LG Dryer DLE3777W blowing F140 thermal fuse

[jvf]

Hello,

I’m trying to help a neighbor whose dryer has started blowing the non-resetable thermal fuse shown as F140 on page 39 in the service manual. I think the unit is at least three years old but I’ll have to check. In other words, it’s not new. It’s stacked and squeezed into a small alcove which makes inspection difficult. The manual’s terms are confusing. Somewhere it says F130 is high limit thermostat and F140 is a dryer high limit thermostat. ??? Whatever.  

  Having tested and repaired a number of items, I’m running out of ideas. Let’s review the highlights:

 1) Neighbor had somehow managed to take off the power cord and one terminal was pretty fried with only a few strands connected. I’ve seen this many times with high current connections. So, one leg of the 240 absent? Sadly, not. I repaired the cord and properly reattached it (assembled the strain relief connector like it should be). But, no heat.

2) Neighbor had found a repair video which showed possible thermal fuse causing problem and how to replace by disassembling unit. Trying to avoid the hassle of unstacking the units, I performed my best imitation of a veterinarian servicing a cow by removing the exhaust tube, reaching inside and testing the thermal switch which was blown. Why?? I jumpered the connections and we had heat. He got a 4 pack from Amazon and I replaced the failed component. While squeezing my way around to the back of the unit, I had noticed the vent exhausted through the floor near the corner. Curled up on the floor then rising up and over to the vent was the tube of death. OK, possibly we didn’t have enough air flow. So, while waiting for parts, I put in a proper transition vent. Dryer worked OK for about two weeks then stopped drying clothes.

 3) What if there was a second tube of death curled up underneath the house? I’ve seen it before. I put it on air dry and went under to take a look. Everything was fine with a 90 and short length of duct leading to the vent flapper. I measured 140cfm so air flow is fine.

4) Some say the resettable fuse (F130) can stick and cause the other to blow. Well, if that one is cycling it still indicates a problem. Nonetheless, I removed it, attached a thermocouple and tested it with my heat gun. It cycled near its specs a couple of times and so I put it back. Before installing the second F140, I super glued a thermocouple to it so we could observe temperatures in operation.

5) I measured current draw of both the motor and the heating elements and both were right on spec. This leads me to believe there is no short to ground of the heating element.

6) We turned on the dryer to normal and watched temperature seen by F140. We observed cycling with max of about 100 deg C. But, dryer was empty. We put in a damp towel and set it to manual with max temp. We observed cycling with 120 deg C max. Since temperature was cycling, this meant controller was turning element on and off but I watched current just to be sure and could observe current dropping to 0 when temp started cooling down.

7) Looks good but we need a real test with full load, I said. Unfortunately, I was away for first dryer load but it worked fine. I was present for second load but temperatures immediately reached 200 deg C and climbing. I figured (correctly) that the super glue gave up and the thermocouple had broken away and moved nearer the heating element. Bummer. Due to the major hassle of reattaching the thermocouple I told the owner to just dry the load and I’d come back and fix the thermocouple. Well, the thermal fuse blew and the clothes never finished drying.

We only have two bullets left. Before using one, I plan to jumper the circuit and, as suggested by some,  measure air temperature coming out of the dryer expecting to see 160 F +/-. First, I’ll air dry only and next we’ll fill ‘er up with damp somethings and run it like they do.

I’m wondering about bad drum seals or failing door seals letting in cold air, etc. and fooling the temperature controller so I’ll be checking these (after sucking it up and unstacking the units). Is there something about LG dryers that causes a certain condition to occur? Am I overlooking something obvious? It wouldn’t be the first time I’ve complicated a simple problem. By now you’ve probably realized that I’m not an “appliance repair guy”. I’m a retired electrician with a fair amount of experience with machinery that uses these types of sensors and controls (blame the brain last) and am interested in appliance repair. But, I don’t have any practical experience with these particular machines so I’m going to school with this one.

Thanks,

jvf

[Brian B]

Thermal fuse failure could be caused from air flow issues. Check the blower wheel if you managed to unstack it

2. Check the thermistor both at the board and at the thermistor if it out of range at room temp or at higher temp, it could be the board or the thermistor.

3. No lint anywhere!

4.if it has a timer, the timer motor should be off while heater is on and on when heater off

 

 

 

[Vance R]

The thermostats is this dryer are basically safety devices. The temperatures are control by the board based on information from the thermistor.  Check the thermistor using info from page 22. I would recommend taking the dryer down and taking it apart.  Split the heater can and remove the lint. If the vent was restricted the  heater can will have lint packed inside. Have no clue why these don't catch on fire. 

About page 39, that is the explode view for parts. The "F" number are just locator number to reference the parts list to get correct part numbers. Page 14 has specs for thermostats.

[16345Ed]

Don’t forget to check lint screen. Does water flow through it?

[WOOKIE]

Also, There is a service bulletin (6-Nov 2005) for the dryer.  " When a Hi-Limit thermostat is replaced, a safety thermostat must also be replaced. "  Search "DLE7" to find it.