Do You Master and Understand the Ten Key Temperatures of the Refrigeration System?

The temperatures of the components of the unit all have a normal temperature range. If they exceed this range, it is an abnormal state. The factors causing these abnormalities may be faults or incorrect adjustments. However, the reasons for them need to be analyzed, and timely handling or inspection should be carried out. These temperature points are difficult to measure with a thermometer and can generally only be estimated by touch, and then it can be judged whether they are normal.

I. Discharge Temperature:
Influence of Discharge Temperature: In summer, the discharge temperature of the compressor is relatively high, and it is too hot to touch by hand.
Too High Discharge Temperature: It is caused by an extremely high suction temperature of the compressor or an extremely high condensing temperature, which must be paid attention to.
Too Low Discharge Temperature: When touching the exhaust pipe by hand, it is not hot. This indicates that the suction temperature is particularly low, and the compressor may be operating in a wet stroke or in a state where the system working fluid is quite small. A wet stroke of the compressor can easily damage the valve structure; operating with an extremely small amount of refrigerant will affect the heat dissipation of the motor winding and accelerate the aging of the insulating material.

II. Compressor Shell Temperature:
Influence of the Change of the Shell Temperature on the Compressor and the Refrigeration System. The temperature field on the outer surface of the shell of a hermetic compressor can be divided into two parts:
The upper part of the shell is affected by the suction vapor, and the temperature is relatively low, in the range of slightly warm or a little cool, estimated to be around 30°C. There is a possibility of dew condensation on the local surface of the shell around the suction pipe.
The heat generated by the motor in the lower part of the shell and the frictional heat carried out by the refrigeration oil are mainly carried out of the shell by the vapor.
Influence and Reasons for Too High Shell Temperature: When the surface temperature of the shell exceeds the normal range, it is mainly due to the too high suction temperature (higher than 15°C) of the refrigeration system. When the excessively hot vapor enters the compressor and absorbs the heat inside the shell, the temperature of the vapor becomes even higher, thus increasing the temperature of the shell. When the temperature of the superheated vapor rises significantly, the temperature of the shell also rises high, which is not conducive to the cooling of the oil. This will affect the lubrication of the moving parts, accelerate wear, and in severe cases, the bearing may seize (lock up). In addition, it will also cause the discharge temperature to rise.
Influence and Reasons for Too Low Shell Temperature: When the surface temperature of the shell is lower than the normal range, the reason is that the suction temperature is too low (lower than 15°C). It is beneficial to the cooling of both the refrigeration oil and the motor winding, but the cooling capacity will decrease. When the suction temperature is particularly low, more than half of the shell will be covered with dew, and there is a risk of liquid slugging, which is a fatal blow to the compressor and should be particularly noted. At the same time, a large amount of refrigerant is dissolved in the refrigeration oil, which is not conducive to the lubrication of the moving parts.

III. Condensing Temperature:
Temperature Condition of the Condenser in Normal Situation:
The front half of the heat dissipation tubes is very hot, and the temperature has a tendency to gradually and slowly decrease. The heat sensation of the heat dissipation tubes in the rear half is significantly lower compared to the front half. This is because the refrigerant in the tubes of the rear half has gradually liquefied and has reached the condensing temperature and the subcooling temperature.
When an abnormal situation occurs:
One situation is that the front half is not very hot, and the rear half is close to the ambient temperature.

The reason is that the compressor sucks in wet vapor refrigerant or there is insufficient refrigerant.
The other situation is that the entire condenser tube is very hot, and the reason is that there is too much refrigerant, or the ventilation volume is small, or the ambient temperature is high.

IV. Condenser Shell Temperature:
Water-cooled Condenser:
Under normal circumstances, the upper half of the shell of a shell-and-tube condenser is relatively hot, and the lower half is warm. In an abnormal situation, the entire shell is not very hot, and the reason is insufficient refrigerant.
Another situation is that the entire shell is very hot, and the reason is insufficient cooling water or poor heat dissipation effect (scaling in the water pipe).
Tubular Condenser:
Under normal circumstances, the outer surface of the casing is very hot, and the reason is that the cooling water volume is too small or the heat dissipation effect is poor; in another situation, the outer surface of the entire casing is not very hot, and the reason is insufficient refrigerant.
Air-cooled Condenser:
Under normal circumstances, the upper half of the fins of an air-cooled finned condenser is relatively hot, and the lower half is warm. In an abnormal situation, the entire fins are not very hot, and the reason is insufficient refrigerant.
Another situation is that the fins of the entire condenser are very hot. At this time, you can check whether there is a lot of dust on the outer surface of the air-cooled condenser. If there is too much dust, you can use high-pressure water to flush the fins.

