Test #4: Moisture Sensor - Whirlpool WETLV27HW0 Service Manual

WARNING
Electrical Shock Hazard
Disconnect power before servicing.
Replace all parts and panels before operating.
Failure to do so can result in death or
electrical shock.

TEST #4: Moisture Sensor

(long vent models only)
Theory of Operation
The "C" version dryer control system consists of an electronic
control board located in the console area and a moisture
sensor attached to the lint screen grille inside the dryer drum.
The dryer control system measures the resistance across the
moisture sensor during the automatic dry cycle. The electronic
control board turns power to the timer motor on and off based
on input from the moisture sensor.
When a cycle is selected, Timer Contacts C - B will be closed.
This applies 120 VAC through the orange/black wire to the
electronic control board. Timer Contacts T - X will be open
if the selected cycle is not a timed dry cycle, so there is no
alternate path for current flow through the timer motor.
The electronic control looks at the input from the moisture
sensor to see if the clothes are wet or dry. The moisture sensor
MOISTURE SENSOR CIRCUIT
MOISTURE SENSOR STRIP CIRCUIT
L1
BK
TIMER
CONTACT
OR
BK
C B
BK
For Service Technician Use Only
ELECTRONIC
OR-BK CONTROL
C-VERSION
Y-R W-BK
G-Y
TIMER
MOISTURE
SENSOR MOTOR
1900-2900 W
Figure 1 - Moisture Sensor Strip Circuit
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 and any Timed
Dry Cycle, Timer Contacts T - X will be closed. This will allow
the timer motor to advance regardless of the condition at the
moisture sensor. Timer Contacts T - X bypasses the electronic
control.
Test Procedure
This test is performed when an automatic cycle stops too
soon, or runs much longer than expected.
NOTE: Overdrying may be caused by a short circuit in the
sensor system.
1. Unplug dryer or disconnect power.
2. Access the sensor terminal by removing the front access
panels. Disconnect the moisture sensor connector.
3. Access the C board moisture sensor connection by
removing the C board. Check continuity between the C
board harness moisture sensor connection (pin 3) and the
moisture sensor connector.
¾ If there is continuity, go to step 4.
¾ If there is no continuity, replace the main harness.
4. Measure the resistance across the outermost contacts of
the connector.
¾ If a small resistance is measured, clean the two metal
moisture strips inside the drum. If a small resistance is
measured after cleaning, replace sensor harness.
¾ If a small resistance is not measured, replace the C
board.
T-W
LBU
OR
T X
TIMER
W
CONTACT
5-Pin Connector
N
W
DOOR
SWITCH
W
Figure 2 - Electronic Control Brd
27" Stacked Laundry Center
TESTING – DRYER
4-13
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