Why does the car air conditioner alternate between hot and cold?
3 Answers
Reasons why the car air conditioner alternates between hot and cold include loose wiring of the compressor; poor contact of the pressure switch; poor contact of the relay; and failure of the compressor clutch. Additional information: High-temperature gas cools into liquid: When the air conditioner is first turned on, the compressor starts working, compressing the gaseous refrigerant in the system into a high-temperature and high-pressure gas, which is then sent to the condenser for cooling. After cooling, it becomes a high-temperature and high-pressure liquid, which is then dried and filtered through the dryer bottle, passes through the expansion valve and evaporator, and returns to the compressor. Expansion of high-temperature and high-pressure liquid: When the high-temperature and high-pressure liquid passes through the expansion valve, all the expanded liquid undergoes a drastic change, turning into a low-temperature and low-pressure liquid. This low-temperature and low-pressure liquid causes the temperature of the evaporator to drop rapidly, so the air blown by the air conditioner motor becomes cold after passing through the evaporator.
The car AC sometimes blows cold and sometimes hot, which I think is quite a common issue. In repair practice, I often encounter this problem with various causes. For example, insufficient or leaking refrigerant can cause unstable compressor pressure, leading to intermittent operation; or a faulty temperature sensor misjudges the cabin temperature, causing the system to adjust incorrectly. A clogged expansion valve can also result in intermittent cooling. A malfunctioning fan motor may cause poor airflow and uneven cooling. Additionally, electrical issues like poor relay contact or loose fuses can make the AC unstable. I recommend not delaying and taking the car to a professional repair shop for inspection to avoid accidents while driving. Regular AC maintenance is key—cleaning the condenser and checking the filter every six months can greatly reduce such annoyances. Safety first—a malfunctioning AC not only affects comfort but may also cause driving fatigue.
As an ordinary person who has driven for a long time, I have personally experienced such erratic behavior from the air conditioning. That time while driving to work, the AC suddenly blew cold air, then switched to hot air, which was really frightening. Possible reasons include incorrect temperature mode settings, the system automatically switching between internal and external circulation, or faulty sensors misreading data. Additionally, a dirty filter blocking the air ducts or a fan speed fluctuating can cause temperature instability. Aging circuits, such as worn switch contacts, might also be the culprit. That time, I quickly pulled over to check the manual, and later had the compressor repaired at a shop to fix the issue. It's advisable to usually use the automatic mode to stabilize the temperature and regularly clean the AC filter, at least once every quarter. If neglected, AC problems can affect the whole family's travel, especially making children and the elderly uncomfortable, which is even more dangerous. Addressing issues early saves money and hassle.