V. Temperature Condition of the Receiver:
Under normal circumstances, the suction pipe feels very cold when touched by hand and is covered with dew. The reason is poor heat dissipation of the condenser, a high condensing temperature, or excessive refrigerant charging.

VI. Temperature Conditions of the Liquid Pipe and the Filter:
Temperature Condition of the Liquid Pipeline: Under normal circumstances, the liquid pipe is warm. In an abnormal situation, the liquid pipe is relatively hot. The reason is poor heat dissipation of the condenser, a high condensing temperature, or excessive refrigerant flow.
Temperature Condition of the Filter: The basic condition is the same as that of the liquid delivery pipe, but there is a prominent abnormal phenomenon, that is, the filter may feel cool. The reason is that the filter mesh holes are blocked by sludge, making the filter unobstructed. When the refrigerant flows through the filter mesh, a throttling phenomenon occurs, that is, part of the liquid vaporizes and absorbs heat, making the filter cool, and in severe cases, there will be dew condensation. Another abnormal phenomenon is that the filter is not hot and is at the same temperature as the ambient temperature. The reason is that the filter mesh is completely blocked and the refrigerant cannot flow.

VII. Temperature Condition of the Suction Pipe: Under normal circumstances, the suction pipe feels very cold when touched by hand and is covered with dew. In an abnormal situation: the suction pipe is colder, and there is too much dew, resulting in a large area of dew condensation on the shell. The suction pipe is not cold, there is no dew condensation, and the shell is very hot. The reason is that the refrigerant flow is too small or there is insufficient refrigerant. The consequence is that the discharge temperature rises and the cooling capacity decreases.

VIII. Temperature of the Thermal Expansion Valve and the Evaporation Temperature: Thermal Expansion Valve (including Electronic Expansion Valve): Under normal circumstances, the lower half of the valve body of the expansion valve is very cold, and there is dew, and the flow sound of the refrigerant is very dull. In an abnormal situation, first, the valve body is relatively cold, there is more dew on the surface, and even frost forms, and the flow sound of the refrigerant is relatively loud (gas flow). The reason is that the filter mesh is blocked, or the refrigerant in the power box leaks, and the valve hole is closed and unobstructed.
Temperature of the Capillary Tube: Under normal circumstances, the capillary tube is cool and covered with dew, and there is a sound of liquid flow. In an abnormal situation, first, the surface is very cool and also has dew, but the flow sound is louder, which is gas flow, and the reason is insufficient refrigerant; second, the surface is not cool, there is no dew, and no flow sound can be heard, and the reason is that the filter mesh or the capillary tube is blocked.
Temperature Condition of the Evaporator: Under normal circumstances, the outer surface of the evaporator is very cold, and the condensed water droplets keep dripping down, and the temperature difference between the inlet and outlet air is large. Usually, Δt can be 12~14°C. In an abnormal situation, the surface of the evaporator is not very cool, there is not much dew, or there is no dew condensation, and a very loud flow sound of the refrigerant can be heard, and the temperature difference between the inlet and outlet air is small. The reason is insufficient refrigerant or a small opening degree of the expansion valve.

IX. Environmental Temperature Requirements for the Outdoor Unit: According to the national standard, when the environmental temperature of the outdoor unit is below 35°C, the air conditioning unit should ensure normal operation and be able to reach the cooling capacity and other various indicators marked on the product nameplate. When the environmental temperature is in the range of 35~43°C, the air conditioning unit can operate, but it cannot guarantee the cooling capacity marked on the nameplate. It is already in full-load operation. At this time, the condensing temperature, pressure, and discharge temperature are quite high. If the heat of the indoor unit is relatively large, the electronic control protector may operate, cut off the power supply, and stop the operation. When the outdoor temperature exceeds 43°C, the air conditioning unit is in overload operation, which will lead to the operation of the electronic control protection device, cut off the power supply, and stop the operation.

X. Requirements for the Indoor Air Temperature of the Air Conditioner: It is better that the highest normal constant indoor temperature should not exceed 30°C. If it operates at a temperature exceeding 30°C, the air conditioning unit may be in an overload working condition. The condensing temperature and the discharge temperature of the refrigeration system will rise, and it may also lead to the operation of the electrical protector, cutting off the power supply, which is not conducive to the service life of the air conditioning unit.
The situation of the heat pump system is the same as that of the single-cooling system. Whether the heat pump operates normally mainly depends on checking the working condition of the four-way reversing valve. When the reversing valve changes direction, a relatively loud gas flow sound and the impact sound of the solenoid valve thimble (the electromagnetic field attracts the valve core) can be heard. When these two sounds cannot be heard during the reversing process of the solenoid valve, the solenoid valve may be faulty.