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Main Parts of Truck Refrigeration Unit

May 25,2021

Main Parts of Truck Refrigeration Unit

- A complete truck refrigeration unit system mainly consists of the condenser & evaporator coils, compressor, expansion valve, oil separator, reservior, filter drier, fans, solenoid valves, electric control system, pressure switches, hose pipes and fittings and so on.


1. Compressor

It is a driven fluid machine that elevates low-pressure gas to high-pressure gas, and is the heart of the truck refrigeration unit. It sucks in low-temperature and low-pressure refrigerant gas from the suction pipe, and through the operation of motor or the engine drives the piston to compress it, high temperature and high pressure refrigerant gas is discharged from exhaust pipe to provide power for the refrigeration cycle, and achieve compression→condensation ( Heat release) → expansion → evaporation (heat absorption) refrigeration cycle.

2. Parallel flow condenser coil

Parallel flow heat exchanger is a kind of micro-channel radiator that dissipates heat outwards. It is mostly made of aluminum and combined with forced air cooling from fans. Its features are compact structure, light weight, low refrigerant charge, high heat exchange, and current Widely used in home air conditioners, automobile air conditioners, truck refrigeration units, commercial home refrigeration units and other industries.

3. Copper tubes and fins evaporator coils

The tube-fin heat exchanger is the most widely used heat exchange equipment in gas-gas and gas-liquid heat exchangers. It achieves the purpose of enhancing heat transfer by adding fins to ordinary light tubes. The materials are: Copper tubes, aluminum tubes, stainless steel tubes, etc. The fins are made of copper, aluminum, stainless steel, etc. Our industry mostly uses copper tubes and aluminum sheets, which are matched with forced air cooling by fans. The feature is that the structure is strong, reliable, adaptable, and easy to manufacture, an they can withstand higher operating pressure and temperature.

4. Expansion Valve

The expansion valve is an important part in the refrigeration system, and is generally installed between the liquid reservoir and the evaporator. The expansion valve causes the medium temperature and high pressure liquid refrigerant to become low temperature and low pressure wet vapor through its throttling, and then the refrigerant absorbs heat in the evaporator to achieve the cooling effect. The expansion valve controls the valve flow rate through the change of the superheat at the end of the evaporator, to prevent underutilization of evaporator area and compressor liquid hammer phenomenon.

5. Reservoir

The reservoir is installed between the condenser and the expansion valve and with following functions:

A: Temporarily store the liquid refrigerant flowing out from the condenser, so that when the refrigeration load changes and there is a slight leakage in the system, the amount of liquid refrigerant supplied to the expansion valve can be supplemented and adjusted in time to ensure the continuity and stability of the refrigerant flow.

B: It can prevent too much liquid refrigerant from being stored in the condenser, so that the heat transfer area of the condenser is reduced and the heat dissipation efficiency is reduced.

C: It can filter out the impurities in the refrigerant gas and absorb the moisture to prevent the refrigerant pipes from being clogged and ice jams, and protect the equipment components from corrosion, so as to ensure the normal operation of the refrigeration system.

D: The reservoir with a sight glass can observe the flow state of the refrigerant gas during work, so that it can be judged whether the amount of refrigerant is appropriate.

E: There is a safety fuse to install on the outlet ends, which will melt when the pressure and temperature is too high, so as to ensure the safety of components. It is a safety protection device for the refrigeration system.

6. Oil separator

When the high-pressure gas discharged from the compressor enters the oil separator, because the passage area suddenly increases, the gas flow rate suddenly decreases, the flow direction also changes (the wall of the oil separator rotates at a high speed), and the filter inside the oil separator is blocked, so the gas The entrained oil vapor and oil droplets are separated from the gas due to their high specific gravity and accumulate at the bottom of the container. Only a very small amount is mixed in the gas and carried to the condenser and evaporator. The end of the bottom capillary goes deep into the bottom of the oil, and the oil is discharged after the capillary is cooled and pressured, thereby realizing the oil and gas separation in the whole process.

7. Filter Drier

1. There are filter cotton and metal filter at the outlet end, which can effectively filter impurities.

2. It is equipped with molecular sieve with excellent moisture absorption characteristics as a desiccant to absorb the moisture in the refrigerant to ensure the smooth flow of the capillary tube and the normal operation of the refrigeration system. When the desiccant fails due to excessive water absorption, it should be replaced in time.

8. Solenoid valve

Defrost solenoid valve:

The defrost solenoid valve is located on the defrost pipe. It is a normally closed valve that controls the defrost process. When it is not energized during normal cooling, it cannot be turned on. If it enters the defrost mode, the defrost valve will be energized, and the inlet and outlet pipelines will be connected.

Liquid supply solenoid valve:

The liquid supply solenoid valve is located on the liquid supply pipe. It is a normally open valve that controls the refrigeration process. It is not energized during normal refrigeration, that is, the inlet and outlet are connected. If it enters the defrost mode, the liquid supply valve will be energized, and the inlet and outlet will be cut off.

9. Fans (Evaporator fan/condenser fan)

It is an auxiliary electronic component of the system. It is the forced convection of the air inlet and outlet of the coils to accelerate the heat absorption of the evaporator and heat dissipation and cooling of the condenser. It is an axial flow fan. The control method is simple. Ratio is the highest.

10. High pressure pressure switch and low pressure pressure switch

The high pressure switch opens when the system pressure is higher than the upper limit, and the controller alarms and shuts down to prevent the system pressure from being too high, resulting in the risk of system leakage;

The low pressure switch is opened when the system pressure is lower than the allowable lower limit, and the controller alarms and shuts down to prevent the risk of damage to the compressor due to low system pressure.

11. Control panel

It is the core of the entire electronic control system. The summary, judgment, identification, and issuing of control commands of all information are realized by the controller, which can display return air temperature, defrost temperature, operating time, setting temperature, fault information, etc. , Can operate in cooling, defrosting, heating and other modes.

12. Electric control box

It is the relay unit in the system. The controller sends the start-stop control signal of the electric device, and controls the on-off between the evaporator fan, condensing fan, compressor, solenoid valve and other electrical devices and the main power supply through the relay in the electric control box. So as to realize the start and stop of electrical devices. It is a mode that uses a small current to control a large current. The signal lines are all mA level, and the electrical appliances to be controlled have currents ranging from a few amperes to more than 20 amperes.

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