Symptoms of a bad evaporator temperature sensor
A bad evaporator sensor typically causes your vehicle's air conditioner to stop working, freeze too much, or blow warm air. The evaporator temperature sensor tells your vehicle's brain (the computer) to either drop or increase the temperature to dodge a freeze-up; it acts like a thermometer to prevent things from getting too cold or hot inside, protecting wires, circuits, etc. The evaporator temperature sensor sits behind your dashboard, near the glove box.
A faulty evaporator temperature sensor can cause the air conditioning system to behave erratically. Since this sensor monitors the temperature of the evaporator to prevent freezing, a malfunctioning sensor might give incorrect readings, causing the A/C to cycle on and off too frequently or not blow cold air at all. This results in fluctuating cabin temperatures and an uncomfortable ride.
If the sensor incorrectly detects that the evaporator is too cold, it may send signals to shut off the A/C compressor prematurely, preventing the system from cooling properly. On the other hand, if the sensor fails to detect freezing temperatures, the compressor might stay on too long, which can lead to an overworked system, increased wear, and potential damage to other A/C components.
3. Ice Buildup on the Evaporator Coils
A defective evaporator temperature sensor might fail to detect when the evaporator is too cold, allowing moisture to freeze on the coils. Over time, this ice buildup can block airflow, reducing the effectiveness of the A/C and causing the system to struggle to cool the cabin. If ice forms, you may notice weaker airflow or even a complete loss of cold air until the ice melts.
If the sensor incorrectly tells the A/C system that the evaporator is already cold when it isn’t, the system may stop cooling even when you need it. This can result in warm air coming from the vents even though the A/C is turned on.
5. Increased Cabin Humidity
The evaporator helps remove moisture from the air before it enters the cabin. If the sensor malfunctions and prevents the A/C from functioning correctly, it can lead to higher humidity levels inside the vehicle, making the air feel damp and uncomfortable.
In some cases, a completely failed evaporator temperature sensor may prevent the A/C system from turning on at all. This happens because the climate control system relies on this sensor to regulate cooling operation, and without a proper reading, it may default to a fail-safe mode, shutting down the system entirely.
On some vehicles, a failing evaporator temperature sensor can trigger the Check Engine Light (CEL) or an A/C system warning light. If the vehicle’s onboard computer detects incorrect temperature readings or a failure in the sensor circuit, it may store a trouble code, which can be retrieved using a diagnostic scan tool.
