[Jonathan]

I've poked around and tested a few things. All of which leaves me scratching my head...

The dryer spins fine, the blower blows, no strange noises. I've vacuumed out the whole airway (annual event in my house but I did it again anyway). I've replaced the cycle dial & timer already. We don't use dryer sheets, so the lint filter should be pretty clean. That's the good news.

The bad new is the dryer won't heat more than once per cycle if there are clothes in the dryer. On a whim, I ran the dryer with no clothes in it and watched the burner. Pressed start, watched the burner kick on and blow a nice blue flame. The leads me to believe everything is working OK at the front of the dryer: gas valves, igniter, & flame sensor. The dryer door warmed up, the flame went out. The door cooled down, and the cycle repeated. I gave up after watching it restart itself three times without me touching anything. Then I put in a batch of clothes (not too big), the flame kicked on at the beginning of the cycle, ran for about a minute, then kicked off and refused to restart: no igniter glow at all, no valve noise, nothing.

I infer that the igniter and flam sensor are working OK based on seeing them actually work a few times in a row. Is this a good inference?

I checked the continuity of the valves after I stopped the load spinning just because it was easy - no resistance on any combination I tried. The one web site I saw suggested resistance of ~1KOhm on a couple legs, but I didn't see any. If the valves weren't working at all, then I would assume I'd smell gas or there would never be any flame. Since I don't smell gas and I can hear them open/shut, I infer they are working OK.

I haven't checked anything else yet.

I also cleaned the window on the flame sensor with a little rubbing alcohol - didn't appear to be too dirty and had no effect on the symptoms.

This leaves the thermal fuse and the cycling thermostat so far untested, but why would these work when there are no clothes in the dryer and not work when there are clothes in the drum?

I'm planning to work down the list I found online tonight. Any special ideas what to do next besides "check everything"? Anyone seen anything like this before?

[denman]

Sounds to me that it is not sensing the flame

It gives it a little time then the control says OOPS no flame I had better turn the gas off. Depending on the controller it may try this a couple times before it decides that there is definitely a problem and gives up.

[Jonathan]

OK, I got the front off it and traced the wires.

I have a pair of grey wires going to a part labeled 6J410184C, 3-06604, HBB4, which I take to be the thermal fuse. OhmX1=0, so I think this is good.

I have a bundle of 5 wires going to what I take to be the cycling thermostat, part number L150-25F, HTR120V, 3-07250, 329301, 69T13, 9217. There are 5 contacts connected to a Yellow-Black (Y-BK), an Orange (O), a White-Red (W-R), and two purple wires, jumpered together, P1 and P2. I tried all combinations: everything is Open (OhmX1=infinite) except Y-BK to P2 (OhmX1=0). Physically these connections are at extreme opposite ends of the thermostat (longest width apart). I infer from this that the cycling thermostat is bad and needs replacing.

Igniter OhmX1=0. Seems to work OK too.

Flame Sensor OhmX1=50. Is this good or bad?

Gas valve coil, 2 connections, OhmX1=0. Is this good or bad?

Gas Valve coil, 3 connections - hold so the connections point up:
left and middle terminals, OhmX1=0. Is this good or bad?
left and right terminals, , OhmX1=0. Is this good or bad?

Any thoughts? Anything else I should look for? I don't see any other wires running anywhere else, so I haven't identified any other thermal thermostats.

And thanks in advance!

Jonathan

[denman]

I have very little experience on gas, most units electric, around here

Your cycling thermostat is probably OK
One set of leads is the contacts
The other set of leads is a small heating coil, just cycles it faster
Try a higher scale, the coil may read infinite at 1X try 20K, depends how your meter is scaled.
In any case it should not give you the symptoms you have.

Not sure about your other questions and I do not want to steer you wrong

Here is a helpful link
Dryer Help Sections, repairing dryers, Kenmore, Whirlpool, Maytag, Inglis, GE, Frigidaire, White Westinghouse, Magic Chef, Norge, changing a 3 prong cord to a 4 prong cord, no heat, electric dryers, gas dryers, how to take apart my dryer, what can st

[Jonathan]

I had to relearn how to read my analog ohmeter (it's been 20+ years since I've had to read anything other than open/continuous!):

Gas valve coil, 2 connections, R=1225

Gas Valve coil, 3 connections - hold so the connections point up:
left and middle terminals, R~=1800
left and right terminals, R=550

Based on that, I think the coils are good (and they work, too!)

On the thermostat, I'll try that again tonight.

[Jonathan]

Oh goody! More news.

First off, good call on asking me to change scale. The W-R to P2 connection is actually 7500Ohms, not infinite (10K scale). I also checked all the lugs to ground (dryer case) and found opens everywhere. I'm not sure what all this means as far as the cycling thermostat.

I found the overheat thermostat - it is continuous through both lugs.

I also layed down and watched it cycle for a while. The first time the gas flame came on three times within 5 minutes, then the igniter heated with no flame and no solenoid noise twice before I stopped it.

I then took the door off, checked the flame sensor again (still continuous, 0 Ohms), the overheat sensor, and the cycling thermostat - same results even though they are supposedly "warm".

I put the door back on, ran it, and the igniter failed to find gas on the second try.

At this point I'm thinking the gas valves need replacing. Can anyone think of anything else I need to look into before I start shopping for parts?

Jonathan

[denman]

Your cycling thermostat measures OK
As do all the others
They should all be 0 ohms at room temp across the contacts

Here is a link on the coils and the sensor
Gas Dryer Repair Guide: How to Check the Flame Sensor - ACME HOW TO.com

This one looks like it has a very good explanation
DRSNews 3-04 - Gas Dryers - Diagnosing, Converting to LP

And one more just for good measure
The Whirlpool and Kenmore gas dryer flame sensor

By the time you are done, you are going to be a pro at this but probably not want to look at a dryer again for a couple years

Good Luck

[Jonathan]

I'm not afraid of learning new things. ;-)

I'll retest the flame sensor. I just thought of way to do that while it's running which would be a better test.

I'm still concerned about the cycling thermostat. When I ohmed it out, everything was Open, not Ohms=0, except Y-BK to P2 (0 Ohms) and W-R to P2 (7500 Ohms). If I read your last post right, everything should be 0 Ohms if this part is in good shape?

[denman]

No: they should not both be zero ohms

The cycling thermostat has contacts and a heater in it
The contacts should measure 0 ohms at room temp
The heater should have a resistance same as any other heating device

The way it works is that the heater adds heat to the bimetallic contacts forcing them to cycle on/off more often than if the just received heat from the dryer.
Used for a low heat setting.

[Jonathan]

Hmmm. I looked for a schematic of the thermostat a little bit - I'll have to try some more. I'm not convinced I have a good or a bad one yet.

News on the flame sensor: I have been looking for an excuse to go get a new tool, so I went and got a clamp meter. I watched the power to the flame sensor. Normally zip. When the igniter is heating, the amps build up to 4.2 A and then cut back to 0A when the igniter is the hottest. The cut to 0A is accompanied by the gas valves going thunk and the burner igniting when everything is working.

When everything is not working, the sequence is exactly the same except that the gas valve never goes thunk and there is no flaming gas. Ergo, I have at least one bad gas valve and one good flame sensor. Gas valves are more expensive...