Gas Dryer Not Heating
Appreciate some help re. testing my gas dryer radiant/flame sensor,
Whirlpool/FSP P/N 338906. My understanding is that it should be closed circuit when no light shining on the window, and open-circuit with light. Mine worked that way at first, but after I shined my 75 watt trouble light on it for a while, when I remove the light and put black tape over the window, it goes closed circuit?, BUT when I now shine my trouble light on it, it WON?T go open circuit even after several minutes. Did I zap it? How much light should be used to test it? Testing done out of dryer.Answer
This is Shawn creator of www.applianci-repair-it.com. I have never used a trouble light but this is how I would test a gas dryer. Start the dryer and watch the igniter. The igniter should glow red for some time (30-120 seconds or so) then the igniter will go out and the flame should ignite instantly. If the igniter doesn't glow red use an ohmmeter to check for continuity across the igniter with the dryer unplugged and the igniter disconnected. If the igniter checks ok check the thermo fuse located on the duct in the back compartment it should have continuity across it. If the igniter glows but after a few minutes doesn't go out the flame sensor is bad (the part you are describing above). If the igniter glows and then goes out the coils on the gas valve are most likely bad. Also if the dryer is heating intermittingly it is most likely the coils on the gas valve. All of this and more are on this page Gas Dryer Repair
I want to THANK YOU and a couple other folks whose Internet sites I've used to learn how my gas dryer works, which has allowed me to repair it. Its ACTUAL PROBLEM was that one of the gas valve coils would go "open circuit" when the dryer got hot. I probably would not have known to test the coil resistance WHILE HEATING IT with a heat gun, had I not been pointed to the probability of bad coils in various Internet sites.
However, while I had it a part, I figured I should test and consider replacing any related component that might be bad or suspect, which is why I tested the Flame Sensor. UNFORTUNATELY, one site that talked about the Flame Sensor, said that it would switch (to open circuit) if/when you shine a flashlight on it. Mine would NOT switch using a flashlight, or even with my 75 watt incandescent trouble light shining on it, so I thought it might be bad too. Fortunately, a different Internet site NOW informs me that it takes HEAT from the igniter to cause the Flame Sensor to switch, so I went ahead and installed my (suspect) Flame Sensor, and it has been WORKING FINE through about 6 dryer loads today. Again, THANK YOU for your time to answer my e-mail, AND ALSO for putting your nice website together. I have book-marked it, and will share it with friends.
Hi again Shawn,
I actually wasted a moderate amount of time trying to check
the flame sensor per the erroneous instructions (aka flashlight). Also, the following websites gave resistance specs for these coils, but my
BRAND NEW FSP ones were technically out of spec, as the 1->2 resistance I measured with my name brand digital ohm meter is 1415 (vs. 1365 +/- 25) and the 1->3 resistance measured was 590 (vs. 560 +/- 25) and the resistance across the 2 wire coil was 1298 (vs. 1220 +/- 50), but what was I going to do, as had to get the unit running before the family "killed me". Do you have any comment as to the resistance values/specs? FYI, I used the heat gun, because my problem was intermittent, and with my newer style Whirlpool dryer (which does NOT have the ~8" high access panel across the front bottom like my old one did), I was not able to make measurements with the unit running and not heating. Was glad to see the coil go "open circuit", but then as say, got mislead re. possible bad flame sensor.
THANKS AGAIN FOR YOUR TIME AND HELP!Answer
You are welcome! Glad to hear you got it working!! I have never heard (nor do I believe) that you could shine a light on the flame sensor to get it to work. It works from the heat off the igniter. That was a very good idea to test the coils while heating them with a heat gun. I usually don't test them at all because they have a tendency to intermittently check good or bad. Those coils consistency give false positive readings so I just replace them for three reasons; one if the igniter goes out but the flame doesn't light, if it heats sometimes and sometimes it doesn't or it starts heating then quits. These scenarios are almost always the coils. With that being said I love your test with the heat gun it will confirm that they are bad.
As for the resistance value I wouldn’t worry about it especially if the dryer is working now! I try not to get caught up in things like resistance values and things like that especially on my website. I try to keep thing as simple as possible on most things 99% of the time if it is not an open circuit the device you are testing is ok. However this isn’t true all the time. I normally don’t even test for ohms across these coils I just check it as I describe in both of my other e-mails because I found them to test very inconsistent.
As for you spending more time on the repair as you should I think that it is ok because you managed to repair it yourself which is what you set out to do! I wouldn’t have spent a lot of time on the flame sensor simply because I understand how they work and I know they give very little trouble. I am not sure where they came up with the idea that shining a flashlight on it would work I would think it would have to be a hot light then again I never tried it. I would have to see it to believe it. In any case I am glad that you got it repaired