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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8067
Experience:  Furnace, A/C and heat pump specialist.
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Why does my Goodman furnace turn on and off?

Customer Question

My goodman furnace will turn on then almost immediately turn back off and will do this continuously. If I turn the t-stat off when it first turns on it will stay on longer. I am very confused as to what is going on here
Submitted: 5 years ago.
Category: HVAC
Expert:  airheatman replied 5 years ago.

Please provide a few more details. Do you mean when you turn thermostat to heat, everything comes on, then shuts right back down?

Customer: replied 5 years ago.

The t-stat is set to heat. The furnace will turn on and then immediately turn off and keep trying to turn on over and over. I can hear clicking from the board during this time as well. The light comes on, on the circuit board and goes out when the furnace turns off. On then off. On then off. What is weird is as soon as it kicks on, if I turn the t-stat to the off position it will stay on much longer. Then time out and turn off.

Expert:  airheatman replied 5 years ago.
Try this. Remove the R and W at thermostat and twist them together.Lets bypass the thermostat and see if furnace comes on and stays on just to eliminate it being a problem.
Customer: replied 5 years ago.
Alright I did this and there was no change. On and off....on and off
Expert:  airheatman replied 5 years ago.
OK, the inducer motor comes on ignitor comes on burners light, then go back out correct?
Customer: replied 5 years ago.
No, I do not know what an inducer motor is, but it never gets to the ignitor or burners. When I say it comes on, I mean its first initial burst of power. I am going to imagine this is the inducer motor. But it kicks on for less than 2 secs and turns right back off.
Expert:  airheatman replied 5 years ago.

Do you have a volt meter to check and see where we are losing power?

Customer: replied 5 years ago.

Yes. I have a volt meter. This is the frustrating part. I just turned it off at the t-stat so that it would not keep trying over and over, and it stayed on for almost 10 seconds longer.

Expert:  airheatman replied 5 years ago.
OK, lets start here. Remove the bottom panel from furnace.Tape door switch in.Locate the control board and on the control board find terminal L1 and a neutral where power comes to board,Turn on power, turn to heat,Check at L1 and neutral and verify the 120 volts is constant on L1 and Neutral.Then we move on
Customer: replied 5 years ago.

I cannot find the what you stated. I do have 120 steady coming into the 24v transformer. The meter jumped when I had it on hot and touched the side panel of the furnace. Is it possible I have a short somewhere?

Expert:  airheatman replied 5 years ago.

Check the high voltage connections where they wire nut to the furnace wires and make sure they are not loose

Customer: replied 5 years ago.
Okay I checked the main lines. the wire nuts were tight. I double checked and have steady 120 coming in, But when I checked for incoming voltage, with the hot connected I got a reading when I touched the ground to almost every part of the furnace.
Expert:  airheatman replied 5 years ago.

Ok it seems like all is good up to the control board.Are you getting a flash code from the LED on the board when you turn power on?

Customer: replied 5 years ago.

No, the light comes on as it powers up, then goes off with the whole unit. But no code of any sort. It was one of the first things I looked for.

Expert:  airheatman replied 5 years ago.

If the 120 is steady to the transformer and the 24 volts is steady from the transformer I am going to say you have a problem in the control board.However, this board runs a couple hundred bucks, so I would recommend having a tech verify before replacing the board