Kenmore Dryer 90 Series - Heating Element Won't Stay On

[chingo]

Old Kenmore Elite 90, Model 110.60954990.
The heating element will turn on, but will not stay on for more than 30 seconds. It will sometimes kick back on after a few minutes, but again for no longer than 30 seconds.
This happens with both Timed Dry and the Even Heat.


Took the whole thing apart. Cleaned out all vents, was not all that dirty.
Replaced all common failure parts anyway (See below)

Tested all the elements with multi-meter. All seemed fine.

• Voltage to unit at 240 checks out
• Timer: checks out
• Thermistor on blower assembly: okay upon testing, replaced anyway
• Thermal cutoff: okay upon testing, replaced anyway
• Hi-limit thermostat: okay upon testing, replaced anyway
• Heating element: checked, is okay
• Motor switch: checked just in case, is okay

Ran it without vent attached to ensure no blockage and plenty of ventilation.

I'm at a loss here. Only thing left would be one or some of the elements on the console panel.
Those are a bit more expensive just to hope a replacement would work.

What is telling the components to shut off the heating element after only being on and glowing for 20-30 seconds?
 

[dfphoto]

didn't look at the schematic but seems like you have an element short?

[chingo]

I've tested the heating element for continuity.

Would the element still heat and glow for 30 seconds if it was shorted?

9 minutes ago, dfphoto said:

didn't look at the schematic but seems like you have an element short?

 

[dfphoto]

well look at it closely look for black areas if it gets hot it can sag and touch. ask Dr H he can figure it out.

[chingo]

On 3/5/2024 at 4:07 PM, dfphoto said:

well look at it closely look for black areas if it gets hot it can sag and touch. ask Dr H he can figure it out.

How do I ask Dr. H?

[dfphoto]

In my mind, I'm looking at the chart if the heating element gets too hot and touches it could create more heat and trip the hi-limit or something with the relay what are you seeing at the heater. You have to attack this take it apart and check it out. take pictures

[Guest]

On 3/5/2024 at 5:07 PM, dfphoto said:

well look at it closely look for black areas if it gets hot it can sag and touch. ask Dr H he can figure it out.

Help me understand what you meant by this

[dfphoto]

You know a lot and you like to help others, I am unsure what this persons problem is and I figure you can help him figure it out.

[chingo]

So if we know all the elements are in working order, and the element CAN heat up, but keeps tripping off...
it must be getting too hot and keeps tripping the thermal cut-off...
I have not replaced the thermal fuse, but it tested okay.
My understanding is the heat/dryer wouldn't work at all if it was the fuse.

I tested the heater relay voltage per the tech sheet, and it checks out.

[L. Ron Hoover]

My approach would be to rule out an intermittent open circuit in the heater coil.  It's possible for the coil to be broken in such a way that the broken ends touch each other or one broken end is grounded when cold.  As the coil heats, it moves and continuity is lost.  It cools down and continuity resumes.  a visual inspection should show carbon.  Once that is ruled out, I would suspect the small circuit board that the thermistor is connected to or its wiring.  Sounds like its calibration is way off.

[chingo]

1 minute ago, L. Ron Hoover said:

My approach would be to rule out an intermittent open circuit in the heater coil.  It's possible for the coil to be broken in such a way that the broken ends touch each other or one broken end is grounded when cold.  As the coil heats, it moves and continuity is lost.  It cools down and continuity resumes.  a visual inspection should show carbon.  Once that is ruled out, I would suspect the small circuit board that the thermistor is connected to or its wiring.  Sounds like its calibration is way off.

Thanks I will triple check the element again. Hopefully that's it since circuit board testing or checking wires might be past my ability.

[L. Ron Hoover]

Basically you have to find which component has the line voltage across it's terminals while the heater is off.  If it's the heater coil, then that's the problem.  If its the relay, then it's either the relay, the board, the thermistor, or its associated wiring.

[chingo]

1 hour ago, L. Ron Hoover said:

Basically you have to find which component has the line voltage across it's terminals while the heater is off.  If it's the heater coil, then that's the problem.  If its the relay, then it's either the relay, the board, the thermistor, or its associated wiring.

What's the best (and safest) way to bypass the door/front plate assembly so I can run the cycle for quick testing with the dryer taken apart? Just a paperclip?

[dfphoto]

You might start over and check your vent system for lint clean it out all the way to the end.... then work into the machine. I don't want the liability to tell you how to bypass the door its 240v that's not something I would be messing around with...

[chingo]

Fair enough. Was hoping to test the voltage across the terminals easily.

[dfphoto]

You  have all the information you need to figure it out... that one guy and I said the same thing, Now I've told you to check the vent clean it out... then test your voltage but I didnt tell you that.. The manual says so... people are not going to say do 1-2-3 you gotta figure it out..

[DADoESTX]

@chingo The thermal fuse on the heating element box is a one-shot protector.  It melts at 352°F, and then must be replaced.  The high-limit thermostat that's also on the heater box protects the element from overheating if it runs too hot due to obstructed airflow (triggers at 250°F, auto-resets at 170°F).  The thermal fuse functions as a fail-safe for the high-limit thermostat, and also as a protector if the element shorts to ground (breaks or sags and touches the frame or heater box) in which case it may energize when the dryer isn't running, thus the need for the thermal fuse.

The thermal fuse on the blower housing is likewise a one-shot protector for the thermistor that controls the drying temperature, if the air temperature coming out of the drum exceeds safe limits (91°C / 196°F).

[chingo]

It turns out I am able to keep the heat going by keeping the temperature selector on medium heat. I have been able to run a handful of loads through the dryer as long as I keep this temp setting.

So when a higher temp setting is selected, something is allowing the heating element to get too hot and is what kept triggering the thermal cut-off.

What would be responsible for this malfunction?