Flame sensor questions??

[martyinlincoln]

I installed a couple of those add on flame sensor kits for Rheem/Ruuds. Been a while but if I remember correctly the sensor wire tapped into the neutral wire on the HSI so it read at both locations. The next generation control board took the flame sensor straight to the board.

[millertime77]

ran into samething yesterday that through me off right in front of the customer. I make a call for heat and the HSI lights the burners for about 2 to 3 seconds then the gas valve drops out. So presume the flame sensor is dirty, but wanted to check its output, so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp readingon my meter fluctuated from I believe it was .1 to .2, but the thing that was wierd to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out. I cleaned the flame sensor up real good, only because my company doesnt have any stocked on my truck or I would have replaced it, and works fine now. That is the way I was taught to check them, and didnt know exactly what my reading was suppossed to be but it seemed low and I was pretty sure the flame sensor was the issue.

[pacnw]

ran into same thing yesterday that through me off right in front of the customer. I make a call for heat and the HSI lights the burners for about 2 to 3 seconds then the gas valve drops out. So presume the flame sensor is dirty, but wanted to check its output, so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp reading on my meter fluctuated from I believe it was .1 to .2, but the thing that was weird to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out. I cleaned the flame sensor up real good, only because my company doesn't have any stocked on my truck or I would have replaced it, and works fine now. That is the way I was taught to check them, and didn't know exactly what my reading was supposed to be but it seemed low and I was pretty sure the flame sensor was the issue.

what was your reading AFTER you cleaned it?

.1 or .2 does seem low. usually want at least 1.0 if not greater.

[millertime77]

It was over 1, if I remember correctly 1.2.

[craig1]

so I put my meter in series with the sensor and wire, which on this furnace goes directly to the board. The micro amp readingon my meter fluctuated from I believe it was .1 to .2, but the thing that was wierd to me was the burners stayed lit this time. So I hooked it back up with out the meter and gas valve drops out.

I just worked on a Carrier rooftop unit with this exact issue. It had an aftermarket board in it.


with everything connected normal it would not sense flame and shut down. As soon as I put my meter in series with the flame sensor, everything ran fine and I got a 5 microamp signal. I hooked back up without the meter and it would no longer sense flame. WTF?

I pulled the board from a neighboring unit and it worked fine in this unit. When I put the questionable board in the other unit it no longer worked at all. There must have been something wrong with the board so I am exchanging it. (only 5 months old, but has never run in heat mode)

[gravity]

check the voltages the board is outputting on the flame sensor.

had a 1 year old york sunline last week. burners not lighting.

check volts on flame sensor wire; had 0 volts.

condemned board.

same unit next to it was sending 115v thru flame sensor.

all boards are different though. they may send 70 volts, 30 volts, 115 volts......

another thing to check is molex plugs. if water gets in them they can cause erratic problems.

[doc havoc]

I just worked on a Carrier rooftop unit with this exact issue. It had an aftermarket board in it.


with everything connected normal it would not sense flame and shut down. As soon as I put my meter in series with the flame sensor, everything ran fine and I got a 5 microamp signal. I hooked back up without the meter and it would no longer sense flame. WTF?

I pulled the board from a neighboring unit and it worked fine in this unit. When I put the questionable board in the other unit it no longer worked at all. There must have been something wrong with the board so I am exchanging it. (only 5 months old, but has never run in heat mode)

Should have just left your meter in the circuit and charged the customer for a new meter.

[millertime77]

Should have just left your meter in the circuit and charged the customer for a new meter.

Why? Is that not how you are suppossed to check a flame sensor? Will it ruin the meter like that?

[martyinlincoln]

Don't forget to clean the burners and crossovers when you clean that flame sensor. There has to be a good path to ground and it doesn't take much rust to mess with 1 microamp.

[Joehvac25]

This is a good thread


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[hurtinhvac]

check the voltages the board is outputting on the flame sensor.

had a 1 year old york sunline last week. burners not lighting.

check volts on flame sensor wire; had 0 volts.

condemned board.

same unit next to it was sending 115v thru flame sensor.

all boards are different though. they may send 70 volts, 30 volts, 115 volts......

another thing to check is molex plugs. if water gets in them they can cause erratic problems.

X2

Though I've never seen anything as low as 30V.

Always remove molex and/or spade connectors to suspect components, reinsert, repeat, repeat and repeat. I don't completely understand how a clean looking plug or spade can be the culprit, but one in maybe 10 times it's just that quick and easy.

I sometimes wonder how many "bad" boards were actually just a corrupted connection that was "fixed" when the new connectios were made to the new board.

[Joehvac25]

X2

Though I've never seen anything as low as 30V.

Always remove molex and/or spade connectors to suspect components, reinsert, repeat, repeat and repeat. I don't completely understand how a clean looking plug or spade can be the culprit, but one in maybe 10 times it's just that quick and easy.

I sometimes wonder how many "bad" boards were actually just a corrupted connection that was "fixed" when the new connectios were made to the new board.

I heard somewhere that 40% of boards sent back were still ok. That number could be wrong because I heard awhile ago but since this is the Internet and you read it it automatically makes it true.


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[hurtinhvac]

I heard somewhere that 40% of boards sent back were still ok. That number could be wrong because I heard awhile ago but since this is the Internet and you read it it automatically makes it true.


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I believe it.