Hawker F20/4H1C-R Operating And Maintenance Manual page 35

Test 2: Thermostats below ambient temperature
CAUTION
Spraying human skin and tissue with coolant causes serious injuries
(burns) by freezing. Read safety instructions about cooling spray.
2.a Identify the thermostat type and its switching temperature
according to the Appendix 4
2.b Disassemble the battery to the state necessary to remove the
switch assembly together with the corresponding connector
2.c Fix the link with the thermostat on the test fixture
2.d Connect the relevant pins in the interface connector of the
thermostat assembly to an ohmmeter
2.e If necessary, connect a thermocouple on the link as close as
possible to the switch
2.f Record the ambient temperature
2.g Record the measured thermal switch position at ambient
temperature (opened or closed)
2.h Cool the fixture with the freezing spray to a temperature of 10°C
below its switching temperature and maintain it at this level until
the switch operates
2.i Record the corresponding temperature when the switch operates
2.j Stop cooling the link, and allow the link temperature to rise whilst
monitoring the ohmmeter for the thermostat to switch to its
normal state
2.k Record the temperature at which the thermostat switch to its
normal state
2.l Identify faulty switches that do not switch or exhibits irregular
switching operation
2.m Refit the switch assembly on the battery,
Test 3: Thermistors
1. Connect the terminals of the ohmmeter to the pins of the
thermistor.
2. Measure the temperature of the link (plate) with the thermistor
is fitted using an electronic thermometer
3. Measure the resistance.
4. Compare the measured temperature and resistance of the
thermistor with the curve in the corresponding IPL
5.
A properly functioning positive temperature coefficient thermistor
will show a smooth and steady increase in ohmic resistance.
Consequently a properly functioning negative temperature
coefficient thermistor will show a smooth and steady decrease in
ohmic resistance. Using a suitable heat source heat the thermistor
link (plate) ensuring not to exceed a temperature of 70°C
(Alternatively the link can be cooled with freezing spray).
6. Signs of faulty thermistors:
a) Steady reading that does not change
b) a reading of zero
c) reading of infinity are all indications erratic reading.
The document reference is online, please check the correspondence between the online documentation and the printed version.
Replace the thermostat / thermistor assembly in accordance
with Task 10.4.
Replace the thermostat / thermistor assembly in accordance
with Task 10.4.
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