no blockage on top of the roof.
     
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  12. Dec 21, 2016 #12

    madrussian

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    Sorry yeah that is what i meant - voltage to the igniter. I checked this and I now think the power supply is suspect. got 120 VAC going to the PS, but nothing coming out of the 24 V.
     
  13. Dec 21, 2016 #13

    kok328

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    If your transformer was bad you would not have gotten that far in the ignition sequence.
     
  14. Dec 21, 2016 #14

    DFBonnett

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    FWIW, some years back I had the same problem, but on a less complicated furnace. The gas valve had failed and did not open. A new gas valve was the fix.
     
  15. Dec 22, 2016 #15

    WyrTwister

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    Can you visually verify if the HSI comes on or not ?

    Can you post a photo of the control wiring diagram ?

    Pretty sure the HSI operates on 120 VAC .

    God bless
    Wyr
     
  16. Dec 22, 2016 #16

    madrussian

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    I assume the HSI should come on after the induction fan comes on:

    Yes after looking at the schematic in the manual, the HSI is on the high voltage (120v) circuit.

    I need to look at this a little closer. Should be able to check this voltage today - got a multimeter that works.
     
    Last edited: Dec 22, 2016
  17. Dec 22, 2016 #17

    kok328

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    Your jumping all over.
    Use a systematic approach to troubleshooting.
    Start with line power and then check control power.
     
  18. Dec 22, 2016 #18

    madrussian

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    Agreed.

    Part of what I do not know is order of operation of a furnace. No Idea. If anyone can provide this, would be a great help!

    Part of my initial problem was the multi-meter I have was suspect, so some of the first troubleshooting was not accurate.

    This is what I know/done:
    1. First noticed an issue. Induction fan would run, nothing else.
    2. The LED was flashing 3x. According to manual this is a vacuum switch/induction problem.
    3. Replaced vacuum switch, no change.
    4. Checked resistance of both switches. Both are OK. When induction fan OFF = infinite ohms. When induction fan ON = 0 ohms.
    5. Checked resistance of HSI = 53.9 ohms.
    6. Double checked all incoming voltages (with new multi-meter). Got 120 VAC at main on/off switch, junction box going into furnace and at the transformer.
    7. Checked voltage going into the HSI. Getting ~1 VAC. But again I do not know the order of operation. So I do not know if this should be ON or OFF yet.
     
  19. Dec 22, 2016 #19

    madrussian

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    Checked voltage coming off the control board to HSI - nothing there. (with induction fan ON)

    Also checked primary limit and aux limit switched - both are closed (indicated normally closed on schematic).

    When I was checking voltage on the control board a few of the relays were turning on/off, so possibly the control board has failed?
     
  20. Dec 22, 2016 #20

    madrussian

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