What are the reasons for two out of four car air conditioning vents not cooling?

[JonathanFitz]

There are two main reasons why two out of four car air conditioning vents are not cooling: 1. Dual-zone climate control setting: Many current vehicle models, especially mid-to-high trim levels, are equipped with automatic air conditioning systems featuring dual-zone climate control. This divides the car's left and right sides into two independent temperature zones, allowing the driver and passenger to separately control each zone's temperature. If the temperature setting for one zone is too high, it can result in warm air blowing from half of the vents. The solution is to press the "DUAL" button on the air conditioning control panel to deactivate the dual-zone function, which will restore normal vent temperatures. 2. Low refrigerant level: The air conditioning system pressure needs to be checked using a refrigerant charging gauge.

[VonVincent]

A couple of years ago, my car had a similar issue where the left AC vent blew cold air while the right side blew hot air. This is most commonly caused by a stuck air blend door actuator - that small motor controlling air direction. When I disassembled the center console, I found the guide vane stuck in mid-position, blocking both vents with the damper. Of course, it could also be a broken flap shaft in the air distribution box, or poor contact in the mode motor. Another possibility is uneven refrigerant distribution due to overly long AC lines, especially noticeable in older vehicles with aging pipelines. I remember fixing it myself by replacing the actuator with a used part for just 80 yuan.

[VanDaniel]

As someone who frequently helps friends with car inspections, I've found that this kind of one-sided AC failure is 80% likely caused by issues with the dual-zone climate control system. Dual-zone AC systems rely on independent air mix doors to regulate temperature. If an actuator signal is interrupted or stuck, it can block the cooling pathway. Additionally, uneven evaporator frosting can lead to insufficient cooling on one side, especially in models with frequent compressor cycling. I recommend connecting a diagnostic tool to read fault codes, focusing on checking the servo motor resistance values and air door displacement data, rather than rushing to add refrigerant or replace the AC pump.

[KadenMarie]

I just asked the mechanic at the repair shop, and he said that for this kind of issue, the first thing to check is the vehicle configuration. For ordinary manual air conditioning, if the vents aren't cold, it might be due to a faulty blower resistor causing uneven airflow, or the air ducts for the driver and passenger sides coming loose. For higher-end models, it's mostly likely a malfunctioning zone temperature control sensor or a software glitch—resetting the air conditioning module can sometimes fix it. Remember to check if the air filter is too dirty and blocking specific vents; this is the least expensive fix and can be done yourself. The mechanic also reminded me not to overlook the situation where the surface of the air conditioning condenser is covered with willow catkins or insect remains, as this can indirectly lead to uneven cooling.