Initial post on 21 Oct 07

Mod# MDG4000AWW. Ser# 10785892WD. I removed vent and front panel. When start dryer, it clicks a couple times then the glow plug lights and the gas flames for about 10-15 seconds- then off. About 30-40 seconds repeats with shorter duration but adequate flame. This second cycle repeats as long as you want. I saw earlier post that was similar except flame quit lighting. I suspect flame sensor. How do I verify. I do have multi-meter but don't know specs to look for. Help is appreciated.

Well I thought this was fixed by cleaning flame sensor. This was not the problem. So I installed the coil kit. This did not fix it. I am starting to think it is the hi limit thermostat. This makes sense to me since the flame lasts the longest on initial start-up, then is on for shorter duration after that. The logic being that the thermostat is warmed the first time from ambient and after that is warm when flame comes on. Again, the flame will relight after 30-40 seconds, just stays on for shorter periods. Initially about 15-20 seconds then down to 4-5 seconds and repeats at that time as long as dryer is on. Anyone know how to verify this with multi-meter or whatever? Should I just replace the high limit thermostat? Any help would be appreciated.

I removed the Hi Limit Thermostat from the tunnel but left the electrical connections in place and ran the dryer. It did not shut off. This confirms that the problem is the High Limit Switch. It is locally available for $22.25. I will post the results later today.

Wrong again! I replaced the high limit switch and it did not fix the problem. Anyone with an idea where to go from here? In the mean time I will pull out burner and clean it. The flame seems to be quite robust, maybe it is too hot? Any ideas would be appreciated. Would really like troubleshooting tips to actually find the problem before I go broke out thinking myself. Thanks

Sounds like an airflow problem to me. Of course, I'm not there to see, but I would leave the vent disconnected and remove the blower housing and clean it very well. Also verify that the blower is working as well

Thanks for the reply. I cleaned that out yesterday and checked the exhaust airflow based on what I read on earlier posts. It does blow out the house vent well and the run is less than 2 feet. I just unhooked the vent at the dryer and tried yet again. There is no difference whether hooked up or not. What next?

Quote:

---

Originally Posted by ge1k

I removed the Hi Limit Thermostat from the tunnel but left the electrical connections in place and ran the dryer. It did not shut off. This confirms that the problem is the High Limit Switch. It is locally available for $22.25. I will post the results later today.

---

It runs fine with the hi limit stat bypassed?

I did not bypass it, I just took it off the tunnel but left the wires hooked up. I will bypass it and try again if you think that is a good idea.

Yes do that. If it runs removed from but not "in the tunnel" it sure sounds like air flow problem. Check that area again for blockage.It sure seems that that area isn't getting proper air flow. I know you said you cleaned it but just check again. Everything else seems proper. Sure wish I could get my hands on this. Got to be something simple here

First I bypassed hi limit therm. Dryer ran well with good flame that stayed lit for several minutes until I shut it off. Then I removed panel over cloths drum and rechecked vent. It
Is clear. I also used a light and mirror to verify duct between burner can (tunnel) and cloths drum also clear. Venting to room with outside vent removed at dryer during whole evolution. Vent at rear blowing well while dryer running. I have replaced both coils at gas valve and hi limit therm. Could I have gotten bad parts? How do I check them? I do have multi-meter. Thanks again for any and all help.

Sounds like it's the hi limit stat. It should read continuity until it opens at the temp marked on stat. you would have to measure temp inside tunnel at the time it shuts down and check again for continuity when stat opens. It will have no continuity when it opens. Is the temp the same as stat rating?

I went out and bought a candy therm. The high limit therm says "L220-40F. I set the candy therm in place of the high limit therm. When I started the dryer the temp rose steadily to the limit on the candy therm of 400 F. What's the next step? Thanks.

I went out and bought a candy therm. The hi limit therm says "L220-40F". I placed the candy thermo in place of the hi limit therm and started dryer. The candy thermo rose steadily to its limit of 400F. I then shut of dryer and stopped flame. What's next? Thanks

I am almost reluctant to claim victory here, but the dryer now works. I did not help myself totally other than not quitting. The problem appears to have been the high limit thermostat. The repair was complicated when I cleaned the burner, then miss-installed it, leaving the inside tab out off its slot. This caused the flame to aim right at the high limit thermo. I noticed the flame originally seemed very close to the sensor so it did not strike me at first, but upon reinstall and retry I noticed flame on for about 15 seconds then off, now very much consistent each time. I then tested the old high limit thermo with a hair dryer, candy thermo, and ohm meter. Initially showed continuity, at about 210-220 degrees switched to open, back to continuity at about 110 then surprisingly open at 160 (vise 220). The subsequent cycles were quite variable but tended to be mostly the same as last one. This did jive with what I saw with this high limit thermo installed. Total cost (minus my time) -High limit thermostat 22.95, coil kit 32.95, and because I can be a klutz, a new, very delicate igniter 39.40 (ouch). Total 94.60. Saved some, learned a lot. Thanks for the help.