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Page | 36
MM10001
Dated 1/1/08
Rev L dated 5/21/15
After sensor is adjusted, place small drop of tamper proof seal on adjustment screw
(this locks in settings so as to not change due to vibration. Use a product that can be
easily removed for readjustment if necessary).
Remove the jumper wire and verify that the temperature is controlled by the aircraft
thermostat from low (approx. 75˚ F) to medium to high (approx. 250˚ F) as
determined by the upper limit switch.
Remove the temperature probe and seal all holes with high temperature silicone.
10.4.2.2 If your heater is not equipped with CD21252…
Upper limit adjustments should be made in accordance with aircraft
manufacturer’s instructions.
10.4.3 Thermostat Control
The thermostat should control the heat output from approximately 65˚ F in the low
position, up to the maximum setting of 225˚ F, ambient, or when the cycling switch limits
heat output. Monitoring thermostat operation can be accomplished by:
Placing voltmeter red probe on terminal #3 with heater terminal strips numbered 1-6
or terminal #7 for terminal strips numbered 4-10 and black probe to ground.
Each time switch calls for heat; Verify rated voltage indicated.
10.4.4 Overheat Switch Testing
In the event of heater malfunction such as overheating, smoke or fumes, disable heater by
turning heater off and disengage the heater circuit breaker. Notify qualified service
technician for servicing. If equipped with an auto reset overheat switch, should the heater
overheat 2 times consecutively (indicated by overheat warning light and or large swings
in temperature) disable the heater as described above and have heater serviced/inspected
prior to further use.
NOTE: In aircraft testing of the overheat switch is not recommended. Test switch in an oven or
on a test stand. Activation temperature is stamped on the switch mounting flange.
To check the overheat limit switch, remove the cycling switch from its mount on the
heater so that it does not read the heater temperature and jumper the thermostat
switch terminals #2 and #3 or #7 and #8.
Restrict completely the ventilating air flow and observe that the overheat switch
shuts down the heater. It should open between 300° and 450°F. This shut off
temperature is also dependent upon ambient temperature and if any air flow.
NOTE: The overheat switch is not adjustable and must be replaced if defective.
After the overheat switch shuts off the heater, remove the jumper wire from the
heater terminal strip and the restriction blocking the ventilation air, and reinstall the
cycling switch. The heater should ignite and function normally within 5 minutes
after sufficient cooling has taken place.
Allow sufficient time for cool down to prevent residual heat from actuating overhead
switch.
Shut down heater and recheck all components.
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