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    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #1

    Mar 10, 2008, 05:54 AM
    Crazy voltage at 2 stage gas valve
    I have a 3 month old 2 stage goodman gas furnace that is making a clicking sound at the gas valve. What happens is when the themastat calls for heat the draft motor turns on and that's when the clicking sound begins at the gas valve. I took a voltage reading at the gas valve during this clicking and at h connector I'm getting anywere from 15 volts to 28 volts. The at the m connector I do not get my 24 volts until the hot element lights up . The furnace always starts but the clicking is driving me crazy. I replaced the gas valve and that did nothing. I'm thinking of replacing the control board next but I'm not sure if that will fix it or not
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #2

    Mar 10, 2008, 08:15 AM
    Check all your ground connections from the inside of the furnace to the furnace disconnect and then to the main electric panel for starters. I have seen more problems due to bad grounds since most of the new style (circuit board) furnaces arrived years ago. The newer models seem to be even more suspect when it comes to grounding.

    Has this been going on since you installed it?

    Are you running a two stage thermostat?
    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #3

    Mar 10, 2008, 08:32 AM
    The ground is good the problem starteded a month after install . I am using a 2 stage thermastat
    tsa7man's Avatar
    tsa7man Posts: 154, Reputation: 9
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    #4

    Mar 11, 2008, 07:14 AM
    The clicking is most likely the pressure switch, causing the gas valve to cycle the solenoid. A quick check is to take a jumper wire behind behind the two wires on the pressure switch ( just pull off the two wires enough to get behind them) as the inducer starts to run ( about 4 seconds after it starts) NOTE: this is a safety device, only jumper to test for a problem. If this corrects the clicking, the problem is in the venting and or inducer, usually water ( condensation ) backing up in the unit,. but could be a venting issue as well.Post back your findings...
    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #5

    Mar 12, 2008, 06:14 PM
    OK by jumping the 2 wires on the high fire pressure switch this cured the problem with the noise coming from the gas valve. The voltage is no longer jumping around either. With the jumper in place the pressure switch is still clicking a lot. How can I troubleshoot the pressure switch? The venting seems fine so what else can I do?
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #6

    Mar 12, 2008, 06:38 PM
    ((how can I troubleshoot the pressure switch))

    You did your troubleshooting when you jumper it switch and the unit stopped making the noise.

    Now you might want to check the tube that is connected to the pressure switch for any obstruction or take a gauge and test for vac/pressure of the furnace then check the factory set point stamped on the switch.

    You never mentioned the model number of your unit. We are pretty good on this board but not mind readers.

    One last thought. If you are using a two stage thermostat are you sure the second stage is not trying to kick in? Disconnect the second stage wire so as to not feed the circuit at all and see if the problem also goes away.
    juggallojed's Avatar
    juggallojed Posts: 165, Reputation: 10
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    #7

    Mar 12, 2008, 06:45 PM
    Quote Originally Posted by tim1275
    ok by jumping the 2 wires on the high fire pressure switch this cured the problem with the noise coming from the gas valve. the voltage is no longer jumping around either. with the jumper in place the pressure switch is still clicking alot. how can i troubleshoot the pressure switch? the venting seems fine so what else can i do?

    Sometimes water (condensation) collects in the tube to the pressure switch.

    Look for a restricted tube to the pressure switch or a blockage in the flue.

    Any downward looping of the tube will create a trap for the water,
    Try to re route the tube to remove the low spot.
    tsa7man's Avatar
    tsa7man Posts: 154, Reputation: 9
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    #8

    Mar 12, 2008, 07:45 PM
    As hvac1000 posted, he gave you a number of things to look for... and here is my two points. Follow the hose from the pressure switch, pull it off that end connecton ( not at the pressure switch) and see if you have any water flowing out of that connection?. with the furnace powered off... Since you have a 90% furnace.. the problem is most likely the back-up of the condensation water in the unit and not draining... kindly post the model number and make of your furnace...
    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #9

    Mar 13, 2008, 06:54 AM
    OK by jumping the 2 wires on the high fire pressure switch this cured the problem with the noise coming from the gas valve. The voltage is no longer jumping around either. With the jumper in place the pressure switch is still clicking a lot , can a pressure switch go bad how can I troubleshoot the pressure switch the venting seems fine
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #10

    Mar 13, 2008, 07:05 AM
    Kindly post the model number and make of your furnace...
    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #11

    Mar 13, 2008, 04:54 PM
    The furnace is a goodman gmv950905dxa
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #12

    Mar 13, 2008, 04:59 PM
    Clear vent tube of all obstructions
    If that does not work replace pressure switch.
    tim1275's Avatar
    tim1275 Posts: 6, Reputation: 1
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    #13

    Mar 19, 2008, 03:40 PM
    The problem was the pressure switch. Thank you very much for helping me out and saving me money . I was about to buy a control board before I gained some knowledge from your help
    Thank again
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #14

    Mar 19, 2008, 04:29 PM
    No problem. Glad you got it fixed.
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