Why does the air conditioner evaporator get frost?

The frosting of the evaporator of the air conditioner is a relatively common phenomenon in the refrigeration industry, and it is also a technical problem that has received more attention. Today, let's take a look at why the air conditioner evaporator is frosted and how to solve this frosting problem?

, 8 basic reasons why the evaporator will frost To sum up, there may be the following 8 reasons:

① Insufficient supply of air volume, including blockage of outlet and return air duct, blockage of filter screen, blockage of fin gap, non-rotating fan or reduced speed, etc., resulting in insufficient heat exchange and reduced evaporation pressure , the evaporating temperature is reduced;

②The problem of the heat exchanger itself, the heat exchanger is commonly used, the heat exchange performance is reduced, and the evaporation pressure is reduced; Lower cooling will cause insufficient heat exchange and low evaporation pressure;

④ The expansion valve is damaged by the plug or the pulse motor system that controls the opening. In the long-running system, some sundries will block the expansion valve port, making it unable to work normally, reducing the Refrigerant flow, the evaporation pressure is reduced, and the abnormal opening control will also cause the flow to decrease and the pressure to decrease; The pressure and temperature drop in the part after the flow;

⑥The system is not well matched, to be precise, the evaporator is small or the working condition of the compressor is too high. In this case, even if the performance of the evaporator is fully exerted, due to the compression Excessive working conditions will cause low suction pressure and evaporating temperature;

⑦Lack of refrigerant, low evaporating pressure and low evaporating temperature;

⑧Too much refrigerant, many people think that too much refrigerant will not cause frost, but refrigerant After too much, the excess refrigerant is basically stored in the liquid state in the pipeline from the rear section of the condenser to the expansion valve. At this time, the system circulation becomes slower, the supercooling degree of the liquid refrigerant increases, and the opening of the expansion valve decreases. The evaporating temperature is reduced, and I have seen too much refrigerant and the temperature of the return pipe is negative.

However, for these 8 reasons, we cannot talk about them in general terms, and the specifics also depend on the actual situation:

Both low evaporation temperature and insufficient heat exchange are indispensable, so ①-③ can cause frosting of the evaporator alone , and ④-⑧ only causes low evaporation. If the external conditions of heat exchange are good enough, it is difficult to form frost. Take ⑦ as an example, if the lack of refrigerant causes the evaporation temperature to drop to -3℃, but if my The cooling condition is 27/19 ℃ in summer, the air volume is sufficient, the performance of the heat exchanger is good, and there will be no frosting phenomenon.

What needs to be added is: the evaporation temperature mentioned in refers to the evaporation temperature when there is liquid gasification. When the refrigerant completely becomes gaseous, with the heat exchange of and , the gaseous refrigerant will be overheated, so it is generally evaporated Frost on the evaporator will cause partial frost, especially when the air volume, external temperature and heat exchanger performance are good at ④⑤⑦, ④ and ⑦, it will only cause frost on the outlet of the expansion valve and the front section of the evaporator (the frost layer deteriorates heat transfer). performance, there are cases where the rear section is also frosted), ⑤ will cause the evaporator after the secondary throttling to frost.

According to this, I personally think that the cause of the heat exchanger frosting is ①②③＞⑥⑧＞④⑤⑦. Of course, the evaporator frosting is mostly the result of the combined effect of the above factors.

Let's talk about the frosting of the return air pipe: The return air pipe is different from the heat exchanger in that it does not have forced convection heat exchange of air, so it is easy to frost when the temperature is lower than zero. Therefore, except for ④ and ⑦, it is possible to cause frosting of the return trachea, among which the possibility of secondary throttling is relatively large. Personally, I think the primary and secondary order is ⑤>①②③>⑥⑧.

Here, what I want to say is:

Specific analysis of specific problems!

The most important thing is to be careful! thin! Look!

For example, look at the frosting direction...

, the frosting direction is different, and the reason for the judgment is different

Basically, if the evaporator is frosted, it basically starts from the following two directions.

. The reason for the frost forming gradually from the compressor return port to the evaporator direction:

(1) The opening of the throttle valve is too large. The air port begins to gradually form frost in the direction of the evaporator.

(2) The evaporator cannot absorb heat normally, or the cold energy generated by the evaporator cannot be taken away. The appearance is that the temperature and pressure of the return liquid are normal or slightly low. Frost starts to gradually form from the compressor's return port to the evaporator. After a long time, all the ice forms from the compressor's return port to the evaporator and from the throttle valve to the evaporator. , and finally a low pressure.

