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Moisture sensor

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MajorApp:
 I need a lesson in moisture sensors. How to test them.

Model 110.67622600

Repair-man:
Basically, this type of moisture sensor (2 metal bars) is merely a pathway to ground for the timer circuit or electronic control. You'll notice that one of the wires to the sensor  comes from the control, the other is a green ground wire to the front bulkhead.

When a damp load contacts the 2 bars, there is a temporary short to ground created. This causes the resistance to decrease from the timer motor and go toward ground, causing the timer motor to stall briefly. In total electronic units, the control counts the frequency of contact with the damp load and will not turn off the dryer until there are no more wet touches across the sensor bars. The electronic control looks at the input from the moisture sensor to see if the clothes are wet or dry. The moisture sensor will show continuity (short) if the clothes are wet and show NO continuity (open)if the clothes are dry. If the clothes are wet, the Triac on the electronic control board will block power to the timer motor, and the timer motor will not advance.
If the clothes are dry or there are no clothes in the dryer the Triac on the electronic control board will allow power to flow to the timer motor causing it to advance. During the last 10 minutes of the Regular Cycle, (the last 15 minutes of the Permanent Press Cycle) and any Timed Dry Cycle, Timer Switch 0 will be closed. This will allow the timer motor to advance regardless of the condition at the moisture sensor. Timer Switch 0 bypasses the electronic control.

Did this help?

What is the nature of the problem on this model?

JWWebster:
If too much fabric softener or various items gum up the sensors the capacitance will not be read correctly and resulting in continuous running equipment.

Repair-man:

--- Quote from: JWWebster on July 22, 2009, 09:20:04 PM ---If too much fabric softener or various items gum up the sensors the capacitance will not be read correctly and resulting in continuous running equipment.

--- End quote ---

There is no "capacitance", and if the sensor could not be sensed the dryer would shut off too soon, leaving a damp load.

JWWebster:
Well the one I was thinking of mounts inside the drum underneith the filter and measures the electrical resistance through the clothes to the dryer drum. As moisture is removed from the clothes, the resistance increases for a precise dryness level.

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