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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7791
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Goodman 100-4. Igniter lit no burner. Replaced

Customer Question

I have a Goodman 100-4. Igniter lit no burner. Replaced board and transformer. Ran ok for six hours. Now back to original issue
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: About two weeks since heat needed noticed ignition light but that’s all after one use. Replacing parts got it working fine again only for a few hours then back to only igniter going through 3 cycles and resetting. Just like before no 24v to valve
JA: Have you tried power cycling the appliance -- unplugging it and leaving it off for a few hours?
Customer: Yes
JA: Do you plan on doing the work yourself?
Customer: I have done all the troubleshooting and part replacement myself. Thought I had it fixed but back to original issue. I am about ready to give up and call pro tech.
JA: Anything else we should know to help you best?
Customer: It is about 13 years old and first problem. AC side works fine. Blew out burner tubes. Heat exchanger and new filter.
Submitted: 11 months ago.
Category: HVAC
Expert:  BillyHvac replied 11 months ago.

Hello,

Is this a GMP or GMPN?

Customer: replied 11 months ago.
GMPN
Customer: replied 11 months ago.
I did ohm test on rollout switches, tested pv switch and thermostat before replacing board and transformer. It then would fire up but cut off once the blower started up. According to the new board instructions it said if this occurred switch 24v leads. Once that was done it worked as expected for about 6 hours and a few on and off cycles. It then went back to the original problem. I swapped out the old board and no change. Could there be some reason the board would go bad or be fried that quickly?
Expert:  BillyHvac replied 11 months ago.

in the same series as the gas valve....meaning once power is sent to gas valve it must cross a couple "bridges"...

Do you know if your unit has an auxiliary limit? If you trace the 24v wire backwards from the gas valve does it go to a limit in the blower section?

Customer: replied 11 months ago.
The gas valve blue wire traces back to the 24v pigtail that includes the ground and into the board at pin #6 on the nine pin connector. I have jumped both the limit, pv and burner box switches at times during my initial system checks and all switches work. As I said earlier replacing the board and transformer got the system working so all paths thru the switches are good. It is after running it went back to the original status of three times trying to get burner to light then flashing one on the board. This is because there is no 24v trigger from the board to allow a voltage path to the gas valve to get initial ignition. I am sure that something has damaged the board or transformer as I have 120v ac into transformer but never see the 24v on the other side of the transformer, at the gas valve or at pins # 3 and 6 of the nine pin connector. If one of the switches was opening after a few cycles off heat on and off my jumping them should allow the system to run at least for awhile. Is there something that would take out the board after so short a time?
Expert:  BillyHvac replied 11 months ago.

If no 24 on 3 and 6 then the transformer is bad. This can be because of any short in the low voltage circuit.

A transformer can run hot with a partial short to ground, bad gas valve etc. After cooling down it can work until eventually burns out. Is there a fuse on the board (yellow 5 amp)?

Customer: replied 11 months ago.
There is a yellow 3 amp fuse but it is not blown. The transformer they sent me was a 120/240v ac where you pick the common and 120 or 240 voltage pin. It was hot to the touch when I went down to trouble shoot this morning. I will pickup a 120v only transformer tomorrow and see if that works. If it does is the a way to test load on the transformer while running or a way to see load on gas valve to detect a short? I maybe at the point of local help if a different transformer does not get me back up. I don't just want to replace t formers and boards a few more times.
Expert:  BillyHvac replied 11 months ago.

Some transformers you have to watch how they wire...especially multitap...we are trained to think black as power...but the transformers (some) use black as common...

If you get a multitap just watch how it is wired..