* The engine is not producing as much heat. When you are driving, the engine is working harder and producing more heat. This heat is used to warm the cabin of the truck. However, when you are idling, the engine is not working as hard and producing less heat. This can cause the cabin of the truck to cool down.
* The air is moving faster over the truck. When you are driving, the air is moving faster over the truck. This can help to cool the truck down, especially if the outside air is cold.
* The heater core is not working properly. The heater core is a small radiator that is located in the dashboard of the truck. It is responsible for heating the air that comes out of the vents. If the heater core is not working properly, it can cause the cabin of the truck to cool down.
If you are experiencing this issue, you should take your truck to a qualified mechanic to have it diagnosed.
