BMW 640i xDrive Air Conditioning Evaporator Temperature Sensor Replacement Cost

The air conditioning refrigerant system is a large system designed to cool the evaporator core in order to cool the air in the cabin. This system works well, but needs to be monitored to ensure the refrigerant system is cooling the evaporator core sufficiently to cool the inside of the vehicle and ensure it does not get so cold it freezes. For this purpose, the air conditioning evaporator core temperature sensor is used to monitor the efficiency of the system.

Mounted on the evaporator core, this thermal sensor measures the temperature of the evaporator core constantly, and communicates the temperature back to the air conditioner control module. The control module will determine if the evaporator core is too cool, too warm, or just right. If too warm, the control module can adjust compressor output or expansion valve flow rates, which normally moves the evaporator core into the appropriate range. If the evaporator core does not move to an acceptable temperature range, the temperature sensor will likely stop function of the air conditioning system.

Like all air conditioning refrigerant system issues, an improperly functioning or failed evaporator temperature sensor will lead to decreased performance of the air conditioning system for the vehicle. Incorrect readings from the temperature sensor may cause the air conditioner to become extremely cold or warm. In either case, the air conditioner will likely stop functioning, and the a/c button in the cabin may begin blinking. The air conditioner may blow cold air intermittently, but will always return to a non-functional state.