There is a peculiar smell in the car air conditioner when the heater is on - what is the reason?

Question:

Winter has officially arrived, and it has already snowed in many places. It is necessary to turn on the heater when driving a car; however, many vehicles will smell strange smells when using the heater. Where do these smells come from, and how can they be solved?

It is very normal for the car air conditioning system to have odor. As long as the heating and cooling air conditioners are used throughout the year, the odor will inevitably appear when the heater is used. The reason is actually very simple. The first thing you need to understand is the knowledge of "air conditioning water". Careful drivers will always find this problem. When using the cold air conditioner at idle speed, a lot of water will flow out from the front of the chassis. This is air conditioner condensation water.

Basic knowledge

The principle of automobile air conditioning and refrigeration seems complicated but is actually very simple. In short, it is two "heat conductions".

The refrigerant absorbs the heat energy of the evaporation box and cools it down

The evaporation box absorbs the heat energy of the hot air and cools it down

After completing these two steps, cold air will be generated, so-called The cold air is actually the air that has been absorbed by the evaporation box; and the condensed water also comes from this air, because the higher the temperature of the air, the stronger its ability to carry water molecules, or it can be understood as the greater the humidity - when water vapor is cold, It will condense into liquid water. After the evaporation box absorbs heat energy from the refrigerant and is cooled down, it reaches the ideal standard for condensing water vapor, so a large amount of condensed water will appear.

Figure 1: Refrigerant cycle process. The condenser cools the refrigerant. After passing through the collision valve, the gaseous tetrafluoroethane (refrigerant) will become liquid; and the boiling point of this refrigerant is lower than At minus 28°C, it will instantly boil and absorb heat in the evaporation box above zero.

Figure 2: Dynamic demonstration

Figure 3: Structure of the evaporation box (focus on the drain outlet)

Explanation: The air humidity inside the evaporation box will be very high , even if there are drainage holes; so low-temperature air will be sent into the car in a "high humidity" state, at least in the air-conditioning pipeline, a humid environment will be formed.

A humid environment is the best environment for mature mold. Of course, the results can be imagined, but it will also exceed the imagination of ordinary car users; because the number of mold spores inside the evaporator box and pipes can reach every There are more than 1,000 molds per square centimeter, which is about the size of a small fingernail.

The key point is that these molds will also "metabolize", and when the mold rots, there will be a peculiar smell; usually it is fishy, ​​earthy or sour smell, and there will be different "odors" in different degrees. .

But at this time, some people are wondering, why is the smell not obvious during the humid stage in the pipeline in summer? In fact, the answer is very simple, because when the air conditioning system is turned on, the temperature is continuously reduced.

The movement speed and intensity of molecules will be affected by temperature. For example, the tire pressure of long-distance driving will increase. The reason is that the high temperature generated by friction will increase the intensity of the movement of air molecules. On the contrary, low temperature will reduce tire pressure. In the same way, low temperature will also reduce the movement intensity of molecules with odor, which is why you are not very sensitive to odors. At the same time, when the temperature drops, the air pressure will increase. If the "air pressure difference" between the lung pressure and the atmospheric pressure is reasonable, breathing will feel natural. High-temperature air will increase the air pressure difference, and the intensity and sensitivity of breathing will be enhanced.

High-temperature odor·Solution

There is no need to go into details about the reasons why the odor appears and is serious. In short, high temperature strengthens molecular movement, and the smell will enter the car more obviously. Inside. But have you noticed another phenomenon, that is, as the time of using the car increases, the intensity of the odor of the warm air will gradually decrease.

Many people think that this is difficult to detect after getting used to it slowly. In fact, this is a wrong understanding; the main reason is that the continuous use of heating air conditioners uses the internal temperature of the pipes heated by the high-temperature water tank to kill mold. To kill. At the same time, a dry environment is not conducive to the growth of mold. The heating air conditioning system does not produce condensation water, because the low-temperature air outside has low humidity. After passing through the high-temperature heating water tank, even some water vapor will be dried, so mold There will be less and less.

Low-cost solution: use the heating system itself to purify! The car's warm air is a "water heating system", and the heat energy comes from the engine's antifreeze coolant.

The antifreeze temperature in a hot car state can reach over 90°C, which is only the standard for idling; if you drive continuously, the water temperature can reach as high as about 110°C. The temperature of the water tank will naturally be equivalent to the antifreeze, otherwise it will not be able to "hot" the cold air in a short period of time (actually, the low-temperature air absorbs the heat energy of the high-temperature water tank and heats up).

Then the air temperature inside the pipeline will naturally be very high. When the car is hot, raise the air conditioner temperature to the highest level and turn on the air volume to the maximum; the standard of warm air is close to killing mold. Level. At this time, open the door and sunroof, run at idle speed for about half an hour, and then clean the interior and seats; when you use the heater and air conditioner again, you will always find that the odor is completely (or basically) gone.

This is the way to clean up the odor of air conditioners. Compared with using cleaning agents, the effect is not bad, and the cost is much lower; the point is that it can be cleaned in this way every year when the cold and hot alternate. The cleaning agent can only last for one winter. Use in summer is nothing more than the smell of the cleaning agent itself covering up the odor.

This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.