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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8369
Experience:  Furnace, A/C and heat pump specialist.
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I have a GMPN)60-3 Goodman furnace that I am troubleshooting

Customer Question

Hi, I have a GMPN)60-3 Goodman furnace that I am troubleshooting and the gas valve wont turn on.
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.

Does the small vent motor where vent leaves furnace come on and stay on?

Customer: replied 2 years ago.
It turns on right away, then cycles off for a second and then comes back on. After the second cycle, the man fan motor turns on as well while the ignitor is on. I never hear the gas valve cycle. When I measure it I only get 8 volts there but that is always there as soon as I turn the breaker on for the furnace. I checked the sensors around the heat exchangers where the wire leads to the gas valve and I get no resistance through all of them. I went outside and felt the air coming out and its got good flow,
Customer: replied 2 years ago.
I just tried it again. The vent motor turns on right away and runs for 4 or 5 seconds and then turns off for 2 seconds and then starts up again along with the main motor.
Expert:  airheatman replied 2 years ago.

Try this. Remove the rubber hose from inducer and leave it attached to pressure switch. Allow inducer to start, then suck on hose until you hear pressure switch click.Keep a vaccum sucked on hose and see if burners will ignite.

Customer: replied 2 years ago.
I tried that already with no change. I will try again though. I do hear the click when I do that.
Customer: replied 2 years ago.
Just tried it a few more times. WHen it first starts and I start sucking on it, if I keep sucking on it when the vent motor turns off, it won't try to start again. When I suck on the hose when the motor starts up and stop sucking on it when the motor stops, it will restart and the ignitor will keep on. Still no gas turning on.
Expert:  airheatman replied 2 years ago.

Ok that inducer should not be starting and stopping.Once thermostat comes on, the inducer should run nonstop until thermostat is satisfied. Do you have a meter to see if we have 120v constant to inducer?

Customer: replied 2 years ago.
When you say inducer you mean the ventor motor? I have a meter and will put it on now.
Expert:  airheatman replied 2 years ago.

Yes that is the motor you are saying is going on and off correct?

Customer: replied 2 years ago.
When you turn the furnace on, it turns on and then the pressure switch connects, then it turns off and the pressure switch disconnects and then it starts but never turns off again. I think it is checking if the pressure switch is bypassed because when I do jump the switch, it won't restart again. Once it does the system check (about 4 seconds in), it run and never stops running.
Expert:  airheatman replied 2 years ago.

The vent motor is what controls the pressure switch.It should never shut off during heat cycle.The inducer(Vent motor) pulls a vacuum on the pressure swicth and has to stay running or we lose vacuum and pressure switch opens which shuts down burner process.

Customer: replied 2 years ago.
I measured the voltage and it gets 120 volts from the motherboard. I will check again to see if it turns off and back on like the motor is.
Expert:  airheatman replied 2 years ago.

See if motor is stopping with 120v still present to motor

Customer: replied 2 years ago.
I just checked it again. The motherboard is turning off the voltage. I hear the relay click in the same timing as with the motor connected.I think they do that the first time you turn on the furnace to check the pressure switch as it does it once and then keeps the fan on and ignitor going. What is surprising is that it keeps it going even though there is no flame. You would think it would give up when the flame rod isn't detecting anything.I think the motherboard might be goofy. I checked the resistance across the gas valve and it was 0.
Expert:  airheatman replied 2 years ago.

I am suspecting board is bad,

Here is how it works:

On call for heat board checks to make sure pressure switch is "open".If not nothing else will happen and board will give an error indicating PS closed.

If pressure switch is open, board sends 120v to inducer.

Inducer pulls a vacuum on switch closing it.

Once board senses pressure switch is closed, it signals igniter. Once igniter is hot or sparks, depending type, board sends 24v to gas valve and it opens allowing burners to light. Then the flame sensor verifies flame lit and allows burners to keep burning and energizes main blower.

If any of those components fail to do there job, burners shut down, inducer and blower keep running and we get an error code..

But at no time during the cycle should inducer ever stop until thermostat has satisfied.

Customer: replied 2 years ago.
I checked the voltage to the gas valve and it is always 9 volts. Weird. I will buy a new board tomorrow and see if that fixes it.
Expert:  airheatman replied 2 years ago.

PLease follow up and let me know .

Customer: replied 2 years ago.
Hi,I have ordered the part and once it arrives - I will let you know if it works. I wasn't able to find it locally.Thanks,Jeremiah
Customer: replied 2 years ago.
The part comes in on Thursday and I hope to get it installed on Friady. Will let you know.