Original message
| hivoltage98
 |  "american standard no heat"
, posted Wed 25 May 23:11  
I have a american standard 90afue 2-stage furnace with variable speed blower that just doesnt wanna start heat? the t-stat calls for heat, it will cycle and ... nothing.. it will go through the 3 cycles until it still does nothing. the ignitor heats up, induction fan runs up, pressure switch closes, opens the gas valve and nothing. we had the tech out and he went through the standard steps, and we had low pressure from our propane tank. so we adjusted it and still wouldnt work. then he replaced the ignitor on a whim which still didnt work. then he replaced the white rodgers board and said that the board learns the firing time of the furnace so that it can save the ignitor. every time it fires it reduces the ignition time until it doesnt fire. it then goes back to the last good firing time and uses that as its firing time. has anybody heard of this? When he changed the board it worked fine for 3 months and now it's doing the no fire thing again. also sometimes if you reset the power to the unit it will work fine. has anybody ever had the same problem? thanks
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Replies:
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| Coolzilla
|  "Re(1):american standard no heat"
, posted Sun 19 Jun 11:58
It may sound crazy but this has happen to me.It was the reglator.
had good gas press. when the valve was closed but after it open it did not have enough flow.I would have the gas people change this.and a good tech come out with a gas gauge.
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| KRD
| "Re(1):american standard no heat" , posted Fri 27 May 06:19
Try lighting it off by hand. use a barbecue lighter or 12" match. Make sure the orifice feeding the pilot tube is unrestricted. IF the gas pressure is blowing past the ignitor it won't light. I have found the gas pressure extremely high on the pilot tube line only(on gas furnaces)and it wouldn't light. If you don't have a pilot tube line and it lights off on the burners only, make sure the ignitor is in the proper position on the assembly to light. Check to see what the manifold gas pressure is when the gas valve gets energized?
KRD
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| | niko851
|  "Re(2):american standard no heat"
, posted Sat 28 May 09:08
I'm not one to criticize another, since I make my fair share of mistakes in posts, but this recommendation is out of line.
Not only is this obviously dangerous, but we're dealing with Propane on this particular issue. Why take the chance on lighting it by hand when A) Propane is heavier, which means there could be a build-up and no one knows it and B) This is a VERY risky procedure in general.
It's far worth the risk of explosion and while it 'may' light, who's to say that the combustion chamber isn't full of raw fuel? If my co-worker was alive from a similar situation, I guarantee that he's rolling over in his grave. While we'll never really know how it happened, all we know is that the homeowner (who made it out alive since she was in another part ofthe house)said he asked for a lighter/long match to see if he could get it to light manually. She got a new house out of it, and we lost a co-worker.....
Again, no offense intended, but this is NOT a safe procedure and is certainly not one to recommend to an owner who may or may not be familiar with a furnace.
Check your circuit breaker or fuses before calling for service - it could save you $$!!
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| | KRD
| "Re(3):american standard no heat" , posted Sun 29 May 08:46
I've been thinking about what you wrote and the more I thought about it, your right. It was bad advise to give a homeowner a suggestion he might get hurt over. I withdraw the suggestion. I appreciate your concern in bringing it up. MY best guess is that the first stage of his gas valve is not operating properly allowing too much gas pressure into chamber. The 10" of wc is the incoming to the gas valve. The gas valve may not be regulating properly. Thank you again for your concern.
KRD
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| | niko851
|  "Re(4):american standard no heat"
, posted Mon 30 May 08:27
Not a problem KRD; I saw that and immediately thought of Ron, so my first instinct was to ensure the homeowner did not attempt that. As I said, I've made my share of 'bad advice' and have been told such; won't be the first and I'm sure not the last.. It's what we are all here for - especially in this trade, with ever-changing technologies, etc. etc., we are always learning more. Yeah, in the past I would have done that with a standing pilot that was giving me grief - just to heat up the house long enough so the HO was comfortable. Nowadays, even putting Ron's passing aside, I wouldn't even think about 'fooling' a unit via a match, lighter, etc...
Glad to hear that you took that as constructive criticism and not an 'chew-out' or the equivalent. I'd expect someone to do the same to/for me, as they have and will....
Heck look at me with these Stat questions; I believe my track record is 2/11 (two right, 11 wrong)... And I do this for a living - still can't figure out the wiring issues when they are presented... While these forums (not just this one) are excellent places for pro's and DIY's, too little info on the equipment, i.e. just "here's what I have after I pulled the Stat off" is insufficient for (at least me) to get a good feel of what I am up against. Thus, I request more info while 'speculating' the setup. Sometimes I get it, most of the time I don't. So I post "here's what I think, but tell me what is on your terminal block(s) BEFORE re-wiring".
I think I even posted that somewhere (..."why is it that I can't even wire these things in the field"); well, using the 7400D as an example, that thing has to be programmed more than my computer network. Up until recently, via this board, I didn't realize that there are 10 different 'options' for this particular Stat. In turn, my advice was bad. I learned from that, so now I post what I 'belive' it to be, but always ask for the HO to provide models, makes, terminals, colours, etc. before trying it again.
All in all, no harm done; I admire your expertise and your advice on here. At least you had the decency, unlike some, to 'bite the bullet' and understand that (I) was not trying to 'trump' you, just relay the concern over the potential danger. That's a good tech/engineer - one who can and does heed another's comment/concern.
Have a good Memorial day KRD; I get to enjoy the rain up in MI... Glad I chose to do the BBQ yesterday!!
Niko
Check your circuit breaker or fuses before calling for service - it could save you $$!!
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| | KRD
| "Re(3):american standard no heat" , posted Sun 29 May 06:00
I understand your concern. The gentleman said that the ingnitor was glowing which meant all of the safties on the furnace had been initiated and were operational. And I agree accidents do occur. Over the years I have been involved in two explosions. both of which occured when I told the customer to turn on the thermostat to call for heat. I suffered minor injuries. THe thermostat has to glow hot enough to ignite the propane. A person should never attempt anything he/she is not comfortable with. IF that is the case he should problably consult another company to see what the real problem is with his unit.
KRD
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| | beginner
| "Re(3):american standard no heat" , posted Sat 28 May 17:24
I have seen some without eye browse and some no hair on their head. LOL. It is funny, but it is way too dangerous to play around with fire.
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| Xenos
Webmaster 
| "Re(1):american standard no heat" , posted Thu 26 May 08:10
When the gas valve opens what is the gas pressure and is there a delay in the reading? If it's not firing odds are it's gas related.
Xenos.
The best way to escape a problem is to solve it.
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| | hivoltage98
| "Re(2):american standard no heat" , posted Thu 26 May 18:55
it was if i remember correct 10in wc.
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