The inspection method is:

· Check whether the air filter is clean;
· Check whether the fan speed is normal;
· Whether the evaporator is clean;
· Whether the air supply system is blocked; Possible reasons for frosting in the direction of the evaporator

(1) There is less refrigerant (leakage), the appearance is that the return liquid temperature of the condenser is high but the pressure is not high, and frost gradually begins to form in the direction of the evaporator from the throttle valve.

(2) The opening of the expansion valve is too small, and the appearance is that the temperature and pressure of the condensate return liquid are normal or slightly low, and frost gradually begins to form toward the evaporator from the throttle valve.
(3) Check the sight glass to see the refrigerant condition, if the bubbling is serious, it may be a system leak; if the refrigerant in the sight glass does not bubble or rarely bubbles, it may be that the expansion valve is opened too small, or Blockage, generally there will be a large temperature difference before and after the blockage.

当然

除了看结霜方向

如果蒸发器翅片表面都结霜了

那还得做更细致一步的分析……

蒸发器结霜原因再细化

蒸发器翅片表面结霜，结The evaporator temperature in the frost part is lower than 0°C, and the frost formation speed is related to the ambient temperature and humidity. Evaporator frosting has two phenomena:

(1) One phenomenon is that frost starts from the outlet of the evaporator.

over time covered the entire evaporator surface. This phenomenon may be caused by excessive liquid supply for the evaporator (the capillary system has an obvious response), and may be a problem with the return air system and control system for the entire refrigeration system of the household air conditioner:

a. Return air filter Dust blockage, dust blockage on the surface of the evaporator fins, bad or small capacitance of the fan, non-rotating fan motor, slow speed and other reasons, cause the heat exchange load of the evaporator to be reduced.
b. Refrigeration operation under the condition of low ambient temperature or long-term refrigeration operation under the condition that the resistance of the return air temperature sensor changes.In the household air conditioner , if the control system has anti-freeze protection function, after the refrigeration system runs for a period of time, when the control system detects that the temperature of the evaporator coil is lower than 0 ℃, the controller automatically shuts down the compressor and outdoor fan For protection, the indoor fan runs with high-speed wind. During the protection period, when the temperature of the indoor evaporator coil is greater than 10°C, the protection will be cancelled and the cooling will be resumed. If it is found that the frost on the surface of the evaporator does not disappear for a long time, the evaporator coil sensor and return air temperature sensor of the control system may be faulty or the control system has no anti-freeze protection function.
c. Some air conditioners have a continuous operation function. When the continuous operation function is turned on, the operation of the refrigeration system is not controlled by the temperature of the temperature sensor , and the surface of the evaporator will be frosted after a long operation time. Just turn off the continuous operation function. During maintenance, first check the evaporator fins, fan system, controller return air temperature and coil temperature sensor, and the ambient temperature at the time of operation, and confirm that there are no problems with the inspected components before judging whether the system has a large amount of fluorine injected. The high fluorine content rate is generally a phenomenon that may occur after the system is refilled with refrigerant. Here is a point to explain, the fluorine content of the system is more likely to operate under the condition of high ambient temperature without frost on the surface of the evaporator, and when the ambient temperature is low, frost may occur on the surface of the evaporator.

(2) Another phenomenon is that it starts to bloom after capillary throttling.

With the passage of time, the surface of the evaporator is seriously frosted, and most of the surface of the evaporator has no condensation. This phenomenon is a manifestation of insufficient liquid supply to the evaporator of the refrigeration system. For the entire refrigeration system of the household air conditioner, it may be that the system has a leak or the throttling system is half-blocked. Distinguish whether the system is leaking or the throttling system is half-blocked:

a. The outlet air temperature of the condenser is high, the current is large, and there is some frost at the inlet of the evaporator, which is not cooling, mostly because the throttling system is half-blocked. The filter before the inlet of the capillary at the fault location is dirty and blocked, or the indoor and external connecting liquid pipes (thin tubes) are flattened to form a secondary throttling.
b. The outlet air temperature of the condenser is not high, the current is small, and there is some frost at the inlet of the evaporator, which is not cooling, most of which are leaks in the refrigeration system pipeline. The system pipelines, welding points, interface pockets, valve cores, valve caps, especially the parts with oil stains in the system pipelines at the fault location. There should be a system capability protection function in the household air conditioner control system. In the cooling mode, after the compressor runs continuously for 30 minutes, the temperature of the indoor evaporator coil is ≥25°C (some manufacturers use the indoor ambient temperature - the temperature of the indoor coil is ≤4°C), stop the compressor, outdoor fan, indoor fan Run at the set wind speed. Entry protection generally requires a power outage to exit. Some control systems have no protection function, and the compressor may overheat protection when the compressor runs continuously.