Flame sensor is good

[Ac_man]

I was on a service call today, 80% upflow goodman furnace natural gas. Burners would light up for 5-10 sec, then cut off. I cleaned flame sensor with sand paper,still same results. Microamps were 2.2. Can it be the circuit board not taking in the proper signal from flame sensor

[kangaroogod]

Sure,,, or it could be something else.

[Ac_man]

Like what

[BMH_SE]

Not enough info, flame sensor description isn't enough for us to know what going on with the unit.

[socotech]

Be sure you have a good ground. BTW, sandpaper is not recommended for cleaning flame rod (I have done it too). I try to use steel wool as this doesn't possibly insulate flame rod. One time I had to replace control board that wouldn't see flame signal.

[Ac_man]

Where should i check the ground

[Core_d]

Where should i check the ground

i would like to know this too

[Ac_man]

I did check for gas pressure and was 3.5"wc. Next i removed all burners and cleaned them out. After all this, still had same symptoms. What should i do next guys

[hvacnut]

Be sure to check the air intake and vent pipes for partial blockage. Also, the reason not to use sand paper is that small particles of sand will get embedded in the sensor and then the flame will cause them to turn to glass and insulate the sensor. I use a 3M scouring pad like you use to clean dishes. This works as well as steel wool but you can actually keep it in your pocket.

[Mr Bill]

Where should i check the ground

I would start by checking from your "neutrals" on the board to any place on the chassis that is a good ground, make sure the unit is calling for heat. Also read it from the flame sensor to chassis and then to neutral on board, again make sure the unit is calling for heat. your going to read a .03 volts, maybe a little more or less, anymore you have a grounding issue.

[Ac_man]

I would start by checking from your "neutrals" on the board to any place on the chassis that is a good ground, make sure the unit is calling for heat. Also read it from the flame sensor to chassis and then to neutral on board, again make sure the unit is calling for heat. your going to read a couple volts, anymore you have a grounding issue.

Would i have to disconnect any neutral wires or just test to a OPEn neutral terminal?

[Mr Bill]

Would i have to disconnect any neutral wires or just test to a OPEn neutral terminal?

I had to go back and edit the volts don't know what I was thinking, No just read from the way I listed it, you don't have to to disconnect anything. I had a 1993 Ruud unit last week that I discovered a bad ground on from the flame sensor to the board, it was acting the same as your unit. Most of the time I find it's a bad sensor or board, and I was just about to condemn the board when I discovered a bad ground. The ground wire from the sensor to the molex plug was loose, I have a tool to take out the pins in the molex plugs, and I just installed a new pin and it was good to go.

[Core_d]

I would start by checking from your "neutrals" on the board to any place on the chassis that is a good ground, make sure the unit is calling for heat. Also read it from the flame sensor to chassis and then to neutral on board, again make sure the unit is calling for heat. your going to read a .03 volts, maybe a little more or less, anymore you have a grounding issue.

Thank you mister bill. I like that answer im gonna mess around with this next lab day at scool loosen wires and what not