Ignition Problem Fix for Armstrong Ultra SX-80 Furnace

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A friend of mine just spent $100 having her Armstrong Ultra SX-80 furnace fixed. According to the repairman, this is a common problem with this model and is easily fixed by the homeowner -- so I thought I'd post the fix here and, hopefully, save some future reader a few bucks.
Her problem was that the furnace would not light. This unit has an electronic ignition that will not function unless conditions are OK in the combustion area. When the thermostat calls for heat, the combustion fan motor turns on, drawing in fresh outside air. The pressure caused by the fan is detected by a separately mounted pressure switch. If the switch is not activated, no ignition.
The pressure switch is connected to the combustion area by an 18 inch length of 1/4 inch rubber hose. It turns out that there is a lot of condensation in the combustion chamber in the area of the hose fitting and particles of rust can clog that fitting. Once the serviceman realized the pressure switch wasn't activating, the first thing he did was pull the hose off the fitting near the fan and ran a wire down the fitting bore to clean it. He reattached the hose, hit the power switch and the furnace fired right up. Total time: 10 minutes, tops.
I now know what to do next time -- and I expect there will be a next time.
Hopefully, I've saved you a service call.
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As I have already told you, he fix a symptom not the problem.
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kjpro
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Why is that? Would not a lack of vacuum to the pressure switch not allow the furmace to light? Tony D.

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On Sat, 14 Feb 2004 19:34:45 -0500, "CBhvac"

If the inducer was rigged to run all the time, how did the furnace continue to operate after the first cycle in which the pressure switch failed to open?
George
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Ignore the posting name, changed it for a sec in alt.hvac and havent bothered to change it back.
Simple...it was rigged on a standard peanut relay...When W was hot, it started the inducer. I might...and thats might, have some pics of that one around...if I do, you can see what a mess it was. He had a couple of old TI sequencers in there as well, that didnt belong.

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On Sat, 14 Feb 2004 20:22:19 -0500, "StephenM"

Why did he go through all that trouble instead of just letting the control board do its job? Or was the exchanger plugged to the point the pressure switch didn't prove, so he basically hardwired the inducer and used a relay in place of the pressure switch that would make and break on W in order to fool the computer? Now that would be Sweeet!!
Oh and if you're reading this, Stormin'...please don't get any ideas!
George
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Yup...exactly. I had a similar problem child not too long ago..an older Armstrong. I got this call about a unit that the other tech had said he "cant get that computer control anymore" and wondered if I could look at it. It worked sometimes, and most times not. It was a mess, in a crawlspace, and the vent was rusted, doors off, blower door switch hardwired, blower overheat limit hardwired, an extra relay or 4 in there..a bad HSI, and the best part was, once I got the HSI working, I had to prove what else was wrong, and start over. So..first things first, I get the thing to fire, and lo and behold, it does...problem is that the inducer and the blower came on at the same time. Turn the AC on....inducer was on..go freaking figure. Long story short...after ripping it down to nothing but the HSI control still in place, and starting over, there was nothing wrong with it other than some really, really reeeeeealy dumb wiring done by a tech from another company, that didnt have a clue. Funny part was, it was proof positive that if the fan starts at the same time as the inducer, the heat exchanger will never get to temp....the sounds of commotion from the owner when she thought the house was on fire..LOL..from the crap burning off the HE was priceless. Point is, you and I both know that too many people think an extra relay to make things work fixes the problem...

I thought of him...I really honestly did... I have even thought of printing up a sign, and when I run into a REALLY hacked one like that, taping it to it and snapping a pic for the website..:) Sign might say...SM was here....or...Stormy...is this your work?

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So IOW there should not have been a lot of condensation in the combustion chamber in the area of the hose fitting,causeing the rust in the first place? Tony D.
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On Sat, 14 Feb 2004 19:17:14 -0500, "Anthony Diodati"

Piss poor design. Look at the inducer housing. Is it covered with flaking black paint? Guess what...the inside is painted too! The paint flakes off and plugs up the port. Just popping a wire through the port will fix the problem but odds are it will come back shortly. The replacement inducer assemblies are no longer painted.
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Good to Know! Tony Dd.

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i get the same thieg when the coons nest - no fere
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