Here’s what that little bubble on top of your dashboard is for – Jalopnik

Have you ever noticed that little domed structure on top of your dashboard, sitting quietly in its own corner, unlike the many distracting doo dads of a modern car interior? Have you ever wondered what it was for? Maybe not, because you have much more important things to think about. Well, that’s why we’re here. We wonder about the stupid things so you don’t have to. And you might be surprised to learn that that strange little object on your dashboard has a function. It plays an important role in regulating the temperature in your vehicle.

That little object is called a solar load sensor and, as the name suggests, measures the amount of sunlight streaming into your car through the windows, along with the sun’s azimuth and altitude. Why does it do that? Anyone who has ever felt warm in a closed car with the windows closed on a cool day knows that ambient temperature is only part of the story when it comes to how warm or cool a car’s interior is. This small sensor allows your car’s climate control system to take sunlight into account when heating or cooling the vehicle.

What happens if your sensor doesn’t work? On hot days, your air conditioning may not work hard enough. Your heating may not work properly even on sunny winter days. Without the solar load sensor, your HVAC system cannot account for sunlight, and that is a big factor affecting your car’s temperature.

What does the climate control do with that signal? The HVAC system uses the strength of the signal to determine fan speed and how to mix the warm and cool airflow in the cabin. Your car’s climate control system includes mixed doors, which control whether warm or cool air is sent to the cabin. Depending on whether the cabin needs to be cooled or heated, the air through these doors is routed through the AC evaporator or the heater core.

The signal from the sun load sensor is used to control the direction in which these doors open. If it is a very sunny, hot day, the sun sensor sends out a weak signal and the mixing doors open wide to let in more cool air through the AC evaporator. On a cloudy day or at night the opposite happens. The signal from the solar load sensor will be stronger, resulting in less cool air being sent into the cabin. If you think that’s impressive, check out Nissan’s new paint that cools your car.

Is something on your dashboard covering one of the solar load sensors (often there are two)? This can disrupt the functioning of your AC, especially if sunlight is completely unable to reach the sensor. You may also want to try cleaning the visible part of the sensor, as enough dirt can block sunlight. Please note that a faulty sensor will cause an error code (usually a B code). The code will not necessarily activate a check engine light, but it will display on your OBD-II scanner. A less definitive way to test the sensor is to compare how your AC works with the sensor covered and uncovered. But do this while the car is parked outside on a sunny day, as the sensor is calibrated to sunlight and not to your garage’s interior lights. We must also take into account that the solar load sensor is not the same as the headlight sensor which looks the same but turns on your automatic headlights. So make sure you test correctly.

Now you know what that little dot on your dashboard is; just make sure you don’t cover it. And while you’re at it, check out our tips for keeping your air conditioner cold.