this won't defrost the windshield but it sure warms up the seat faster. after cold start up use the AC MAX at high heat setting it recycles the air from inside the cab and not outside colder air. it works!! helps keep cab fresher too!! (fumes)

 

If you really want it to warm the cabin quick plug it in for a couple hours. If you leave the heat control set to defrost/hot when you shut it down it will also keep a big enough spot of frost open allowing you to drive right away.

 

just do what I do and never turn the dang thing off after all diesels were originally designed to run all dat every day for drilling purposes