Fisher & Paykel DE7027J1US Service Manual page 54

1.1.4 Thermistor Operation (Electric Model)
There are two thermistor to control the temperature when running a cycle.
Both Inlet and Outlet thermistor are 100k resistor at 77°C. The resistance of the thermistors decrease every
time the temperature increases.
When the control board detects the temperature is higher that the Outer coil setpoint (due to the inlet or outlet
thermistor), the control board switch off the Outer coil, once the setpoint is lower than the Outer coil low setpoint,
the Outer coil is switch on again.
When both inlet or outlet thermistor detect that the temperature is Higher that the Inner coil high setpoint, both
coils are switch off. Inner coil is switch on when the temperature is lower than the Inner coil low setpoint.
1.1.5 Gas Valve & Ignitor Circuit Operation (Gas Models)
The gas valve system has 2 coils, a booster coil and a main coil, which are operated by thermostats, and a
safety coil. There are three thermostats that operate the temperature control of the gas valve. There is also a
flame detector that operates the coils and the ignitor.
Power is supplied to line L1 both to control board and one of the terminals of the control relays (Gas valve, Mist
valve and Drum).
Power supply is connected to Inlet Safety Thermostat and Outlet Backup Thermostat. If any those thermostats
are open due to an abnormal temperature decrease, the gas valve shall switch off and the dryer will continue the
drying cycle. The gas valve will switch on when the thermostats close its terminals.
The Hi-limit thermostat Power off the unit when is detected an abnormal temperature decrease.
The gas valve assembly operates in two modes, ignition and run. The safety coil is energised during both
modes.
When in ignition, the flame detect thermostat is closed. Power feeds through the booster coil and the ignitor
because these are in parallel circuit, causing ignition. When the flame has heated the flame detect thermostat, it
opens and the valve goes into run mode.
Ignition Circuit
When the flame detect thermostat opens, the booster coil and the main coil are in series circuit, so power is
dropped in the booster and is activated in the main. The ignitor is also dropped in voltage, so stops igniting.
The neutral circuit runs through the motor centrifugal switch and back to the main neutral connection.
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