MIL-PRF-13312R
following exceptions to verify that the capacity of the refrigeration unit is not less than 18,000 Btu/hr.
a. In 4.3.2.3.2 (b), the thermocouples shall be installed as specified. However, the temperature
difference between the air entering the evaporator and leaving the evaporator section shall not be
recorded.
b. In 4.3.2.3.2 (f), sufficient heat shall be added to maintain 350 F + 10F temperature of air
entering the evaporator in place of 00F temperature specified.
c. In 4.3.2.3.2 (g) 2, temperature of the air entering the evaporator has been maintained at
35 F + 10F in place of 00F temperature specified.
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4.3.2.4 Defrost test. With the refrigeration unit operating in a maximum ambient temperature of
32 F and the insulated structure maintained at 00 F + 100F, the evaporator shall be frosted up by
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spraying water on the coil surface or evaporating water in the box. After the coil is frosted, the
refrigeration unit shall be set on the defrost cycle and the condensate collected and weighed.
Verification shall be made that the unit operates through a complete defrost cycle, that no less than 10
pounds of condensate is produced in 30 minutes, that no overloading of the compressor motor or diesel
engine occurs, that there is no damage to the compressor because of lack of lubrication or refrigerant
"slugging" and that no condensate gets into the food storage area.
4.3.2.5 Design reliability test. A 2500-hour design reliability test shall be run as follows:
a. A maximum of two units shall be used for this test. When two units are used, each unit shall
be tested for a minimum of 1000 hours and their combined testing time must equal 2500 hours.
b. The refrigeration unit shall be clamped to the evaporator opening of the calorimeter (see
4.3.2.3.1) with a minimum volume of 150 cubic feet.
c. A combined heat load of approximately 7000 Btu/hr shall be imposed on the unit so the
compressor will cycle with running time of approximately 75 percent when the condenser air entering
temperature is 1100F.
d. The air entering the condenser and surrounding the condensing section shall be maintained at a
minimum of 1100F for 2250 hours of operation, and at a minimum of 1250 F for 250 hours of operation.
Operating hours for the units shall be the hours the compressor is operating.
e. The defrost control shall be set for two defrosts in a 24-hour period of operating time.
f. The refrigeration unit shall be operated with the thermostat set at 00 F for 36 hours and at
400 F for the next 36 hours. This cycle shall be repeated until the 2500 operating hours have been
completed. During the test, suction and discharge pressures, air temperature entering the condenser,
refrigerated enclosure temperature, and compressor operating hours shall be recorded every hour on
automated recording instruments.
g. Failure of the unit to maintain the temperature of the enclosure, failure to start and operate,
failure to defrost, or any mechanical or control failure that requires more than 30 minutes to repair,
shall be defined as a unit failure. A malfunction that can be repaired in less than 30 minutes shall be
classified as an incident.
h. When failure to complete test hours occurs, the failure shall be analyzed, correction made, and
the test started from time zero. All failures, analyses, and corrective actions shall be recorded.
i. The test shall be successfully completed when the unit has completed 2500 hours without
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