Why is the rear air conditioning in the BMW 3 Series not cooling effectively?
2 Answers
The reason why the rear air conditioning in the BMW 3 Series is not cooling effectively is that the power supply for the refrigerant pressure sensor and the potentiometer of the rear seat area fresh air grille in the JB (Junction Box) is controlled by the same power supply module. When the power supply of one sensor is short-circuited to ground, it affects the power supply of the other sensor. Here is more relevant information: 1. Turning on the air conditioning cooling in the BMW 3 Series: Press the button marked as 4 in the diagram to activate the cooling function. Once the cooling function is turned on, the air is cooled, dehumidified, and reheated according to the set temperature. After the engine starts, under certain climatic conditions, a layer of mist may briefly condense on the windshield. 2. Other issues: (1) When it is very hot in summer, an excessive amount of Freon refrigerant can cause the high pressure to exceed the limit, resulting in thunder-like vibrations from the engine and sometimes even boiling over. This is mainly due to the engine's relatively small power and the aging of some components. (2) If the air conditioning is turned on under these conditions, the engine may be overloaded and unable to drive the air conditioning compressor. Forcing the air conditioning to continue operating under such circumstances will accelerate vehicle wear and tear, and in severe cases, may even lead to vehicle self-ignition. Therefore, it is recommended to use appropriate automotive air conditioning additive products in such situations.
I've been driving a BMW 3 Series for several years, and the rear AC not being cool enough is a common issue. It's mostly due to improper climate zone settings—BMW has independent temperature controls for front and rear, possibly defaulting to prioritizing front control with less airflow to the rear. Another possibility is a dirty or clogged air filter, where dust buildup restricts airflow, making the rear more sensitive. Insufficient refrigerant is also a problem; if the whole car's cooling is weak, the rear effect worsens. Setting the temperature too high, improper vent direction, or external heat combined with more passengers in the rear dissipating heat faster can also make it seem less cool than the front. Try lowering the temperature, increasing fan speed, and cleaning the AC filter first. These minor adjustments can be done yourself. If it still doesn't improve, visit a professional shop, as pipe leaks or compressor issues also occur occasionally.
