-------Internal training document for Haier service provider. External disclosure is prohibited --- Classification
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8. Case Prevention Measures, Product Use and Daily Maintenance
Knowledge
8.1 Refrigeration Principle of ULT Freezer:
The ultra-low temperature freezer is equipped with a cascade refrigerating system normally composing
of two or more refrigerating systems, i.e. low temperature stage and high temperature stage. For the
high temperature stage, the medium-temperature refrigerant is used; for the low temperature stage, the
low-temperature refrigerant is used. Each part is a complete refrigerating system, a cooling evaporator is
used for linking the two parts together, and it is an evaporator of not only the high temperature stage but
also the low temperature stage. The low temperature refrigerant absorbs heat from the cooled object in
the evaporator of the low temperature system and then transfers the heat to the refrigerant in the high
temperature system through the cooling evaporator, and then the refrigerant in the high temperature
system transfers heat to the cooling medium in the high temperature condenser.
8.2 ULT Freezer Use Method
Use Method:
After the ULT freezer is used for the 1
st
time or moved or switched off (including power failure) over 10h,
check it before being used again (or switched on again). Check and test if it is qualified.
Low temperature freezer use method:
1) The freezer shall be switched on only after it is unmoved for 24h.
2) Keep the freezer empty and switch it on. Firstly, reduce the temperature of the freezer to -40
℃
by stage. After the freezer is switched on and off normally, reduce its temperature to -60
℃
. 8h
later, reduce its temperature to -80
℃
and observe if the freezer is normal after being switched
on for 24h. If yes, prove if the freezer is normal.
3) After confirming the freezer is normal according to operation steps in part 2), you can put goods
into the freezer. In principle, goods to be stored at -60
℃
shall not exceed 1/3 of the container
capacity.
4) Taboos: All low temperature preservation containers shall be low temperature preservation
equipment and used for preserving low temperature goods but not for quick-freezing high
temperature plasma products. It is strictly forbidden to put too many relatively hot goods into the
freezer. Otherwise, the compressor will run continuously for a long time and might burn easily
and goods in the freezer might be damaged if the temperature does not go down constantly.
Goods shall be put into the freezer in batches and the temperature shall be reduced step by step,
until it reaches the low temperature you need!!!
8.3 Working Principle of Pressure Switch
A. Principle: When the pressure in the pressure switch pipe exceeds 2.1MPa, the contact is
disconnected, the low temperature freezer switches off and the pressure goes down. When the pressure
drops to 1.35MPa, the contact is connected and the low temperature freezer switches on. When the
pressure exceeds 2.1MPa, the contact is disconnected again and the circulation starts sequentially.
B. Notes: When the pressure switch is burnt, put a wet towel on it and keep the temperature no more
than 100
℃
. Parameters of this pressure switch are not adjustable.
C. Parameters: 220V, 50Hz, contact capacity: 6A.
8.4 Refrigerant Characteristics
1). Refrigerants are mixed and some of them are combustible and explosive. The charging place shall
be ventilated. In case of leakage, it is forbidden to ignite or spark nearby. In case of any failure of the
refrigerating system, the local after-sales service provider will analyze and feed it back and the engineer
of Medical Business Division of Haier will give an instruction to the local after-sales service provider on
maintenance according to the actual condition.
2) Refrigerant Code (Regular): high temperature stage: R134a and R404a; low temperature stage: R290
and R508b.
(Energy-saving): high temperature stage: R290; low temperature stage: R290 and R170.
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