Symptoms of a Bad or Failing Evaporator Temperature Sensor (Switch)

The evaporator temperature sensor or switch is a component commonly found on many road going vehicles. It is a part of the vehicle’s AC system, and as its name implies, detects and monitors the temperature of the AC system’s evaporator. The switch is usually installed directly on the AC evaporator or in close proximity, and monitors the temperature of the evaporator so that it can be properly regulated to stay within reasonable operating temperatures. When the sensor detects that the temperature is approaching high temperatures, the AC system will increase flow through the system to increase cooling and will reduce flow when it detects that the evaporator is cold to conserve power and prevent it from freezing over. When the switch fails or has any issues, it can hinder the performance of the AC system and even cause it to malfunction. Usually a bad or failing evaporator temperature switch will produce a few symptoms that can alert the driver of a potential issue that should be serviced.

1. No cold air from the AC system

One of the first symptoms of a potential problem with the evaporator temperature switch is no cold air from the AC system. If the evaporator temperature switch fails or has any issues that causes it to send an incorrect signal to the AC system, it can affect the system’s ability to produce cold air.

2. AC temperature fluctuates

Another symptom of a problem with the evaporator temperature sensor is fluctuating temperatures from the AC system. If the evaporator temperature sensor sends an incorrect or erratic signal to the computer, it can cause the AC temperature to behave erratically. The temperature may suddenly alternate between cold and warm, which will result in additional strain on the compressor, as well as consistently less cool cabin temperatures.

3. AC compressor does not activate

An AC compressor that does not activate is another symptom of a possible problem with the evaporator temperature sensor. The AC switch plays a direct role in activating and regulating the operation of the compressor, and when it fails, can sometimes even disable the compressor completely.

The evaporator temperature sensor plays a simple, but important role for the proper operation of the AC system. When the switch fails or has an issue, it can cause problems with the functionality of the entire AC system. If you suspect that your evaporator temperature switch may be having an issue, have the vehicle diagnosed by a professional technician, such as one from YourMechanic, to determine if your vehicle needs an evaporator temperature sensor replacement.


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Ben

41 years of experience
1410 reviews
Ben
41 years of experience
Volkswagen Beetle L5-2.5L - Heating AC - Houston, Texas
i am well satisfied with Mr Smith working on my car(s). He replaced the Jaguar fuel pump like an expert, and then he diagnosed the VW bug ac compressor and fixed it on the spot. I would recommend him to anyone with a car issue
Nissan Altima - Heating AC - Houston, Texas
Incredibly nice and took the time to show me the problem, including comparison pictures between my unit and what a new unit should look like.

Peter

43 years of experience
1321 reviews
Peter
43 years of experience
Saab 9-3 L4-2.0L Turbo - Heating AC - Phoenix, Arizona
He knows what he's doing. Very polite and explained everything. I would no doubt use him again. I highly recommend him.
Mazda Miata - Heating AC - Peoria, Arizona
We are so thrilled to have found Peter as our new mechanic. He is very thorough and knowledgeable. He is also friendly, professional, and extremely honest. He explained to us exactly what services were needed on our vehicle to repair the air conditioner and provided us with an written estimate of the cost. He literally saved us thousands of dollars in repair costs. A local major competitor quoted us a repair cost of a minimum of $1,400 and said that the cost would go up to $2,400 if they discovered an additional part was required. Peter charged us only $202, plus performed the work at our home. The air conditioner in our 2004 Mazda Miata has honestly never worked so great--it always blew out warm air. We just assumed it was how that particular car was manufactured. We would highly recommend Peter to anyone who is in need of an experienced and honest mechanic.

Pedro

31 years of experience
78 reviews
Pedro
31 years of experience
Chrysler PT Cruiser L4-2.4L - Heating AC - Portage, Indiana
Pedro was wonderful! He was early first and foremost. He was very professional and he explained things to me. He worked quickly and was very thorough. Very happy with his service.

Manuel

32 years of experience
580 reviews
Manuel
32 years of experience
Ford Taurus V6-3.0L - Heating AC - Long Beach, California
Good guy. Knows his stuff. Knowledgeable and straightforward with diagnostics and repair costs. I’d love to work with him again! Thank you Manuel!

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