Why do the wires to my dryer's thermostat keep burning off?

Question

I have a Kenmore/Whirlpool dryer that a week ago stopped working. The motor and timing would work, but there was no heat produced. I disassembled the entire dryer and vacuumed and brushed every nook and cranny of lint.

I ordered an entire set of thermostats, including a heating element. When I opened the back of the dryer, I noticed one of the leads to the running thermostat was burned off and the thermostat was charred and deformed. I tested the thermostat for continuity and it read OK. I respliced the wire and still no heat. I tested all the other thermostats and heater coils, including the motor switch and they all passed. I even went as far as testing the timer, which was also OK. I had a hard time believing the molten thermostat wasn't defective when everything I read said that if it has continuity.

Finally, I gave in and replaced only the charred thermostat and it worked. A few days later, the dryer stopped working again, Same problem. I open the dryer and retested all the thermostats and heater. Everything was OK. I also tested the leads at the main circuit breaker and the leads to the dryer.

Figuring at least one of the other thermostats has a false positive, I replaced them all, including the main fuse. It worked again and I thought I conquered the problem. Today, I did a load and found my clothes still damp. I turned on the dryer waited a few seconds and again, no heat.

The obvious question is, what can be possibly be wrong? I never replaced the heating coils, but there was no need to. The only thing I could remotely see wrong was some fine soot on the heating element wires on one side. Could this be a hot spot? I was also puzzled by how the dryer thermostats never read bad. Yes, I did disconnect one of the leads. Obviously, the troubleshooting steps are wrong.

I am at my wits end and a new dryer is out of the question. This dryer worked well for at least two decades and I am determind to solve this problem.

EDIT 2

Since I my last edit, which has been a few years, I have replaced various components in the dryer, including thermostats, wires, etc. I discovered there were burn marks on the wire terminals and the component it lead to. The failure was fairly consistent and wondered why it keeps happening. Lo and behold, the terminals I was using were insulated crimp terminals and it was increasing the resistance of the wire causing it to burn out. I never suspected it because there was no apparent melting of the plastic insulator. I wanted to use non-insulated terminals, but they were very difficult to find and removing the insulation from the terminal connector made an unreliable connection.

EDIT 1

I opened the dryer and tested all of the thermostats and one of the new ones installed above the coils failed. It had no continuity. I replaced it and now it works. What could be causing the thermostats to fail? I should also add that the ducts are totally clean and unobstructed.

My guess is that the replacement parts are of shoddy quality. They were very cheap compared to the ones at Sears. $18 for all thermostats and a fuse versus $29 for just the one that was bad. I am worried that that there may be an electrical problem, venting problem (no changes) or the coil is overheating.

Answer 1

Since I my last edit, which has been a few years, I have replaced various components in the dryer, including thermostats, wires, etc. I discovered there were burn marks on the wire terminals and the component it lead to. The failure was fairly consistent and wondered why it keeps happening. Lo and behold, the terminals I was using were insulated crimp terminals and it was increasing the resistance of the wire causing it to burn out. I never suspected it because there was no apparent melting of the plastic insulator. I wanted to use non-insulated terminals, but they were very difficult to find and removing the insulation from the terminal connector made an unreliable connection.

Answer 2

Clean the built up lint from your vent duct, and also from inside the dryer - from duct connection in the back, to the lint screen.

I bet they are packed.. dryers need to breathe to heat up the air inside, otherwise, the only things heating up are wires and electronics, eventually your house too. Plugged dryer vents cause house fires. Clean the coils in your fridge and freezers as well.

Answer 3

So if venting isn't an issue, there are only a few possibilities. Your problem is either air movement, or electrical.

It sounds to be like you're building up too much heat and/or have a damaged/worn out motor. It's been a long time a nice I've operated on a dryer, but if the hot air from the coils isn't being pulled into the tumbler then you'll start getting sensor faults. Also, a motor which is too worn out will leak black or rust colored powder (which is usually magnet or conductor dust).

As a final point, a damaged motor can cause huge voltage and amperage flux. This could (depending on thermostat design) cause them to become fused and not trip when they should which will, in turn, cause overheating and further damage.

At this point I'd definitely recommend inspecting the motors and make sure that everything is spinning properly. Mainly make sure that any motors rotate quietly and smoothly. Otherwise you probably have shot bearings which will again cause voltage and amperage fluctuation in a bad way. Although usually bad motor bearings will cause a fuse to blow... so it's probably a fully failed motor.

Additionally If your dryer has seen 20+ years of use, I would expect that it needs more than just some fuses and thermostats to be replaced.