First, the compressor return air frosting
Frost on the compressor return air port indicates that the temperature of the compressor return gas is too low, so what will cause the temperature of the compressor return gas to be too low?
It is known that if the volume and pressure of the refrigerant of the same quality are changed, the temperature will behave differently. That is, if the liquid refrigerant absorbs more heat, then the refrigerant of the same quality will exhibit high pressure, temperature and volume. Less endothermic pressure means lower pressure, temperature and volume.

That is to say, if the return air temperature of the compressor is low, it will generally show that the return air pressure is low and the amount of refrigerant of the same volume is high. The root cause of this situation is that the refrigerant flowing through the evaporator cannot completely absorb itself and expand to a predetermined level. The heat required for the pressure and temperature value causes the temperature and pressure volume value of the return air to be relatively low.

There are two causes of this problem:

1. Throttle valve supply of liquid refrigerant is normal but the evaporator cannot absorb heat and supply refrigerant to expand normally.

2. The evaporator absorbs heat normally, but the throttle valve has too much refrigerant supply, which means too much refrigerant flow. We usually understand that there is too much fluorine, which means that too much fluorine will cause low pressure.

Frost frost on the compressor due to lack of fluorine

1. Due to the extremely small flow of refrigerant, the first expandable space will begin to expand after the refrigerant flows out of the rear end of the throttle valve. Most of us see that frost on the liquid separation head at the rear end of the expansion valve is often due to lack of fluorine or expansion valve. Caused by insufficient flow. Too little refrigerant expansion will not make use of the entire evaporator area. It will only form a low temperature in the evaporator. In some areas, the rapid expansion due to the small amount of refrigerant will cause the local temperature to be too low, and the evaporator will frost. .

After local frosting, due to the formation of a heat insulation layer on the surface of the evaporator and the low heat exchange capacity in this area, the refrigerant expansion will be transferred to other areas. Frost or icing of the entire evaporator gradually occurs, and the entire evaporator forms heat insulation. Layer, so the expansion will spread to the compressor return pipe and cause the compressor return air to frost.

2. Due to the small amount of refrigerant, the low evaporation temperature caused by the low evaporation pressure of the evaporator will also gradually cause the condensation of the evaporator to form a heat insulation layer, and the expansion point will be transferred to the return air of the compressor, causing the return air of the compressor to frost. The above two points will show the evaporator frost before the compressor returns to frost.

In fact, in most cases, for the frost connection phenomenon, as long as the hot gas bypass valve is adjusted, if there is no hot gas bypass valve, if the frost phenomenon is severe, the take-off pressure of the condensation fan pressure switch can be appropriately increased.

The specific method is to find the pressure switch first, remove the adjusting nut of the pressure switch to fix the small piece, and then use a Phillips screwdriver to rotate clockwise. The entire adjustment also needs to be performed slowly. Adjust it a half circle to see if the situation requires adjustment.

3. Frost on the cylinder head (frost frost on the crankcase in severe cases)

Frost on the cylinder head is caused by a large amount of wet steam or refrigerant being sucked into the compressor. The main reasons for this are:

1. The opening degree of the thermal expansion valve is adjusted too large, the temperature sensor package is incorrectly installed or loosened, so that the temperature felt is too high, which causes the valve core to open abnormally.

Thermal expansion valve is a direct-acting proportional regulator that uses the superheat degree at the outlet of the evaporator as a feedback signal, and compares it with a given superheat value to generate a deviation signal to regulate the refrigerant flow into the evaporator. Encoder, regulator and actuator in one.
When the measured parameter of the transmitter is deviated from the given value, the physical quantity of the transmitter changes and generates enough energy to directly push the actuator to move. The position of the actuator changes in proportion to the adjusted parameter. According to different balance methods, thermal expansion valves can be divided into two types: internal balance type thermal expansion valve and external balance type thermal expansion valve.

The liquid refrigerant absorbs heat in the evaporator, and when it reaches the outlet of the evaporator, it has completely vaporized and has a certain degree of superheat. The thermal expansion valve of the thermal expansion valve is closely attached to the outlet pipe of the evaporator, and the temperature at the outlet of the evaporator is sensed. If the liquid in the warm pack is the same as the refrigerant, the pressure of the liquid above the diaphragm of the thermal expansion valve is greater than the pressure of the liquid below the diaphragm, and the higher the temperature of the evaporator outlet, that is, the greater the degree of superheat, the The greater the liquid pressure.
This pressure difference is balanced by the tension of the adjusting spring under the diaphragm through the ejector pin. If the tension of the adjusting spring is changed, the upper force of the ejector rod can be changed, thereby changing the opening degree of the needle valve. Obviously, the degree of overheating of the evaporator will also cause the change of the needle valve opening. When the adjustment spring is adjusted to a certain position, the expansion valve will automatically change the needle valve opening according to the temperature of the evaporator outlet, so that the superheat of the evaporator outlet is maintained at a certain value.

The opening degree of the thermal expansion valve is adjusted too large, the temperature sensor package is installed incorrectly or loosened, so that the perceived temperature is too high and the valve core is opened abnormally, so that a large amount of wet steam is drawn into the compressor and the cylinder head is frosted. The thermal expansion valve is used in conjunction with the adjustment of the superheat degree when the evaporator works.

The overheating degree of the evaporator outlet is too long, the overheating section at the rear of the evaporator is too long, and the cooling capacity will be significantly reduced; the overheating degree of the outlet is too small, which may cause the compressor to hit or even frost the cylinder head. It is generally considered that it is appropriate to adjust the expansion valve to work at an evaporator outlet with a superheat degree of 3 ° C to 8 ° C.

2. The expansion valve is not tightly closed when the liquid supply solenoid valve leaks or stops, causing a large amount of refrigerant liquid to accumulate in the evaporator before starting. The temperature relay is used in combination with a solenoid valve for control.

The temperature sensing package of the temperature relay is placed in the cold storage. When the temperature of the cold storage is higher than the upper limit of the set value, the temperature relay contacts are turned on, the solenoid valve coil is energized, the valve is opened, and the refrigerant enters the evaporator to cool down. At the lower limit of its setting value, the temperature relay contact is opened, the solenoid valve coil current is cut off, the solenoid valve is closed, and the refrigerant stops entering the evaporator, so that the storage temperature can be controlled within the required range.

3. When there is too much refrigerant in the system, the liquid level in the condenser is high, the condensing heat exchange area is reduced, and the condensing pressure is increased, that is, the pressure in front of the expansion valve is increased, and the amount of refrigerant flowing into the evaporator is increased. The agent cannot be completely evaporated in the evaporator, so the compressor sucks wet steam, the cylinder hair is cold or even frost, and it may cause "liquid strike", and the evaporation pressure will be too high.