MIL-PRF-12574M
application of statistical process control, tool control, or cost-
effective sampling procedures to verify performance (see 6.4).
4.3.2 Operating requirements verification .
All operating
requirements shall be verified as follows.
4.3.2.1 4-hour operation test . The refrigeration unit
evaporator shall be clamped to the evaporator opening of a
calorimeter or other insulated structure. All refrigeration unit
components shall be in place and the refrigeration unit doors shall
be closed. The refrigeration unit shall be operated for 4 hours to
determine that all mechanical and electrical components are
functioning as intended and all controls are in calibration. The
units shall have a heat load applied to the enclosure so that the
unit operates more than 50 percent of the test time and cycles on
the automatic controls three or more times per hour. Suction
pressure at the compressor shall be verified to be within the
established guidelines of the compressor manufacturer. Prior to
completion of the 4-hour test, the air flow to the condenser shall
be blocked off and the unit operated and automatic shutdown of the
refrigeration unit verified when compressor discharge limit is
exceeded. During normal operation, the discharge pressure shall be
observed to be not less than that recommended by the compressor
manufacturer for the refrigerant used. The air exiting the
evaporator shall be checked to verify that the airflow direction is
out and upward.
After a minimum operating time of 1 hour with the thermostat
set at 0 0F, the moisture indicator shall be observed to verify that
the moisture content as shown by the component manufacturer's color
chart data is not greater than 25 parts per million. A check for
refrigerant leakage shall also be performed with the unit
inoperative with a leak detector having a maximum sensitivity of
0.40 oz per year. Leakage shall be checked to verify that it is no
greater than 0.5 oz per year, except the compressor shaft seal
leakage is no greater than 3.0 oz per year.
4.3.2.2 72-hour operating test .
A 72-hour test shall be
conducted as follows:
a. The refrigeration unit shall be clamped to the evaporator
opening of a calorimeter or other insulated structure.
b. A combined heat load of 3000 Btu/hr shall be impressed
when the thermostat is set at 0 0F and 4000 Btu/hr when the
thermostat is at the 35 0F setting.
c. The refrigeration unit shall be operated 36 hours with
the thermostat set at 0 0F and 36 hours with the thermostat set at
350F. During this test, suction and discharge pressure, ambient
air, condenser air, and evaporator in and out air temperatures
shall be recorded on automatic recording instruments. Normal
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