Dexter Laundry T-750 C4 Installation And Parts & Service Manual page 80

Heat Circuit
With the blower motor running, 24 VAC provided through the centrifugal switch on the red wire and con-
necting to the violet wire to the computer board gas relay. The temperature sensing probe is found under
each tumbler in the lint tray area and sends resistance values back to the computer board for temperature
sensing. If the computer control senses that the dryer needs heat input, The computer control closes the
upper gas relay which passes the incoming 24 VAC from the centrifugal switch back out on the orange
wire out of the high limit thermostat. The high limit thermostat is normally closed. (The high limit will
open, turning off the heat circuit, if the flame starts moving to the back of the burner housing rather than
being pulled into the burner housing due to airflow issues. In this case the high limit will reset on it's own
once temperatures are reduced). From the high limit thermostat the 24 VAC travels through to the nor-
mally open air flow switch (sail switch) on the brown wire. The air flow switch is pulled closed from the
vacuum created when the blower fan is producing airflow. With the dryer running and the air flow switch
closed, 24 VAC is supplied to the normally closed manual reset over-temp thermostat on the gray wire
and then passes to the black wire out of switch and then goes to the terminal block where it connects to
a violet wire. The 24 VAC then travels to the RC connection at the variable frequency drive. During tumble
mode, this connection closes and the 24 VAC then leaves the variable frequency drive through the RB
connection on the red wire to the 1.5 amp in-line fuse that protects the ignition controller (grey box). With
24 VAC now supplied to the upper ignition controller (grey box) it will then send high voltage to the spark
ignition electrode via the high voltage lead wire (this lead looks like an automotive spark plug wire) and
spark is created. The ignition control module (grey box) simultaneously sends 24 VAC to the gas valve
coil on the brown wire which opens the gas valve and allows gas to pass to the main burner. When the
gas makes contact with the spark, ignition occurs. Once flame is on the burner tube, the flame sensor will
send a signal back to the ignition control on the small black wire that the flame is sensed. At this point, the
high voltage sparking stops and the ignition control module (grey box) will allow gas valve coil to remain
energized and continue burner operation. If ignition does not occur, the ignition control module (grey box)
will spark for 10 seconds before locking out. The control box will attempt 3 times total before a complete
lock out in the event of no flame sense.
Manual Reset Safety Shutoff Over-Temperature Thermostat
The over temperature thermostat is a safety backup for the entire heat circuit and located in the recir-
culation chamber area on the side of the burner housing. If the dryer over heats this over temperature
thermostat opens the circuit to stop voltage from passing to the heat circuit which stops the flame. The
computer board continues to count down and the drive motor remains powered and turning so the basket
will cool down.
Cool Down
Near the end of the cycle at the preprogrammed time (2 minutes factory setting - adjustable) the comput-
er board will open the gas relay contact. This happens for the remainder of the cycle. The drive motor will
continue to run but without heat. The gas light on the computer board should not be illuminated anytime
the computer is in cool down mode. This cool down period allows the clothing (zippers, snaps, etc.) time
to cool down to a temperature that is easily handled by customers.
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Part # 8533-120-001 9/21