What are the symptoms of a faulty evaporator temperature sensor?
3 Answers
The function of the evaporator temperature sensor is to detect the temperature of the evaporator and regulate the operating time of the air conditioning system. When the evaporator temperature sensor is damaged or fails, the temperature of the refrigeration system cannot be properly controlled. When the temperature reaches the set requirement, it disconnects the compressor circuit, causing the compressor to stop working. When the temperature rises above a certain value, it reconnects the compressor circuit. More details are as follows: 1. Working principle of the evaporator temperature sensor: After turning on the air conditioning, the evaporator continuously cools. When the temperature reaches the set value, it sends a signal to stop the compressor. If it continuously sends signals to the compressor, the compressor will keep working. When the temperature meets the set requirement, it disconnects the compressor circuit, stopping the compressor. When the temperature exceeds a certain value, it reconnects the compressor circuit. 2. Function: The evaporator temperature sensor serves to protect the air conditioning system by preventing frost formation on the evaporator surface, which would reduce heat exchange efficiency. Generally, a surface temperature of 2-4°C on the evaporator is considered the frost formation temperature, and this feedback is sent to the AC switch to control its on/off state. The high and low pressure switch signals are fed back to the vehicle ECU to control the compressor's on/off state. Both mechanisms are designed to protect the automotive air conditioning system.
I remember last summer when I was driving to the beach, the air conditioning suddenly malfunctioned—cold air came and went intermittently, accompanied by the compressor buzzing nonstop, leaving me drenched in sweat. A faulty evaporator temperature sensor causes exactly these symptoms, primarily leading to uneven cooling—sometimes freezing cold, other times scorching hot—because the sensor fails to accurately monitor the temperature, throwing the AC system into chaos. The compressor may cycle on and off frequently, increasing noise and fuel consumption, and over time, it could even cause the evaporator to freeze up and block the air ducts, reducing airflow. What’s even more frustrating is that the defogging function might fail on rainy days, blurring visibility and increasing risks. I learned from my mechanic friend that if this part fails, it’s crucial to replace it promptly to avoid damaging the entire AC system and incurring higher costs. During routine maintenance, take care to prevent moisture from seeping into the sensor’s connector to reduce the likelihood of failure. In short, don’t delay—safety comes first.
From years of car maintenance experience, the most common symptom of a faulty evaporator temperature sensor is uncontrolled air conditioning cooling—either freezing cold or no cooling at all. The compressor, unable to regulate accurately, will cycle on and off repeatedly, causing harsh noises and increased fuel consumption. Airflow temperature fluctuates significantly, potentially switching from cold to warm or even hot air abruptly. In severe cases, the evaporator is prone to frosting and blockage, noticeably reducing airflow from the vents and impairing cabin air circulation. Some vehicles may also display an air conditioning fault warning on the dashboard. The fix isn't overly complicated: it's best to use diagnostic tools to read fault codes and confirm if the sensor is the issue—replacing it with a new one usually resolves the problem. To prevent this, avoid running the air conditioning at full load for extended periods during regular use. Never ignore the issue, as it can be dangerous during summer heat or when defogging is needed.
