MrNoodly said:
With the windows and doors closed, most outside air comes in through the HVAC ducts, even when the fan is off. So switch it to Max AC. That closes the intake. And when you start the van on freezing morning, keep it on Max AC so it recirculates interior air instead of sucking in outside air. Just turn the temperature way up.
What he said^^^!
Also some vehicles have a separate button for recirc, so you can set to heat and recirc instead of max AC.
It will have a logo something like this...
As for drafts elsewhere, use a dollar bill and a thin shopping or dry cleaning bag...
You close your doors with the dollar bill laying across the seal and tug it gently. If it is slipping out easily, you have a "dead spot" in your seal.
You might need to open/close the doors a few times and check at different spots.
Take the walmart bag and cut out one rectangular panel from one side of the bag, about the size of a sheet of copier paper.
Next cut strips length wise about 1/2" wide in the bag, leaving one end uncut.
You are creating a curtain of long thin streamers.
Tape the uncut end along a wire coat hanger so the streamers hang down.
With your vehicle closed and all vents closed and any fans or HVAC off, hang the streamer curtain in front of vents, fans, doors, etc and hold still to let air settle.
Look for any movement or blowing.
I did this around my house to find air leaks and to aim the adjustable vents on my wall mount Mitsubishi AC/Heat units to eliminate deadspots.
For fixing door issues, check Amazon for "D" shaped self-adhesive rubber weather stripping.
More durable, less absorbent than the foam stuff.
The problem with caulk is it's not meant to be an "active" seal, in areas that open/close.
It is meant for sealing fixed gaps.
You might be able to lay down a bead, let it cure and use it like weatherstripping, but other products will do a better job.
