Heater on 2002 Nissan Quest

The heater and defrost work but no heat comes. The heat comes out only when driving. Why?

Asked by for the 2002 Nissan Quest
Most common reason that you will have heat when driving and not at idle is that there is an air pocket in the cooling system. This can be caused by a leak in the system. I would recommend that you have this checked out immediately. An air pocket in a cooling system can cause a large amount of damage if it's not caught early. Best of luck