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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8429
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have the exact same symptom as this person, Just today, my

Customer Question

I have the exact same symptom as this person
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: Just today, my tenant let me know her heater was not working properly
JA: Do you plan on doing the work yourself?
Customer: If it is simple enough. I have been doing a lot of troubleshooting to try to figure this out.
JA: Anything else we should know to help you best?
Customer: I dont know?
Submitted: 6 months ago.
Category: HVAC
Expert:  Rick replied 6 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

What's the brand and model nmber of your unit?

Customer: replied 6 months ago.
I have a goodman GMNT 040. It clicks on, the blower spins for a sec, then it clicks off. Sometimes very rapidly, and sometimes the furnace will run for a few minutes.Here's what I have already attempted:I cleaned the flame sensor with 1000 grit sandpaper.
I checked the 110 into the blower, the blower gets 110 when it clicks on, and does not when it clicks off.
I have cleaned all of the spade connectors with electrical contact cleaner and ensured they are all seated properly.
My thermostat is a nest, and I verified that the thermostat is not the problem by connecting the signal wires at the furnace
I can't find the fan limit control to test it, but because this happens without the furnace heating up I don't think that is the problem.
I'd like to check the fan relay but I don't know where to find it.
Expert:  Rick replied 6 months ago.

I'm going to open this up to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Expert:  Phil replied 6 months ago.

Hello, there are two blowers on that furnace, the main blower that is grey and 14" ciube size, and the much smaller inducer fan, generally black and with a small 4" diameter motor attached.

I need to know very specifically which blower you are referring to.

How long has the NEST been installed?

If the main blower comes on before the furnace heats up, and if there is now blower control on the wiring diagram, then the blower is controlled by a timer built into the printed circuit board.

The fan relay is most likely ON the printed circuit board, its small about 1/2" tall and 1" x 1/2" two wires from the main blower motor will attach directly the printed circuit board in that case.

We can do a heat stress test on the printed circuit board. Use a hair drier to slowly and gently warm the PCB to 125F... if it is defective due to internal micro cracks, those will expand and make the problem worse, or make the problem dissapear all together.

In either case the PCB is bad and needs to be replaced

We can go from there as needed.

Customer: replied 6 months ago.
I am referring to the inducer blower.I installed the nest several years ago when it first came out.It seems you are right about the pcb being bad.
Expert:  Phil replied 6 months ago.

Did you do the heat stress test on the PCB? what were the results

Expert:  Phil replied 6 months ago.

I will be gone to the dentist in half an hour, then will return here to follow up with your response after I return, I am in until 10 pm west coast time

Customer: replied 6 months ago.
I just completed the test. I used my wife's hair dryer and an infrared thermometer to check the temp. I have taped the door switch to allow operation when the door is open. The room is cold, so the starting tempo of the board was around 60F. The unit was clicking every few seconds, and as it started to heat up the clicking increased. by 105f the clicking had gone to several times a second and I stopped the test.
Expert:  Phil replied 6 months ago.

Thanks. that result proves that the board is bad to the 98%+ level

Please rate my work, I will appreciate it and will hold the question open to you for any follow up that you might need later.

Customer: replied 6 months ago.
Do you know where I can get one?
Expert:  Phil replied 6 months ago.

Yes, you can get one on line from

Here is the direct link again, its blue, click on it

ShortysHVAC is a wholesaler of all parts and components in a Heating or air conditioning system including those heater kits.

Let me know if you have any trouble at all clicking on the link, or getting ahold of them. When you get to their web site, call them on the phone, do not bother trying to navigate the site yourself.

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