Furnace is all blow / no heat. - FIXED!

[dras]

OK gang, I've been searching high and low and still haven't found the one piece of informatio I need. Like several others in the past, I have a problem where my furnace blows, but will not ignite. This is on a '97 Jayco with Atwood 79 series DSI type furnace. It seems like everything is working as it should, but I can't get it to ignite. This all started one night last spring on a chilly night in the mountains. Furnace was working fine when I went to bed, but midway through the night I noticed it was only blowing and not firing. Decided I'd finally have a look at it today before the weather cools off again up in the high country. Stove & water heater both work fine. Here's what I've done / observed:

1) I jumpered out my thermostat to force it on (it's still 100 degrees here in Phoenix today & thermostat won't go that high). Voltage seems to be getting to where it needs to be. Through the overtemp switch, through the sail switch, and onto the DSI board.

2) Blower comes on like normal for a few seconds and then I can hear the gas valves open up with a solid 'click'. About 5 seconds later they close. They open up again a few seconds later, then close again in about 5 seconds or so. This happens 3 times as the manual indicates it should, but no ignition occurs.

3) I removed the burner assy. and electrode to inspect them and found them to be very clean and in good shape. Spark gap on the electrode is right at 1/8". I rigged it up so I could see the spark on the electrode outside the burner box, and I get 1 single spark at exactly the same time as the gas valves open each time.

4) Verified gas valves are opening by gently blowing through them and putting 12V on the coils. They open very firmly and I get good flow through them.

5) Switched to the other full propane tank (dual tank setup w/ automatic switchover regulator), but that didn't help. Have also tried it using both battery and shore power - same result.

6) Disconnected the propane line at the furnace and underneath the camper, and blew the line out with compressed air.

The question I have after all of this is about the spark ignition. As I stated above, I only get 1 single spark at exactly the same time the gas valves open. It would seem to be much more effective if it sparked several times 'after' opening the gas valve. I don't think the gas can even get from the valve, through the burner, and to the elctrode that fast. Is it supposed to do just one spark, or should there be several in rapid succession? Any help would be appreciated, this is very perplexing.

Thanks for helping,
Dave

[coach]

Atwood furnace trouble shooting

Mine sparks mutiple times. I'm guessing 3-5 before the woooosh of ignition!

Seems like you've tried everthing!

From the Troubleshooting 'BLOWER RUNS BUT FAILS TO IGNITE', there are several 'defective' possiblilities!

[PattieAM]

Your furnace requires 10.5-13.5 volts DC (battery) in order for the blower to open the sail switch and ignite.  If your battery is lower, the blower may run, but nothing else will happen.  Don't forget you have a 24/7 draw with your propane leak detector.

[Jim K in PA]

The question I have after all of this is about the spark ignition. As I stated above, I only get 1 single spark at exactly the same time the gas valves open. It would seem to be much more effective if it sparked several times 'after' opening the gas valve. I don't think the gas can even get from the valve, through the burner, and to the elctrode that fast. Is it supposed to do just one spark, or should there be several in rapid succession? Any help would be appreciated, this is very perplexing.

Thanks for helping,
Dave

Dave - I think you have isolated the problem.  It should spark multiple times, not just once.  It sounds like a problem with the ingniter control failing after the first discharge.  Look to that end of the circuit.  Perhaps replace the igniter circuit board.

Excellent trouble shooting regimen, BTW.  

[dras]

Well thanks Jim, it's what I do for a living. I'm an equipment engineer and work on semiconductor equipment. I'm pretty sure I need to coax more sparks out of it, but it seems like a failed board is the most likely culprit. Especially since it was working fine one minute, and dead the next. Don't see any burned components or cold solder joints on the board, so probably a weak capacitor or something. I just wanted to get a sanity check before plunking down $120 or so for a new circuit board.

Thanks to all, and happy camping!
Dave

[dras]

OK, for those of you that want to know (and I'm sure you're all on the edge of your seats!), I got this fixed today. It was indeed a faulty DSI ignitor board. Got a new one off eBay and stuck it in today. Fired up the first try! I could hear it sparking away like crazy several times a second, and after about 2 seconds it fired and worked like normal. Just for the record.

Thanks for the inputs.
Dave

[austinado16]

OK, for those of you that want to know (and I'm sure you're all on the edge of your seats!), I got this fixed today. It was indeed a faulty DSI ignitor board. Got a new one off eBay and stuck it in today. Fired up the first try! I could hear it sparking away like crazy several times a second, and after about 2 seconds it fired and worked like normal. Just for the record.

Thanks for the inputs.
Dave

Hey, nice fix and thanks for posting an update.  I wonder if it would be worth resoldering the connections on the back side of your old board and trying it again.

[Jim K in PA]

OK, for those of you that want to know (and I'm sure you're all on the edge of your seats!), I got this fixed today. It was indeed a faulty DSI ignitor board. Got a new one off eBay and stuck it in today. Fired up the first try! I could hear it sparking away like crazy several times a second, and after about 2 seconds it fired and worked like normal. Just for the record.

Thanks for the inputs.
Dave

Congrats Dave.  It sure sounded like you had isolated the problem.  Good result.

Now go camping!