Corolla AC and Temperature Sensor Issue

I had a similar issue with my Corolla. Same symptoms – error message and no A/C. It could well be the heat exchanger. The heat exchanger is part of the HVAC system. It allows heat to be transferred from a hot fluid to a cold fluid, without the two fluids mixing. In this case, to cool down the air that flows into the passenger cabin. Have you checked for any coolant leak around the area?

Thanks for the quick reply! Coolant leak is the next thing I will check. If it ends up being the heat exchanger's temperature sensor as suspected, should I replace just the sensor or the entire heat exchanger assembly? Is there a way to test the sensor itself, perhaps with a multimeter?

While you could test the sensor, in my experience, if the sensor is faulty, the entire heat exchanger assembly is often recommended. It’s a bit more expensive upfront, but it ensures that all the components are working correctly together and prevents further issues down the line. And regarding the coolant leak: any loss of coolant can cause air to enter the cooling system, which can prevent the HVAC system from operating correctly. So if you see one, you need to get it sorted either way. I would visit a workshop.

Took it to the shop, and you were spot on! Turns out the temperature sensor in the heat exchanger was indeed defective, which in turn led to the air conditioning control unit malfunctioning. Replacing the heat exchanger cost me around 980€. Appreciate your insight!