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|  MIL-H-3771C
4.5.4.6.4 Overheat control. Short-circuit the cycling-control thermostat
or otherwise prevent it from cutting off heater operation. With the heater
in normal operation, control the cod-ant-outlet temperature 80 that it
rises slowly until automatic cutoff and purge occurs. Reduce the temp-
erature of the coolant at least 50 F below the overheat cutoff point
(see 3.8.4.2(e)). When separate coolant pump is used disconnect the
coolant pump from its power supply and valve-off coolant circulation by
means of a valve near the heater inlet. On integral pump units restrict
coolant flow of inlet by valving or other means to check cutoff point
against design cutoff temperature. Reset control and start the heater,
operate until automatic cutoff occurs again. On the first trial with
slow temperature buildup, inability to initiate cutoff within 5 F of the
temperature specified in 3.8.4.2(e) sahll constitute failure of the test.
On the second trial with blocked coolant circulation, temperature criteria
shall not apply, but inability to cut off end purge without coolant
blowoff, hammering, or other evidence of excessive coolant temperature
shall constitute failure of that test.
4.5.4.7 Motor overheat. This test shall be applied to the pump and
blower motors. Place the motor in a small test cell with electric leads.
connected and brought out so that a circuit continuity check can be made.
Raise the temperature in the test cell slowly while circuit continuity
is checked frequently. Record the temperature at which the overheat
control opens the circuit and compare with the motor manufactures design
data - Also disassemble and inspect the motor for evidence of damage
to the windings and other components. A difference of more than 10- F
from the designer's cutoff point or damage to the motor shall constitute
failure of this test.
4.5.4.8 Circuit breaker.
4.5.4.8.1 Starting current. Rig the blower motor and coolant pump
motor to block their rotors from turning. Connect the heater to a
power source which can maintain at least 22 volts under the current draw
20
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