What are the faults in the abnormal suction and exhaust temperature of the compressor?

- Apr 12, 2019-

What are the faults in the abnormal suction and exhaust temperature of the compressor?


First, the inhalation temperature is too high



The inspiratory temperature is too high - mainly due to the increased suction superheat. Note that high inspiratory temperature does not mean that the inspiratory pressure is high because inhalation is superheated steam.



Under normal circumstances, the cylinder head of the compressor should be half cold and half hot. If the intake temperature is too high, the cylinder head will heat up. If the inhalation temperature is higher than the normal value, the exhaust gas temperature will increase accordingly.


The main reasons for the high inspiratory temperature are:



(1) Insufficient refrigerant charge in the system: Even if the expansion valve is opened to the maximum, there will be no change in the liquid supply amount, so that the refrigerant vapor is superheated in the evaporator to raise the suction temperature.


(2) The opening degree of the expansion valve is too small: the circulation amount of the refrigerant of the system is insufficient, the refrigerant amount of the evaporator is small, the degree of superheat is large, and the intake temperature is high.


(3) Plugging of the expansion valve port filter: The amount of liquid supply in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the intake air temperature is increased.


(4) Other reasons cause the inspiratory temperature to be too high: if the return air pipe is not well insulated or the pipe is too long, the inhalation temperature may be too high.


Second, the inhalation temperature is too low



The inhalation temperature is too low - mainly due to the high liquid supply of the evaporator resulting in low suction superheat.


(1) Too much refrigerant charge: occupying a part of the volume inside the condenser to increase the condensing pressure, and the amount of liquid entering the evaporator increases. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. Thus, the temperature of the return air duct drops, but the evaporating temperature does not change because the pressure does not decrease, and the degree of superheat decreases. Even if the small expansion valve is closed, there is no significant improvement.


(2) The opening degree of the expansion valve is too large: because the temperature sensing element is loosely tied, the contact area with the return air pipe is small, or the temperature sensing element is not wrapped with the heat insulating material and the wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate. Close to the ambient temperature, the opening degree of the expansion valve action is increased, resulting in excessive liquid supply.


Third, the exhaust temperature is not normal


Exhaust gas temperature is not normal - influencing factors: adiabatic index, compression ratio, inhalation temperature.


The compressor discharge temperature can be read from a thermometer on the exhaust line. It is related to the adiabatic index of the refrigerant, the compression ratio (condensation pressure/evaporation pressure), and the suction temperature. The higher the inspiratory temperature, the higher the compression ratio and the higher the exhaust temperature, and vice versa.


The suction pressure is constant, and the exhaust gas temperature rises when the exhaust pressure increases; if the exhaust pressure does not change, the exhaust gas temperature also rises when the suction pressure decreases. Both of these cases are caused by an increase in the compression ratio. Excessive condensing temperatures and exhaust temperatures are detrimental to the operation of the compressor and should be prevented. Excessively high exhaust temperatures can cause the lubricating oil to become thinner or even charred and coke, which deteriorates the lubrication conditions of the compressor.


The temperature of the exhaust gas is proportional to the compression ratio (condensation pressure / evaporation pressure) and the suction temperature. If the inhalation temperature of the inhalation is high and the compression ratio is large, the exhaust gas temperature is also high. If the suction pressure and temperature do not change, the exhaust gas temperature also rises as the exhaust pressure increases.


The main reasons for the increase in exhaust gas temperature are:

(1) The inhalation temperature is high, and the exhaust gas temperature is higher after the refrigerant vapor is compressed.

(2) The condensing temperature rises and the condensing pressure is high, causing the exhaust gas temperature to rise.

(3) The exhaust valve piece is crushed, the high pressure steam is repeatedly compressed and the temperature rises, the cylinder and the cylinder head are hot, and the thermometer indication value on the exhaust pipe also rises.


The actual factors that affect the rise in exhaust gas temperature are:

If the intermediate cooling efficiency is low, or if the scale in the intercooler affects the heat exchange too much, the inhalation temperature of the latter stage is necessarily high, and the exhaust temperature is also increased.



The gas valve leaks and the piston ring leaks, which not only affects the rise of the exhaust gas temperature, but also changes the interstage pressure. As long as the compression ratio is higher than the normal value, the exhaust gas temperature will rise.

(3) In addition, water-cooled machines, lack of water or insufficient water will increase the temperature of the exhaust. The condensing pressure is abnormal and the exhaust pressure is lowered.


Fourth, the exhaust pressure is higher



The higher the discharge pressure - mainly due to the higher condensing pressure, rather than the press itself.


The discharge pressure generally corresponds to the level of the condensing temperature. Under normal conditions, the compressor discharge pressure is very close to the condensing pressure.


As the condensing pressure increases, the compressor discharge temperature also rises. The compression ratio of the compressor is increased, and the gas transmission coefficient is reduced, so that the refrigeration capacity of the compressor is lowered. The power consumption has increased. If the exhaust gas temperature is too high, the consumption of the compressor lubricating oil is increased, the oil is thinned, and the lubrication is affected; when the exhaust gas temperature is close to the flash point of the compressor oil, part of the lubricating oil is carbonized and accumulated in the suction, The exhaust valve port affects the sealing of the valve.


Reducing the temperature of the cooling medium can cause the condensation temperature to drop and the condensation pressure to decrease, but this is limited by environmental conditions and is difficult to choose. Increasing the flow rate of the cooling medium reduces the condensation temperature (this method is used more often). However, it is not possible to increase the flow of cooling water or air unilaterally, as this will increase the power of the cooling water pump or fan and the motor, and should be comprehensively considered.


High exhaust pressure will increase the compression work and reduce the gas transmission coefficient, thus reducing the cooling efficiency.

The main reasons for this failure:

(1), cooling water (or air) flow is small, high temperature.

(2) There is air in the system to increase the condensing pressure.

(3), the refrigerant charge is too much, the liquid occupies an effective condensation area.

(4), the condenser is in disrepair for a long time, the dirt on the heat transfer surface is serious, and the condensation pressure can also be increased. The presence of scale also has a large effect on the condensing pressure.


Fifth, the exhaust pressure is too low