In my 98 ram when I put the havac panel to heat and have the fan off I am getting smoke coming out of the vents slowly, it looks kida like a lit cigarette, and when I turn it to cold it goes away! Also I recently changed my t-stat and the truck warms up good but produces very little heat if any, anybody know what this is so I can fix it and have heat in my truck when im driving in 11 degree weather in the morning!