What does REST on the air conditioner mean?

[MiaRose]

REST on the air conditioner refers to the residual heat function. This feature utilizes the engine's residual heat to continue providing warm air inside the vehicle for up to half an hour after the engine is turned off, after which it automatically shuts down. The REST button function is particularly suitable for short-term parking and engine shutdown in winter, as it helps maintain the interior temperature, preventing it from dropping rapidly. When restarting the vehicle, there is no need to turn on the air conditioning system to reheat the interior. To activate it, simply press the "REST" residual heat control button on the central console after turning off the engine. Do not immediately turn on the warm air when starting a cold engine. Since the engine has just started, the radiator temperature is very low in winter. Turning on the air conditioning will not quickly raise the car's temperature but will instead increase the engine's load and delay the normal rise in engine temperature. The engine should be warmed up first, and the heater should only be turned on after the engine temperature gauge reaches the midpoint. At the same time, set the air circulation to external circulation to allow the cold air inside the car to be expelled. After waiting for 2-3 minutes, the air circulation can then be set to internal circulation.

[OKathryn]

When I first bought my car, I was also curious about the REST button on the air conditioning. Later, I figured out that it utilizes the residual heat from the engine. After parking and turning off the engine, if you press the REST button, the air conditioning fan will blow warm air using the remaining heat from the engine, maintaining a comfortable temperature inside the car for about ten minutes. I often use it in winter when refueling or running to the supermarket to keep the interior cozy. It’s much more fuel-efficient than restarting the engine and also reduces emissions. However, note that the engine needs to be sufficiently warm for it to work effectively—performance is poor in summer or when the engine is cold. Occasionally, people mistake it for a malfunction, but it’s actually a clever design. In short, REST is a thoughtful and energy-saving little helper.

[MarleyFitz]

From a technical perspective, the REST function of the air conditioning system is a waste heat recovery mechanism. When you park and turn off the engine, the engine cools down slowly while remaining at a high temperature. The REST mode activates the fan system to channel that residual heat into the cabin. This allows the heating to be maintained without relying on electrical power. Based on my testing, it's only effective for short stops, with optimal performance within 5 to 15 minutes. Operation is straightforward: simply press the button before turning off the ignition. However, it's important to ensure the cabin temperature is set appropriately to avoid energy waste. This feature originated from designs for cold regions in Europe and North America, helping drivers maintain warmth during brief winter stops. It places minimal strain on the electrical system and can extend the lifespan of AC components.

[DelJaxon]

As an energy-saving enthusiast, I highly recommend the REST function in car air conditioning. Essentially, it utilizes residual engine heat to blow warm air after parking, so I don't need to restart the engine just for warmth. The savings on gasoline may seem small, but they add up significantly with each parking instance. For example, when refueling, I press the REST button, close the windows, and maintain a comfortable temperature for 5-10 minutes. This is more eco-friendly than running the engine for heating, reducing carbon emissions. The operation is also foolproof, easy even for beginners. However, remember to use it only when heating is needed, not during summer. Overall, it's a small trick that helps me cultivate energy-saving habits in daily driving.