Whirlpool Duet takes a long time to get hot

[geonjay]

Model Number: WED9400SB0
Brand: Whirlpool
Age: More than 10 years

Whirlpool Duet WED9400SB0. Used to dry the average sized load in 30 minutes. It now takes up to 2 hours. After running for 30 minutes I can't feel that the dryer is heating when I run my hand over the outside...but after an hour it DOES start getting warm..and by the end of the cycle it's gotten up to the expected temp and the clothes are dry. The air flow coming out of the duct seems ok. I've opened the bottom panel and vacuumed out the blower, and lint tray. I plan on doing a deeper dive this weekend using a multimeter, but I thought I'd ask for guidance first - does anyone have an opinion on where I should start? Is this a faulty thermistor?

[denman]

First thing I would check is the heating coil.

Remove the wires from it and measure across it.
It should be in the 8 to 12 ohm range.
Then measure from each side of the element to the case, both should measure infinite ohms.

Next would be the thermistors.

I am assuming that you have the tech sheet.

[geonjay]

I do have the tech sheet and I greatly appreciate your guidance. I do have the tech sheet and I plan on going through the onboard diags first to see if there's anything obviously wrong. I hadn't considered that there could be an issue with the heating element, but that's the first thing I'll check...most of the videos are indicating that I need to fully disassemble the dryer to get to the element properly - is that really necessary just to test it?

I found a resistance across temperature chart for my particular thermistor - should I get fancy and hit it with a blow-dryer to verify a change in resistance, or just go at it from room temperature?
(https://partsdr.com/blog/how-to-test...art-wp8577274/)

Thanks

[geonjay]

I forgot to mention - the dryer has a "Touch Up" cycle that warms previously dried clothes back up and THAT cycle heats right up and only needs to run for about 8 minutes to get the clothes toasty.

[denman]

You might be able to get at the heater connections by just removing the toe kick panel.

It would not hurt to do the more extensive check on the thermistors.

That Touch Up runs OK does seem to show that the heater is OK.
I cannot find info on exactly what/how this mode works.

It is starting to sound like your control board is bad.

[geonjay]

Note to other diagnosing this kind of issue - it's easiest to test the resistance of both the inlet and outlet thermistors from the control board!!!!

The old thermistor had a rattle when I shook it, so I assumed it was at fault. I replaced the inlet thermistor and there no change in drying time. Yesterday I replaced the control board ($235), and the load took a little over an hour to dry. There were no errors reported in diagnostic mode, and the air flow is being reported as 78CFM...and when I go outside and put my hand in front of the dryer air outlet, I can feel the air coming out pretty strong. It still seems that it's taking a LONG time to get warm when I use the "Normal" or "Casual" setting...but the "touch up" setting still gets hot almost immediately. I'm going to keep testing.

[geonjay]

I see in another thread that people are replacing the moisture sensors as part of their "no heat" fix. In diag mode I can test the moisture sensors and they immediately respond when I put my hands on them.