Gas Dryer Poor Performance

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I think this is the newsgroup traditionally used for appliance questions, so hopefully this is acceptably on-target.
The Kenmore-branded Whirpool dryer (110.79912900) hasn't been doing well in recent months, taking unacceptably long to dry loads while still clearly putting out some heat. Obviously, the first thing I did was to pull the skins, clean out the usual amount of congealed lint inside the filter screen area, and leaf-blower the entirety of the interior. Happily it is right up against the exterior garage wall with a real short duct to the outside, and that is totally clean.
I observe that when started, the igniter comes on, I get a nice flame for three or four minutes, and then it goes out. But unlike the typical (as I understand it) coil failure, the process repeats, but not for several minutes. No wonder the drying takes so long - the gas should be burning considerably more frequently than I'm observing and it's thus blowing lukewarm air for much of the cycle.
I first thought that this still could be an issue with the coils, and found a web site that tabulated typical resistance values to the various combinations of terminals on the three-post and two-post coils. To my surprise, all were dead on. So I assume the coils are fine.
So now it's time to ask for some assistance. My next thought is the pair of thermostats inside. I haven't pulled them or tested them in any way yet, as they're harder to reach than the coils. Is this a valid next step? Would it be most likely the low-temp (155 degree) thermostat not reacting quickly enough to the drop in temperature after the flame has been turned off?
Advice welcome.
Art
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On Feb 23, 1:55 pm, snipped-for-privacy@unisys.com (Arthur Shapiro) wrote:

It could also be the timer is intermittent. My timer on my gas dryer had bad contacts inside, these contacts is what completes the circuit so the gas valves can open, and let the gas come on. So just keep that in mind too while troubleshooting. How does it dry in the other cycles? Try the "Timed" cycle. For some reason, when I had the timer problem, it would be fine in "Timed" mode, but not "Auto". The contacts are configured different for each cycle.
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Thanks for the suggestion. I should have mentioned that behavior on "timed" is equivalently bad to that on the normal settings. At times I have felt that the "high" setting performance is worse than the next-lower "permanent press" setting, but I'm not totally convinced of that.
Art
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On Feb 23, 1:39 pm, snipped-for-privacy@unisys.com (Arthur Shapiro) wrote:

Sure sounds like a thermostat issue tio me.
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Arthur Shapiro wrote:

1st thing I'd do is drag it outside, and blow out every air passage and all spaces around the drum thoroughly with an air compressor or leaf blower. I've fixed 2 slow drying dryers that way.
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That's a novel approach. Of course, dryers get clogged with lint. And air flow is a concern.
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That's why I stated that I'd leaf-blowered it inside and out. I hit it as best as possible from the output end and from the filter end after removing the filter shroud. The thing is pretty clean.
I ordered both thermostats today, although it isn't immediately obvious to me how to get to the rear one, and even the front one is going to be awkward. I fear the entire cabinet has to be removed, and that process isn't blatantly apparent.
BTW, leaf blowers do wonders on desktop computers. I've had folks concerned about static electricity affecting delicate componentry, but I personally haven't had any issues.
Art
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On 2/23/2010 19:58, Arthur Shapiro wrote:

My guess is the valve coils. You can confirm by measuring the voltage coming in to the coil assembly, which includes the ignitor and flame sensor. If voltage is present after the gas cuts out prematurely, the trouble is in the valve assembly.
If the trouble isn't with the thermostat(s), your parts supplier may take them back if the packages are unopened.
--
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Arthur Shapiro wrote:

I had the same problem with my gas dryer. The coil resistance read fine but the gas would only stay on for a few minutes. When the coils got warm though, one of them went open circuit till it cooled off. I bought a new set of coils at the local appliance parts store for about $25 and everything worked fine. The coils fail frequently so they had a supply of them right up front.
-Mike
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Thanks for the report. I guess I'd best wait to see if the thermostats fix the problem. If not, you've convinced me to try the coils.
Art
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It is not the thermostats. You are wasting your money. I can think of only two reasons to have your symptoms:
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It is not the stats. You are wasting your money. I can think of only two reasons for your symptoms:
1. Coils. They are almost impossible to test via ohms. Just replace them as pair. 2. Restricted ducting. But you said that the vent connector is short to the outside. So, go to #1.
NSP
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On Feb 24, 11:53 am, snipped-for-privacy@unisys.com (Arthur Shapiro) wrote:

I had the same problem. I went to a local appliance parts store and asked for the thermostat. The nice lady behind the counter asked me what the dryer was doing.
When I described the same symptoms as you she said "I could sell you a thermostat for (I forget how much) but it's almost always the valve coils and they are much, much cheaper. If it were my dryer, I'd try the coils first."
I did, and she was right.
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Oh well...they came in today's mail, so I might as well install the thermostats. Got 'em at a quite reasonable price on eBay, so I've wasted less than twenty bucks. Getting to them looks like quite a hassle, but...
When / if that fails to cure the problem, I'll pick up a set of coils and install them.
If things are still bad, and I don't expect that, is it time to call in the pros?
Art
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Arthur Shapiro wrote:

That's a question for alt.hvac. :-)
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Worth noting, that alt.hvac is a usenet group similar to alt.home.repair; the folks who post there are HVAC professionals, and who answer questions on money saving, from home owners.
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Evil ! Evil ! Evil!
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Like with most jokes. I have to pass it along, or I'm left holding the bag. It would be unpatriotic of me, not to.
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cliqueish, unfriendly group on Usenet, unless it has changed in recent years.
I was quite busy all weekend, but hope to tear the dryer apart during the week. There's apparently no way to access both thermostats without pulling the cabinet.
Art
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Alternating havoc hasn't changed a bit. You can depend on prompt, courteous replies to questions about replacing thermostats on a Do It Yourself basis. Replies which which will make you think that your own grand mother is writing them. You know, the granny who totes a shotgun, brews her own moonshine, and learned her speech patterns and cadence from barending for the Pakistani military.
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