What is the square wave button next to the AC?

[StKylie]

The square wave button next to the AC is the defogging and heating function button. Here are the relevant introductions: Introduction 1: There are generally two defogging buttons in a car, one is the front windshield defogging button, usually marked with a fan shape and a wave line, and the other is the rear windshield defogging button, usually marked with a square and a wave line. Introduction 2: The front windshield defogging relies on the air conditioning system, with dedicated air vents located near the front windshield on the center console. The rear windshield defogging mainly uses electric heating wires. After turning on the rear windshield defogging switch, the heating wires will generate heat, thereby achieving the purpose of helping to defog.

[SanDaniela]

That button with a square and a wavy arrow is the air recirculation mode switch. I remember testing it specifically on the highway last week—when turned on, it stops drawing air from outside and instead circulates the air inside the cabin. This is especially useful when driving through tunnels or behind trucks with strong exhaust fumes, as it prevents odors from entering the cockpit. But be aware that prolonged use can cause the windows to fog up, particularly in winter when the heater is on, as moisture can’t escape. Nowadays, I use recirculation mode in traffic and switch to fresh air mode on the highway, balancing air freshness and fuel efficiency. The manual mentions that some models can sync this with automatic climate control, but my older car doesn’t have that advanced feature.

[LaNadia]

This is the recirculation button, which I usually refer to as the cabin air recirculation button. I press it every time I pass a garbage truck or on smoggy days, and I can clearly feel the reduction of dust inside the car. Last time when I took my child to the hospital, the pediatrician specifically mentioned that this mode is very helpful for people with allergies. However, once I forgot to turn it off during a two-hour long drive, and I felt dizzy when I got out of the car, probably due to the high carbon dioxide concentration. Now I treat it as a temporary protective switch, usually turning it on for about twenty minutes before switching back to auto mode, which is both comfortable and safe.

[McWyatt]

The square button with waves on the air conditioning panel controls the air source. When pressed, the fan only recirculates air from inside the cabin without drawing in external airflow. Using this mode in summer cools the car faster, but avoid it during winter defogging as it can cause window frosting. I remember a friend's new energy vehicle had an automatic mode for this function—it would switch automatically when detecting excessive PM2.5 levels. For conventional models, it's recommended to use this feature at dusty construction sites or during pollen season, but otherwise, it's best to keep the system in fresh air mode.

[StArthur]

That square wave button is the recirculation switch. When pressed, the cabin becomes a closed environment. The most noticeable effect is faster cooling when the AC is on, as it doesn't have to process hot outside air. But two things to note: 1) Turn it off immediately if the windshield fogs up, and 2) Prolonged use can lead to oxygen deprivation. I've tested different car models - Japanese cars typically exceed CO2 limits within 30 minutes, while German cars last longer. Now I've developed a habit: turn it on in heavy exhaust areas, then switch back on clear roads. It's more energy-efficient than automatic AC.

[MacXavier]

This is the air conditioning system's recirculation button, professionally known as re-circulation mode. It was originally designed for special road conditions: for example, it can block harmful gases when passing through chemical plant areas and prevent dust from entering during sandstorms. I have tested its three effects: saving 20% fuel when using the AC, reducing the load on the AC compressor, and improving cabin sealing at high speeds. However, the drawbacks are also obvious—oxygen levels drop after half an hour, making people drowsy, and the windows are prone to condensation. It is recommended to use it with automatic air conditioning or develop a habit of switching it off periodically.